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HORMONES AND SIGNALING

Ectopic expression of caveolin-1 restores physiological contractile response of aged colonic smooth muscle

¹Department of Pediatrics-Gastroenterology and ²Department of Pharmacology, University of Michigan Medical Center, Ann Arbor, Michigan

Submitted 6 February 2007 ; accepted in final form 6 April 2007

Reduced colonic motility has been observed in aged rats with a parallel reduction in acetylcholine (ACh)-induced myosin light chain (MLC₂₀) phosphorylation. MLC₂₀ phosphorylation during smooth muscle contraction is maintained by a coordinated signal transduction cascade requiring both PKC- and RhoA. Caveolae are membrane microdomains that permit rapid and efficient coordination of different signal transduction cascades leading to sustained smooth muscle contraction of the colon. Here, we show that normal physiological contraction can be reinstated in aged colonic smooth muscle cells (CSMCs) upon transfection with wild-type caveolin-1 through the activation of both the RhoA/Rho kinase and PKC pathways. Our data demonstrate that impaired contraction in aging is an outcome of altered membrane translocation of PKC- and RhoA with a concomitant reduction in the association of these molecules with the caveolae-specific protein caveolin-1, resulting in a parallel decrease in the myosin phosphatase-targeting subunit (MYPT) and CPI-17 phosphorylation. Decreased MYPT and CPI-17 phosphorylation activates MLC phosphatase activity, resulting in MLC₂₀ dephosphorylation, which may be responsible for decreased colonic motility in aged rats. Importantly, transfection of CSMCs from aged rats with wild-type yellow fluorescent protein-caveolin-1 cDNA restored translocation of RhoA and PKC- and phosphorylation of MYPT, CPI-17, and MLC₂₀, thereby restoring the contractile response to levels comparable with young adult rats. Thus, we propose that caveolin-1 gene transfer may represent a promising therapeutic treatment to correct the age-related decline in colonic smooth muscle motility.

aging; myosin phosphorylation; RhoA; PKC

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