Regulation of contractile activity of cerebral blood vessels and visceral smooth muscle during development and aging
Smooth muscle cells form the wall of blood vessels and visceral hollow organs such as the gastrointestinal tract. Disturbances of contraction and relaxation underlie a number of severe diseases such as hypertension or sepsis associated hypertension, asthma, and premature labor. Such disease but also development and aging have a profound effect of the protein phenotype of the contractile apparatus leading to concomitant changes in the contractile properties. For instance, smooth muscle cells in atherosclerotic vessels adopt an immature synthetic phenotype.
Smooth muscle contraction is dually regulated. The major activating regulatory mechanisms involves the Ca2+-dependent activation of myosin light chain kinase (MLCK) followed by phosphorylation of the regulatory light chains of myosin (MLC20) while dephosphorylation of MLC20 by a specific phosphatase (MLCP) lowers tone. MLCP is a heterotrimeric enzyme consisting of a catalytic, regulatory subunit, called MYPT1, which targets the catalytic subunit to myosin, and a 20kDa subunit of unknown function. MLCP is itself target of a number of protein kinase cascades that modulate its activity thereby increasing Ca2+-sensitivity of contraction by the Rho/Rho-Kinase and the PKC pathways and decreasing by the cAMP/PKA and cGMP/PKG pathways. These modulatory effects are mediated by phosphorylating several serine and threonine residues on MYPT1 and of regulatory peptides, CPI1, which inhibits MLCP and telokin, thought to activate MLCP. The second regulatory mechanism is thin filament filament based and involves caldesmon and regulation of actin filament stability. However, the precise mechanisms of cyclic nucleotide medatiated relaxation and the role of thin filament linked mechanisms are still incompletely understood.
We have a long standing interest in elucidating the mechanisms that mediate cyclic nucleotide induced desensitization of the contractile machinery to the activator Ca2+ thereby inducing relaxation. These second messengers are generated in response to β-adrenergic stimulation or endothelial NO release. We also investigate the role of the thin filament linked protein, caldesmon, putative regulatory affects smooth muscle function as well as how dedifferentiation of smooth muscle cells is prevented.
The relative contribution of these pathways to tone regulation differs between different types of smooth muscle and between fetal/neonatal, adult, and aged smooth muscles and between the synthetic/proliferative and contractile phenotype. To elucidate the interplay of these different regulatory pathways we use different gene-modified animals and investigate the biomechanical properties ex vivo of the different intact and permeabilized smooth muscles in conjunction with phosphorylation determinations of the regulatory proteins.
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