Biomedical subjects

Maureen A Griffin

Publications and source records attributed to Maureen A Griffin.

4 recordsLinked to original sources

PubMed2005

gamma-Sarcoglycan deficiency increases cell contractility, apoptosis and MAPK pathway activation but does not affect adhesion.

The functions of gamma-sarcoglycan (gammaSG) in normal myotubes are largely unknown, however gammaSG is known to assemble into a key membrane complex with dystroglycan and its deficiency is one known cause of limb-girdle muscular dystrophy. Previous findings of apoptosis from gammaSG-deficient mice are extended here to cell culture where apoptosis is seen to increase more than tenfold in gammaSG-deficient myotubes compared with normal cells. The deficient myotubes also exhibit an increased contractile prestress that results in greater shortening and widening when the cells are either lightly detached or self-detached. However, micropipette-forced peeling of single myotubes revealed no significant difference in cell adhesion. Consistent with a more contractile phenotype, acto-myosin striations were more prominent in gammaSG-deficient myotubes than in normal cells. An initial phosphoscreen of more than 12 signaling proteins revealed a number of differences between normal and gammaSG(-/-) muscle, both before and after stretching. MAPK-pathway proteins displayed the largest changes in activation, although significant phosphorylation also appeared for other proteins linked to hypertension. We conclude that gammaSG normally moderates contractile prestress in skeletal muscle, and we propose a role for gammaSG in membrane-based signaling of the effects of prestress and sarcomerogenesis.

Animals↗

PubMed2004

Adhesion-contractile balance in myocyte differentiation.

Tissue cells generally pull on their matrix attachments and balance a quasi-static contractility against adequate adhesion, but any correlation with and/or influence on phenotype are not yet understood. Here, we begin to demonstrate how differentiation state couples to actomyosin-based contractility through adhesion and substrate compliance. Myotubes are differentiated from myoblasts on collagen-patterned coverslips that allow linear fusion but prevent classic myotube branching. Post-fusion, myotubes adhere to the micro-strips but lock into a stress fiber-rich state and do not differentiate significantly further. In contrast, myotubes grown on top of such cells do progress through differentiation, exhibiting actomyosin striations within one week. A compliant adhesion to these lower cells is suggested to couple to contractility and accommodate the reorganization needed for upper cell striation. Contractility is assessed in these adherent cells by mechanically detaching one end of the myotubes. All myotubes, whether striated or not, shorten with an exponential decay. The cell-on-cell myotubes relax more, which implies a greater contractile stress. The non-muscle myosin II inhibitor blebbistatin inhibits relaxation for either case. Myotubes in culture are thus clearly prestressed by myosin II, and this contractility couples to substrate compliance and ultimately influences actomyosin striation.

Actins↗

PubMed2004

Myotubes differentiate optimally on substrates with tissue-like stiffness: pathological implications for soft or stiff microenvironments.

Contractile myocytes provide a test of the hypothesis that cells sense their mechanical as well as molecular microenvironment, altering expression, organization, and/or morphology accordingly. Here, myoblasts were cultured on collagen strips attached to glass or polymer gels of varied elasticity. Subsequent fusion into myotubes occurs independent of substrate flexibility. However, myosin/actin striations emerge later only on gels with stiffness typical of normal muscle (passive Young's modulus, E approximately 12 kPa). On glass and much softer or stiffer gels, including gels emulating stiff dystrophic muscle, cells do not striate. In addition, myotubes grown on top of a compliant bottom layer of glass-attached myotubes (but not softer fibroblasts) will striate, whereas the bottom cells will only assemble stress fibers and vinculin-rich adhesions. Unlike sarcomere formation, adhesion strength increases monotonically versus substrate stiffness with strongest adhesion on glass. These findings have major implications for in vivo introduction of stem cells into diseased or damaged striated muscle of altered mechanical composition.

Acrylic Resins↗

PubMed2004

Patterning, prestress, and peeling dynamics of myocytes.

As typical anchorage-dependent cells myocytes must balance contractility against adequate adhesion. Skeletal myotubes grown as isolated strips from myoblasts on micropatterned glass exhibited spontaneous peeling after one end of the myotube was mechanically detached. Such results indicate the development of a prestress in the cells. To assess this prestress and study the dynamic adhesion strength of single myocytes, the shear stress of fluid aspirated into a large-bore micropipette was then used to forcibly peel myotubes. The velocity at which cells peeled from the surface, V(peel), was measured as a continuously increasing function of the imposed tension, T(peel), which ranges from approximately 0 to 50 nN/ micro m. For each cell, peeling proved highly heterogeneous, with V(peel) fluctuating between 0 micro m/s ( approximately 80% of time) and approximately 10 micro m/s. Parallel studies of smooth muscle cells expressing GFP-paxillin also exhibited a discontinuous peeling in which focal adhesions fractured above sites of strong attachment (when pressure peeled using a small-bore pipette). The peeling approaches described here lend insight into the contractile-adhesion balance and can be used to study the real-time dynamics of stressed adhesions through both physical detection and the use of GFP markers; the methods should prove useful in comparing normal versus dystrophic muscle cells.

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