Boopathi Ettickan, PhD

G-protein-coupled receptors (GPCR) mediated signaling smooth muscle.

Altered contractile-protein expression and increased smooth-muscle cell (SMC) proliferation are characteristics of various disease conditions including hypertension, asthma, and intestine and bladder pathologies. It is well known that smooth-muscle contraction is regulated by the cytosolic Ca2+ concentration and by the Ca2+ sensitivity of myofilaments: the former activates myosin light-chain kinase, and the latter is achieved partly by the inhibition of myosin phosphatase. Calcium released by the intracellular stores binds to calmodulin, and Ca-CaM complex activates MLC kinase that subsequently phosphorylates MLC. The small GTPase RhoA, Rho-associated kinase (the target of RhoA), and Protein kinase C (PKC)-potentiated inhibitory protein of 17 kDa (CPI-17) participate in the calcium sensitization mechanism. The cellular activity of myosin light chain phosphatase (MLCP) determines the agonist-induced force development in smooth muscle. Both calcium- and Ca2+ sensitization- mediated contraction plays role in G-protein signaling during smooth-muscle contraction. The long-term goals of this project are to elucidate the role of GPCR mediated signaling in smooth muscle contraction and proliferation under pathophysiological conditions.

Mitochondria and smooth muscle contraction: Role of desmin cytoskeleton protein.

The second major area of investigation is to understand the role of cytoskeleton proteins, desmin and vimentin in smooth muscle contraction and mitochondrial respiration. In recent years research has shown that desmin and vimentin are involved in signaling pathways and they are the primary factors in facilitating the mechanotransduction. In addition, desmin and vimentin cytoskeleton interacts with mitochondria and possibly modulates respiration. Adenosine triphosphate (ATP) and phosphocreatine are the immediate substrates for processes involved in muscle contraction and relaxation, Ca2+ handling, and phosphorylation. Voltage-dependent anion channel (VDAC) located at the mitochondrial outer membrane play a crucial role in regulating the metabolic and energetic functions of mitochondria and are primarily responsible for the ATP/ADP flux across the outer mitochondrial membrane. The VDAC interact with adenine nucleotide translocase (ANT) to control the mitochondrial membrane permeability to ADP. Mitochondrial desmin and vimentin interacts with the VDAC and this interaction disrupts VDAC/MtCK/ANT complex formation, thereby inhibiting the ATP synthesis and promoting ROS production under pathological conditions in smooth muscle. My long term goal of this project is to elucidate our understanding of the mechanism by which desmin and vimentin induces mitochondrial and muscle dysfunction under pathological conditions in smooth muscle. This could lead to novel molecular targets for therapeutic interventions in smooth muscle pathologies.

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