Rho/Rock signal transduction pathway is required for MSC tenogenic differentiation

Abstract

Mesenchymal stem cell (MSC)-based treatments have shown promise for improving tendon healing and repair. MSCs have the potential to differentiate into multiple lineages in response to select chemical and physical stimuli, including into tenocytes. Cell elongation and cytoskeletal tension have been shown to be instrumental to the process of MSC differentiation. Previous studies have shown that inhibition of stress fiber formation leads MSCs to default toward an adipogenic lineage, which suggests that stress fibers are required for MSCs to sense the environmental factors that can induce differentiation into tenocytes. As the Rho/ROCK signal transduction pathway plays a critical role in both stress fiber formation and in cell sensation, we examined whether the activation of this pathway was required when inducing MSC tendon differentiation using rope-like silk scaffolds. To accomplish this, we employed a loss-of-function approach by knocking out ROCK, actin and myosin (two other components of the pathway) using the specific inhibitors Y-27632, Latrunculin A and blebbistatin, respectively. We demonstrated that independently disrupting the cytoskeleton and the Rho/ROCK pathway abolished the expression of tendon differentiation markers and led to a loss of spindle morphology. Together, these studies suggest that the tension that is generated by MSC elongation is essential for MSC teno-differentiation and that the Rho/ROCK pathway is a critical mediator of tendon differentiation on rope-like silk scaffolds.

Tendon formation: elongation drives stem cell differentiation

The shape change caused by the elongation of adult stem cells leads the stem cells themselves to commit to tendon differentiation. Working with mesenchymal stem cells, which can be isolated from various tissues, including bone marrow, fat and tendons, a team led by Dr. Hui B. Sun from the Albert Einstein College of Medicine in New York, USA, cultured the cells on a rope-like silk scaffold that allows for attachment, elongation, and growth. The stem cells changed shape to conform to the structure of the silk fibers, triggering biophysical alterations that stimulated the cells to differentiate toward tendon cells. The researchers used various drug inhibitors to demonstrate that the Rho/ROCK regulatory pathway is a critical mediator of this tension-induced transformation. A better understanding of this process could aid in the development of new stem cell-based therapies for tendon regeneration and repair.

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