CG è sostenuto da sovvenzioni dal Agence National de la Recherche (ANR-13-JSV1-0008), a titolo del Settimo programma quadro dell&#39;Unione europea (Marie Curie integrazione carriera n˚8304162) e dal Consiglio europeo della ricerca (CER) nell&#39;ambito di Orizzonte dell&#39;Unione europea 2020 programma di ricerca e innovazione (ERC Starting Grant n˚639300).

1. Ligand coniugazione di biglie magnetiche Nota: coniugazione Ligand viene eseguita utilizzando superparamagnetiche perline tosyl-attivato con un 2,8 micron di diametro (concentrazione della soluzione 10 8 perline / mL, 30 mg perline / ml). Il seguente protocollo si basa su campioni di circa 2 x 10 5 cellule, che corrispondono alle MRC-5 cellule cresciute al 80% di confluenza in una piastra di coltura tissutale 60mm. Regolare il volume di perline e reagenti di conseguenza se si utilizza lastre di dimensioni diverse o cellule in diverse confluenze. Utilizzare una quantità di perline superparamagnetici per avere 2 perle per cella. Pertanto, 4 x 10 5 perline sono necessari per una piastra 60 mm. <ol><li> Accuratamente risospendere le sfere nel flacone originale vortex almeno 30 s. Aliquota 40 ml di perline superparamagnetiche risospesa (corrispondenti a 4 x 10 6 sfere) in 1,5 ml provetta. </li><li> Posizionare il tubo su una Separati magneticasul basamento per separare le perline magnetiche dalla soluzione. Eliminare il surnatante, rimuovere il tubo dal supporto separazione magnetica e risospendere le sfere in 1 ml di 0,1 M Na-fosfato pH 7.4. <ol><li> Ripetere la fase di lavaggio due volte con 1 ml di 0,1 M Na-fosfato pH 7.4. </li></ol></li><li> Dopo l&#39;ultimo lavaggio, risospendere le sfere in 1 ml di 0,1 M Na-fosfato pH 7.4. </li><li> Unire 100 mcg bovina fibronectina (FN) o qualsiasi altro recettore adesione delle cellule ligando al 1 ml 0,1 M Na-fosfato pH 7.4 contenente microsfere e mescolare pipettando. </li><li> Ripetere passaggi precedenti sostituendo FN o qualsiasi altro legante specifico con BSA, poli-D-lisina o apo-transferrina per i controlli negativi. </li><li> Facoltativamente, per l&#39;analisi del gel, prendere una aliquota di 10 ml di soluzione ligando per l&#39;analisi di efficienza reticolazione e mescolare con un volume adeguato di concentrato Laemmli Sample Buffer. </li><li> Incubare perline con la soluzione contenente ligando per 12-24 ore a 37 ° C in un rotore. </li><li> Se aggregati tallone compaiono dopo la reazione si è verificato, ultrasuoni (continua Potenza 39 W) per non più di 10-20 s. </li><li> Isolare le perline con supporto separazione magnetica, aspirare la soluzione rimanente e aggiungere 1 ml di PBS / 0,2% di BSA pH 7,6 soluzione. Incubare per 1 ora a rotore a 37 ° C. </li><li> Lavare perline usando un magnete due volte con 1 ml di PBS / 0.2% BSA pH 7,6. perline risospendere in 1 ml di PBS / 0.2% BSA pH 7,6. </li><li> perline Sonicare se aggregati appaiono per non più di 20-30 s. </li><li> Facoltativamente, rimuovere una aliquota di 10 microlitri di analizzare l&#39;efficienza di accoppiamento da Western Blot (mescolare con un volume adeguato di concentrato soluzione tampone Laemmli). </li><li> Procedere alla cella saggi o perline Conservare a 4 ° C per un massimo di 1 mese. </li><li> Facoltativamente, eseguire un gel SDS-PAGE e macchia con Coomassie blu per analizzare FN reticolazione alle sfere magnetiche. </li></ol> 2 applicazione di forze tensionali sulle Beads Ligand rivestite Bound di Adesione recettori presenti sulla dorsaleSuperficie delle cellule <ol><li> Culture cellule aderenti in 60 millimetri piatto di coltura tissutale nel terreno di coltura appropriato (di solito DMEM 4,5 g / L D-glucosio integrato con FCS 10%) fino a raggiungere l&#39;80% di confluenza. </li><li> Preparare tampone di lisi non denaturante non ionico (20 mM Tris HCl pH 7,6, 150 mM NaCl, 2 mM MgCl 2, 0,1% NP-40) Tubi e rilassarsi microcentrifuga. </li><li> Pellet le perline ligando rivestite da sezione 1.10 e risospendere in 1 ml di PBS / 0.2% BSA pH 7,6. Aggiungere 100 ml della soluzione di perline ligando rivestite di 5 ml di terreno di coltura caldo e vortice. </li><li> Aspirare media in 60 millimetri piatto cultura e aggiungere 5 ml di mezzo di crescita caldo integrato con perline. </li><li> Incubare per 20 minuti in condizioni di coltura cellulare (37 ° C e 5% CO 2) per consentire alle sfere di sedimenti e aderire alle cellule. E &#39;fondamentale non superare 20 minuti da perline possono essere internalizzati dalla fagocitosi. </li><li> Opzionalmente, osservare le perline sotto un microscopio ottico con un 10X o 20X objective e verificare l&#39;adesione tallone leggermente agitando il piatto di discriminare tra perline attaccate e galleggianti. </li><li> Mantenendo il piatto cultura nell&#39;incubatrice, scambiare la normale coperchio piatto per un coperchio con un tondo 38 millimetri magnete al neodimio attaccato sulla faccia superiore. Il magnete è tenuto in posizione da due piccoli magneti al neodimio 13 mm posizionato sulla faccia inferiore del coperchio. Poiché i magneti sono molto potenti, manipolarle con attenzione. </li><li> Incubare le cellule sottoposte a tensione per i punti di tempo desiderati in condizioni di coltura cellulare (37 ° C e 5% CO 2). </li><li> Dopo il trattamento, posizionare piatto su ghiaccio e accuratamente aspirare l&#39;intero supporto dal piatto. </li><li> Aggiungere 300 ml di tampone di lisi cellulare, e incubare per 10 min in ghiaccio. Raccogliere il lisato utilizzando un raschietto cellulare e trasferirli in un pre-raffreddata 1,5 ml provetta. </li><li> Pellet le perline magnetiche utilizzando il supporto separazione magnetica e trasferire il lisato cellulare totale in un pre-raffreddamentocato 1,5 ml provetta. Conservare questa frazione a -20 ° C per ulteriori analisi. </li><li> Lavare le perline 3 volte con 1 ml di tampone di lisi ghiacciata. Aggiungere 50 microlitri di tampone campione Laemmli al pellet tallone, mescolare pipettando e far bollire a 95 ° C per 5 minuti utilizzando un riscaldatore a secco. Questa frazione contiene gli isolati complessi di adesione. Procedere alla analisi biochimiche o conservare a -20 ° C. </li><li> Dal lisato cellulare totale ottenuto dopo la separazione perline (circa 300 ml), rimuovere una aliquota di 50 microlitri per l&#39;analisi Western Blot. NOTA: Le 250 microlitri di sinistra può essere utilizzato per ulteriori studi biochimici, quali studi di interazione proteina-proteina (immunoprecipitazione, saggi GST pull-down) o esperimenti di attività GTPasi (cambiando il tampone di lisi può essere necessario a seconda del GTPase di interesse). </li></ol>

<ol>
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Gli autori dichiarano interessi finanziari concorrenti.

Il metodo descritto qui costituisce un approccio semplice da applicare tensione ai recettori di adesione cellulare, e consentire loro purificazione successiva. Tuttavia, alcuni passi sono fondamentali per eseguire efficiente purificazione adesione e potenziale di ottimizzazione può essere fatto a seconda delle recettori di adesione mirati. Vi presentiamo i potenziali problemi che si possono riscontrare in basso. Abbiamo usato sfere magnetiche 2,8 micron di diametro, ma perle più grandi pos...

In metazoi, tensione meccanica dirige lo sviluppo dei tessuti e l&#39;omeostasi attraverso la regolazione di una miriade di processi cellulari quali la proliferazione, il differenziamento e la sopravvivenza 1, 2. tensione meccanica può derivare dalla matrice extracellulare o può essere generato da cellule aderenti, quale campione loro ambiente extracellulare attraverso l&#39;apparato contrattile actomyosin che tira sulla matrice extracellulare e sonde sua rigidità attraverso molecole sensibili alla tensione. In risposta alla tensione, proteine ​​di adesione meccanosensibili subiscono cambiamenti conformazionali che si innescano cascate di segnalazione complessi. A loro volta, queste vie di segnalazione orchestrano un mechanoresponse comprende proliferazione, differenziazione e sopravvivenza che regola il comportamento cellulare per l&#39;ambiente extracellulare. Tali processi possono essere risolte in un periodo di tempo breve termine (secondi o minuti) per alimentare rapidamente indietro sul ciclo di mecha<html> notransduction modificando le strutture meccanosensibili. Per esempio, aderenze integrine basato rafforzano in risposta alla tensione attraverso Rho GTPasi mediata citoscheletro rimodellamento 3, 4, 5. In parallelo, altre vie di segnalazione sono attivati nel giro di ore e giorni per controllare programmi genetici che alla fine influenzano il destino della cellula 6. Considerando che, molti studi hanno messo in evidenza l&#39;effetto della matrice di rigidezza sul determinismo cellulare e lo sviluppo della malattia 1 2, i precisi meccanismi molecolari della meccanotrasduzione adesione mediata rimangono ancora sfuggente. Diversi approcci sono stati sviluppati per studiare gli effetti delle forze di cellule generate o forze esterne sul comportamento delle cellule, compresi i sistemi di flusso, di trasferimento di fluorescenza di energia di risonanza (FRET) sensori -tensione 7,lass = &quot;xref&quot;&gt; 8, substrati compliant 9, pinzette magnetico, pinzette ottiche 10 e a forza atomica microscopia (AFM) 11. Qui vi presentiamo un protocollo utilizzando perline superparamagnetici per caratterizzare le vie meccanotrasduzione in risposta alle forze tensionali applicati ai recettori di adesione specifici. perline superparamagnetiche sono particelle che magnetizzare reversibilmente quando posto in un campo magnetico. Dopo rivestita con un ligando per un recettore specifico, queste perle forniscono un potente strumento per studiare gli effetti di applicazione della forza extracellulare. Questo metodo è stato convalidato da diversi studi 3, 5, 12 - 17 e presenta il vantaggio di facilitare ampiamente analisi biochimiche su cellule aderenti. Utilizzando sfere magnetiche rivestite di collagene simili seguiti da analisi biochimica, primi lavori ha registrato un aumentoproteina tirosina fosforilazione e dell&#39;attivazione RhoA in risposta alla tensione 5, 18, 19. Il metodo descritto qui di seguito è stato utilizzato anche con fibronectina (FN) perline Rivestiti di caratterizzare le vie di segnalazione a valle dalla tensione applicata al integrine 3. In questo studio, Guilluy et al. ha dimostrato che la tensione attiva RhoA attraverso il reclutamento dei due fattori di scambio guanina nucleotide (GEFs), larg e GEF-H1, a complessi di adesione integrine. Dato che, altri studi hanno dimostrato che GEF-H1 è reclutato a complessi di adesione in risposta alla tensione cellule generate utilizzando metodi differenti 20, 21, dimostrando la robustezza della metodologia descritta QUI. Come risultato, attivato RhoA stato mostrato per promuovere l&#39;adesione rinforzo, attraverso il rimodellamento del citoscheletro. Questo sistema è stato utilizzato anche per esplorare tensione applicata to recettori di adesione cellulare / cellula. Applicazione di forze su biglie magnetiche rivestite con il dominio extracellulare di E-caderina induceva un aumento delle assunzioni vinculin analogamente a integrine associato complessi di adesione 12. Collins e colleghi hanno osservato che l&#39;applicazione della tensione di PECAM-1 promuove integrina e l&#39;attivazione RhoA 13. Un altro approccio sperimentale utilizzando biglie magnetiche è lo studio della tensione applicata nuclei isolati. Utilizzando perle rivestite con anticorpi contro le proteine dell&#39;involucro nucleare nesprin-1, complessi dell&#39;involucro nucleare sono stati purificati per dimostrare che essi sono regolati in modo dinamico in risposta alle tensioni meccaniche 22. Questi risultati supportano la potenza del metodo nello studio dei percorsi meccanotrasduzione. Inoltre, mentre i sistemi di flusso o forza di trazione stimolare processi cellulari generale, sfere magnetiche si rivolgono specificamente un recettore di adesione cellulare utilizzando uno ligandi del recettore 13, 15. Un altro vantaggio di questo metodo è l&#39;isolamento di complessi di adesione mediante una procedura di purificazione di affinità ligando semplice. È ben noto che l&#39;aggiunta di perline ligando intonacato cellule lega recettori di adesione e induce il reclutamento di diverse proteine di adesione 23. Ulteriore applicazione di forze di sfere magnetiche rivestite ligando trasforma questi complessi di adesione in piattaforme macromolecolari che media diverse vie di segnalazione di tensione dipendente dal 4, 24. lisi cellulare seguita da concentrazione tallone utilizzando un magnete consente l&#39;isolamento delle piattaforme di adesione. Altri metodi utilizzati per purificare complessi di adesione sono già stati utilizzati in cellule aderenti. Essi combinano reticolazione chimica per conservare interazioni proteina-proteinaed una fase di lisi cellulare mediante detergente e flusso di taglio o sonicazione 20, 21, 25, 26, 27, 28. Il passo finale è la raccolta delle membrane plasmatiche ventrali risultanti contenenti i complessi di adesione. A differenza di questi metodi, perline magnetiche consentono un maggiore livello di purificazione di complessi di adesione cellulare orientando selettivamente una specifica famiglia di recettori di adesione. Perline magnetiche sono già stati utilizzati per depurare complessi di adesione in cellule non aderenti collegati a microsfere ligando rivestite 29, 30. Il metodo descritto qui di seguito imita situazioni biologiche in cui si applica una forza per un breve periodo prolungato (secondi ad alcuni minuti). Esso fornisce pertanto un potente strumento per studiare sia la composizione molecolare di complessi di adesione purificati ele vie a valle meccanosensibili di segnalazione. Qui vi presentiamo un protocollo sperimentale dettagliata per l&#39;utilizzo di sfere magnetiche per applicare forze tensionali di proteine ​​di superficie l&#39;adesione. Un magnete al neodimio permanente è posto sulla parte superiore della superficie coltura piatto. La faccia polare del magnete è posto ad un&#39;altezza di 6 mm in modo che la forza una singola 2,8 micron branello magnetico è costante (circa 30-40 pN) 31. La durata della stimolazione tensione viene determinato dall&#39;operatore a seconda della molecola di interesse e la sua scala di attivazione. Le cellule sono poi lisate, complessi di adesione sono purificati dalla separazione perline usando un magnete e analisi biochimiche vengono elaborate. Questo protocollo comprende la preparazione di perle superparamagnetici ligando-rivestito, e applicazione di tensione attraverso magnete seguita da analisi biochimiche. Inoltre, forniamo un campione rappresentativo di dati che dimostrino che la tensione applicata al adh integrina-basedesions induce adesione rimodellamento e altera la proteina fosforilazione della tirosina.

<table><tbody><tr><td>Neodymium magnets (on the upper face of 60 mm dish)</td><td>K&amp;amp;J Magnetics, Inc</td><td>DX88-N52</td><td>grade N52 dimension: 1 1/2&quot; dia. x 1/2&quot; thick</td></tr><tr><td>Neodymium magnets (on the lower face of 60 mm dish)</td><td>K&amp;amp;J Magnetics, Inc</td><td>D84PC-BLK</td><td>grade N42 dimension: 1/2&quot; dia. x 1/4&quot; thick Black Plastic Coated&amp;nbsp;</td></tr><tr><td>Dynabeads M280 Tosylactivated</td><td>Thermofisher</td><td>14203</td><td>superparamagnetic beads&amp;nbsp;</td></tr><tr><td>DynaMag-2 Magnet</td><td>Thermofisher</td><td>12321D</td><td></td></tr><tr><td>Fibronectin&amp;nbsp;</td><td>Sigma-Aldrich</td><td>F1141-5MG</td><td>Fibronectin from bovine plasma</td></tr><tr><td>Poly-D-Lysine</td><td>Sigma-Aldrich</td><td>P7280-5MG</td><td></td></tr><tr><td>Apo-Transferrin</td><td>Sigma-Aldrich</td><td>T1428-50MG</td><td>Bovine Apo-Transferrin</td></tr><tr><td>Bovine serum albumin</td><td>Sigma-Aldrich</td><td>A7906-500G</td><td></td></tr><tr><td>DMEM high glucose, GlutaMAX supplement, pyruvate&amp;nbsp;</td><td>Life Technologies</td><td>31966-021</td><td>DMEM+GlutaMAX-I 500 ml&amp;nbsp;</td></tr><tr><td>60*15 mm culture dish</td><td>Falcon</td><td>353004</td><td></td></tr></tbody></table>

analyzing cell surface adhesion remodeling in response to mechanical tension using magnetic beads

Meccanosensibili complessi di adesione cellulare, consentono alle cellule di percepire le proprietà meccaniche del loro ambiente. Recenti studi hanno identificato due molecole di forza-sensing in siti di adesione, e fattori di trascrizione della forza-dipendente che regolano l&#39;espressione genica specifica per lignaggio e guidano uscite fenotipici. Tuttavia, le reti di segnalazione di conversione della tensione meccanica in percorsi biochimici sono rimasti sfuggente. Per esplorare le vie di segnalazione impegnate su tensione meccanica applicata al recettore sulla superficie cellulare, microsfere superparamagnetiche possono essere utilizzati. Qui vi presentiamo un protocollo per l&#39;utilizzo di sfere magnetiche per applicare forze di proteine ​​di adesione della superficie cellulare. Usando questo approccio, è possibile indagare non solo forza-dipendente percorsi citoplasmatica segnalazione di vari approcci biochimici, ma anche l&#39;adesione rimodellamento isolamento magnetico di complessi di adesione attaccate alle perline rivestite ligando. Questo protocollo include la preparazione di ligando-coATED perline superparamagnetiche, e l&#39;applicazione di definiscono forze di trazione seguita da analisi biochimiche. Inoltre, forniamo un campione rappresentativo di dati che dimostrino che la tensione applicata ad adesione integrina-based innesca adesione rimodellamento e altera la proteina fosforilazione della tirosina.

Lo schema della tecnica è illustrata in Figura 1a. Dopo coniugazione ligando, sfere magnetiche vengono incubate con le cellule per 20 minuti, e quindi un magnete permanente è utilizzato per applicare forze di trazione di circa 30-40 pN per vario tempo. La figura 1b mostra 2,8 micron sfere magnetiche FN-rivestiti legati ai recettori di adesione cellulare MRC5. Le fasi di lavaggio di perline superparamagnetiche dopo la lisi cellulare sono cruciali e determin...

Watch this Scientific Journal Video about Analyzing Cell Surface Adhesion Remodeling in Response to Mechanical Tension Using Magnetic Beads at JoVE.com

Analyzing Cell Surface Adhesion Remodeling in Response to Mechanical Tension Using Magnetic Beads

aderenze superficie cellulare sono centrali in meccanotrasduzione, in quanto trasmettono tensione meccanica e avviare le vie di segnalazione coinvolte nella omeostasi dei tessuti e lo sviluppo. Qui, vi presentiamo un protocollo per sezionare i percorsi biochimici che si attivano in risposta a tensione, utilizzando microsfere magnetiche rivestite ligando e di applicazione della forza di recettori di adesione.

Analizzando cellulare superficie di adesione ritocca in risposta alla tensione meccanica utilizzando biglie magnetiche

Mechanosensitive cell surface adhesion complexes allow cells to sense the mechanical properties of their surroundings. Recent studies have identified both ...

analyzing-cell-surface-adhesion-remodeling-response-to-mechanical

Universidad de Cartagena UDEC

Research

JoVE Journal

Biology

8.4K Views.  Centre de recherche UGA - INSERM U1209 - CNRS UMR.  aderenze superficie cellulare sono centrali in meccanotrasduzione, in quanto trasmettono tensione meccanica e avviare le vie di segnalazione coinvolte nella omeostasi dei tessuti e lo sviluppo. Qui, vi presentiamo un protocollo per sezionare i percorsi biochimici che si attivano in risposta a tensione, utilizzando microsfere magnetiche rivestite ligando e di applicazione della forza di recettori di adesione. 

Video: Analyzing Cell Surface Adhesion Remodeling in Response to Mechanical Tension Using Magnetic Beads

Multiplexed Single-molecule Force Proteolysis Measurements Using Magnetic Tweezers

The generation and detection of mechanical forces is a ubiquitous aspect of cell physiology, with direct relevance to cancer metastasis1, atherogenesis2 and wound healing3. In each of these examples, cells both exert force on their surroundings and simultaneously enzymatically remodel the extracellular matrix (ECM). The effect of forces on ECM has thus become an area of considerable interest due to its likely biological and medical importance4-7.
	Single molecule techniques such as optical trapping8, atomic force microscopy9, and magnetic tweezers10,11 allow researchers to probe the function of enzymes at a molecular level by exerting forces on individual proteins. Of these techniques, magnetic tweezers (MT) are notable for their low cost and high throughput. MT exert forces in the range of ~1-100 pN and can provide millisecond temporal resolution, qualities that are well matched to the study of enzyme mechanism at the single-molecule level12. Here we report a highly parallelizable MT assay to study the effect of force on the proteolysis of single protein molecules. We present the specific example of the proteolysis of a trimeric collagen peptide by matrix metalloproteinase 1 (MMP-1); however, this assay can be easily adapted to study other substrates and proteases.

In this article we describe the use of magnetic tweezers to study the effect of force on enzymatic proteolysis at the single molecule level in a highly parallelizable manner.

Multiplex singola molecola Forza Misure proteolisi con delle pinzette magnetiche

The  generation and detection of mechanical forces is a ubiquitous aspect of cell physiology,  with direct relevance to cancer metastasis1, atherogenesis2 ...

Ricerca

Bioingegneria

Magnetic Tweezers for the Measurement of Twist and Torque

Single-molecule techniques make it possible to investigate the behavior of individual biological molecules in solution in real time. These techniques include so-called force spectroscopy approaches such as atomic force microscopy, optical tweezers, flow stretching, and magnetic tweezers. Amongst these approaches, magnetic tweezers have distinguished themselves by their ability to apply torque while maintaining a constant stretching force. Here, it is illustrated how such a &#8220;conventional&#8221; magnetic tweezers experimental configuration can, through a straightforward modification of its field configuration to minimize the magnitude of the transverse field, be adapted to measure the degree of twist in a biological molecule. The resulting configuration is termed the freely-orbiting magnetic tweezers. Additionally, it is shown how further modification of the field configuration can yield a transverse field with a magnitude intermediate between that of the &#8220;conventional&#8221; magnetic tweezers and the freely-orbiting magnetic tweezers, which makes it possible to directly measure the torque stored in a biological molecule. This configuration is termed the magnetic torque tweezers. The accompanying video explains in detail how the conversion of conventional magnetic tweezers into freely-orbiting magnetic tweezers and magnetic torque tweezers can be accomplished, and demonstrates the use of these techniques. These adaptations maintain all the strengths of conventional magnetic tweezers while greatly expanding the versatility of this powerful instrument.

Magnetic tweezers, a powerful single-molecule manipulation technique, can be adapted for the direct measurements of the twist (using a configuration called freely-orbiting magnetic tweezers) and torque (using a configuration termed magnetic torque tweezers) in biological macromolecules. Guidelines for performing such measurements are given, including applications to the study of DNA and associated nucleo-protein filaments.

Pinzetta magnetici per la misurazione di Twist and Torque

Single-molecule techniques make it possible to investigate the behavior of individual biological molecules in solution in real time. These techniques ...

Bead Aggregation Assays for the Characterization of Putative Cell Adhesion Molecules

Cell-cell adhesion is fundamental to multicellular life and is mediated by a diverse array of cell surface proteins. However, the adhesive interactions for many of these proteins are poorly understood. Here we present a simple, rapid method for characterizing the adhesive properties of putative homophilic cell adhesion molecules. Cultured HEK293 cells are transfected with DNA plasmid encoding a secreted, epitope-tagged ectodomain of a cell surface protein. Using functionalized beads specific for the epitope tag, the soluble, secreted fusion protein is captured from the culture medium. The coated beads can then be used directly in bead aggregation assays or in fluorescent bead sorting assays to test for homophilic adhesion. If desired, mutagenesis can then be used to elucidate the specific amino acids or domains required for adhesion. This assay requires only small amounts of expressed protein, does not require the production of stable cell lines, and can be accomplished in 4 days.

Here we present a simple, rapid method for characterizing the intrinsic adhesive properties of putative cell adhesion molecules. The secreted, epitope-tagged ectodomain of a cell adhesion molecule is captured from the culture medium on small, uniform functionalized beads. These beads can then be used immediately in simple bead aggregation assays.

Perlina di aggregazione saggi per la caratterizzazione di molecole di adesione cellulare putativo

Cell-cell adhesion is fundamental to multicellular life and is mediated by a diverse array of cell surface proteins. However, the adhesive interactions ...

A Novel Method for Localizing Reporter Fluorescent Beads Near the Cell Culture Surface for Traction Force Microscopy

PA gels have long been used as a platform to study cell traction forces due to ease of fabrication and the ability to tune their elastic properties. When the substrate is coated with an extracellular matrix protein, cells adhere to the gel and apply forces, causing the gel to deform. The deformation depends on the cell traction and the elastic properties of the gel. If the deformation field of the surface is known, surface traction can be calculated using elasticity theory. Gel deformation is commonly measured by embedding fluorescent marker beads uniformly into the gel. The probes displace as the gel deforms. The probes near the surface of the gel are tracked. The displacements reported by these probes are considered as surface displacements. Their depths from the surface are ignored. This assumption introduces error in traction force evaluations. For precise measurement of cell forces, it is critical for the location of the beads to be known. We have developed a technique that utilizes simple chemistry to confine fluorescent marker beads, 0.1 and 1 &#181;m in diameter, in PA gels, within 1.6 &#956;m of the surface. We coat a coverslip with poly-D-lysine (PDL) and fluorescent beads. PA gel solution is then sandwiched between the coverslip and an adherent surface. The fluorescent beads transfer to the gel solution during curing. After polymerization, the PA gel contains fluorescent beads on a plane close to the gel surface.

Traditional techniques for fabricating polyacrylamide (PA) gels containing fluorescent probes involve sandwiching a gel between an adherent surface and a glass slide. Here, we show that coating this slide with poly-D-lysine (PDL) and fluorescent probes localizes the probes to within 1.6 &#181;m from the gel surface.

Un nuovo metodo per la localizzazione Reporter perline fluorescenti vicino alla superficie coltura cellulare per la trazione microscopia a forza

PA gels have long been used as a platform to study cell traction forces due to ease of fabrication and the ability to tune their elastic properties. When ...

Magnetic Tweezers in a Microplate Format

Mechanobiology describes how the physical forces and mechanical properties of biological material contribute to physiology and disease. Typically, these approaches are limited single-molecule methods, which restricts their availability. To address this need, a microplate assay was developed that enables mechanical manipulation while performing standard biochemical assays. This is achieved using magnets incorporated into a microplate lid to create multiple magnetic tweezers. In this format, force is exerted across biomolecules connected to paramagnetic beads, equivalent to a typical magnetic tweezer. The study demonstrates the application of this tool with FRET-based assays to monitor protein conformations. However, this approach is widely applicable to different biological systems ranging from measuring enzymatic activity through to the activation of signaling pathways in live cells.

Here, we describe the use of a novel microplate assay to enable mechanical manipulation of biomolecules while performing ensemble biochemical assays. This is achieved using a microplate lid modified with magnets to create multiple static magnetic tweezers across the microplate.

Mechanobiology describes how the physical forces and mechanical properties of biological material contribute to physiology and disease. Typically, these ...

Biochimica

High-Speed Magnetic Tweezers for Nanomechanical Measurements on Force-Sensitive Elements

Single-molecule magnetic tweezers (MTs) have served as powerful tools to forcefully interrogate biomolecules, such as nucleic acids and proteins, and are therefore poised to be useful in the field of mechanobiology. Since the method commonly relies on image-based tracking of magnetic beads, the speed limit in recording and analyzing images, as well as the thermal fluctuations of the beads, has long hampered its application in observing small and fast structural changes in target molecules. This article describes detailed methods for the construction and operation of a high-resolution MT setup that can resolve nanoscale, millisecond dynamics of biomolecules and their complexes. As application examples, experiments with DNA hairpins and SNARE complexes (membrane-fusion machinery) are demonstrated, focusing on how their transient states and transitions can be detected in the presence of piconewton-scale forces. We expect that high-speed MTs will continue to enable high-precision nanomechanical measurements on molecules that sense, transmit, and generate forces in cells, and thereby deepen our molecular-level understanding of mechanobiology.

Here, we describe a high-speed magnetic tweezer setup that performs nanomechanical measurements on force-sensitive biomolecules at the maximum rate of 1.2 kHz. We introduce its application to DNA hairpins and SNARE complexes as model systems, but it will be also applicable to other molecules involved in mechanobiological events.

Pinzette magnetiche ad alta velocità per misure nanomeccaniche su elementi sensibili alla forza

Single-molecule magnetic tweezers (MTs) have served as powerful tools to forcefully interrogate biomolecules, such as nucleic acids and proteins, and are ...

Control of Cell Adhesion using Hydrogel Patterning Techniques for Applications in Traction Force Microscopy

Traction force microscopy (TFM) is the main method used in mechanobiology to measure cell forces. Commonly this is being used for cells adhering to flat soft substrates that deform under cell traction (2D-TFM). TFM relies on the use of linear elastic materials, such as polydimethylsiloxane (PDMS) or polyacrylamide (PA). For 2D-TFM on PA, the difficulty in achieving high throughput results mainly from the large variability of cell shapes and tractions, calling for standardization. We present a protocol to rapidly and efficiently fabricate micropatterned PA hydrogels for 2D-TFM studies. The micropatterns are first created by maskless photolithography using near-UV light where extracellular matrix proteins bind only to the micropatterned regions, while the rest of the surface remains non-adhesive for cells. The micropatterning of extracellular matrix proteins is due to the presence of active aldehyde groups, resulting in adhesive regions of different shapes to accommodate either single cells or groups of cells. For TFM measurements, we use PA hydrogels of different elasticity by varying the amounts of acrylamide and bis-acrylamide and tracking the displacement of embedded fluorescent beads to reconstruct cell traction fields with regularized Fourier Transform Traction Cytometry (FTTC).
To further achieve precise recording of cell forces, we describe the use of a controlled dose of patterned light to release cell tractions in defined regions for single cells or groups of cells. We call this method local UV illumination traction force microscopy (LUVI-TFM). With enzymatic treatment, all cells are detached from the sample simultaneously, whereas with LUVI-TFM traction forces of cells in different regions of the sample can be recorded in sequence. We demonstrate the applicability of this protocol (i) to study cell traction forces as a function of controlled adhesion to the substrate, and (ii) to achieve a greater number of experimental observations from the same sample.

Near-UV lithography and traction force microscopy are combined to measure cellular forces on micropatterned hydrogels. The targeted light-induced release of single cells enables a high number of measurements on the same sample.

Controllo dell'adesione cellulare mediante tecniche di modellazione dell'idrogel per applicazioni nella microscopia a forza di trazione

Traction force microscopy (TFM) is the main method used in mechanobiology to measure cell forces. Commonly this is being used for cells adhering to flat ...

Pattern Generation for Micropattern Traction Microscopy

Micropattern traction microscopy allows control of the shape of single cells and cell clusters. Furthermore, the ability to pattern at the micrometer length scale allows the use of these patterned contact zones for the measurement of traction forces, as each micropatterned dot allows for the formation of a single focal adhesion that then deforms the soft, underlying hydrogel. This approach has been used for a wide range of cell types, including endothelial cells, smooth muscle cells, fibroblasts, platelets, and epithelial cells. 
This review describes the evolution of techniques that allow the printing of extracellular matrix proteins onto polyacrylamide hydrogels in a regular array of dots of prespecified size and spacing. As micrometer-scale patterns are difficult to directly print onto soft substrates, patterns are first generated on rigid glass coverslips that are then used to transfer the pattern to the hydrogel during gelation. First, the original microcontact printing approach to generate arrays of small dots on the coverslip is described. A second step that removes most of the pattern to leave islands of small dots is required to control the shapes of cells and cell clusters on such arrays of patterned dots. 
Next, an evolution of this approach that allows for the generation of islands of dots using a single subtractive patterning step is described. This approach is greatly simplified for the user but has the disadvantage of a decreased lifetime for the master mold needed to make the patterns. Finally, the computational approaches that have been developed for the analysis of images of displaced dots and subsequent cell-generated traction fields are described, and updated versions of these analysis packages are provided.

We describe improvements to a standard method for measuring cellular traction forces, based on microcontact printing with a single subtractive patterning step of dot arrays of extracellular matrix proteins on soft hydrogels. This method allows for simpler and more consistent fabrication of island patterns, essential for controlling cell cluster shape.

Generazione di modelli per microscopia a trazione micropattern

Micropattern traction microscopy allows control of the shape of single cells and cell clusters. Furthermore, the ability to pattern at the micrometer ...

Single Cell Durotaxis Assay for Assessing Mechanical Control of Cellular Movement and Related Signaling Events

Durotaxis is the process by which cells sense and respond to gradients of tension. In order to study this process in vitro, the stiffness of the substrate underlying a cell must be manipulated. While hydrogels with graded stiffness and long-term migration assays have proven useful in durotaxis studies, immediate, acute responses to local changes in substrate tension allow focused study of individual cell movements and subcellular signaling events. To repeatably test the ability of cells to sense and respond to the underlying substrate stiffness, a modified method for application of acute gradients of increased tension to individual cells cultured on deformable hydrogels is used which allows for real time manipulation of the strength and direction of stiffness gradients imparted upon cells in question. Additionally, by fine tuning the details and parameters of the assay, such as the shape and dimensions of the micropipette or the relative position, placement, and direction of the applied gradient, the assay can be optimized for the study of any mechanically sensitive cell type and system. These parameters can be altered to reliably change the applied stimulus and expand the functionality and versatility of the assay. This method allows examination of both long term durotactic movement as well as more immediate changes in cellular signaling and morphological dynamics in response to changing stiffness.

Mechanical forces are important for controlling cell migration. This protocol demonstrates the use of elastic hydrogels that can be deformed using a glass micropipette and a micromanipulator to stimulate cells with a local stiffness gradient to elicit changes in cell structure and migration.

Analisi A singola cella Durotaxis per valutare il controllo meccanico del movimento cellulare e gli eventi di segnalazione correlati

Durotaxis is the process by which cells sense and respond to gradients of tension. In order to study this process in vitro, the stiffness of the substrate ...

Biologia

Imaging Molecular Adhesion in Cell Rolling by Adhesion Footprint Assay

Rolling adhesion, facilitated by selectin-mediated interactions, is a highly dynamic, passive motility in recruiting leukocytes to the site of inflammation. This phenomenon occurs in postcapillary venules, where blood flow pushes leukocytes in a rolling motion on the endothelial cells. Stable rolling requires a delicate balance between adhesion bond formation and their mechanically-driven dissociation, allowing the cell to remain attached to the surface while rolling in the direction of flow. Unlike other adhesion processes occurring in relatively static environments, rolling adhesion is highly dynamic as the rolling cells travel over thousands of microns at tens of microns per second. Consequently, conventional mechanobiology methods such as traction force microscopy are unsuitable for measuring the individual adhesion events and the associated molecular forces due to the short timescale and high sensitivity required. Here, we describe our latest implementation of the adhesion footprint assay to image the P-selectin: PSGL-1 interactions in rolling adhesion at the molecular level. This method utilizes irreversible DNA-based tension gauge tethers to produce a permanent history of molecular adhesion events in the form of fluorescence tracks. These tracks can be imaged in two ways: (1) stitching together thousands of diffraction-limited images to produce a large field of view, enabling the extraction of adhesion footprint of each rolling cell over thousands of microns in length, (2) performing DNA-PAINT to reconstruct super-resolution images of the fluorescence tracks within a small field of view. In this study, the adhesion footprint assay was used to study HL-60 cells rolling at different shear stresses. In doing so, we were able to image the spatial distribution of the P-selectin: PSGL-1 interaction and gain insight into their molecular forces through fluorescence intensity. Thus, this method provides the groundwork for the quantitative investigation of the various cell-surface interactions involved in rolling adhesion at the molecular level.

This protocol presents the experimental procedures to perform the adhesion footprint assay to image the adhesion events during fast cell rolling adhesion.