Purpose: To understand the molecular basis for the known distinct contractile characteristics of trabecular meshwork (TM) and ciliary muscle (CM) cells, the cytoskeleton-enriched protein fractions of the TM and CM cells were isolated and characterized.
Methods: The nonionic surfactant insoluble fraction enriched for cytoskeletal proteins was isolated from human and porcine TM tissue and cells and from CM cells and was characterized by SDS-PAGE, mass spectrometry, and immunoblotting techniques.
Results: The cytoskeleton-enriched protein fraction derived from both human and porcine TM cells contained Plectin 1, Filamin A, non-muscle myosin IIA, clathrin, α-actinin, vimentin, actin, caldesmon, myosin IC, and annexin A2 as major proteins and was noted to exhibit compositional similarity with the cytoskeletal protein fraction isolated from TM tissue. Importantly, the cytoskeletal protein composition of the TM cells was also found to be similar to that noted for CM and vascular endothelial cells. Although the activity of myosin II, a crucial regulator of cellular contraction and a major component of the cytoskeletal protein fraction in TM and CM cells, was regulated predominantly by Rho kinase in both cell types, myosin light chain kinase (MLCK) also appeared to control myosin II activity in CM cells.
Conclusions: These data reveal that the activity of non-muscle myosin II, a critical molecule of cellular contraction, was found to be regulated differentially in TM and CM cells by the Rho kinase and the MLCK pathways despite their compositional similarity in cytoskeletal protein profile.