Sita Somara, PhD
Sita Somara, Ph.D., Assistant ProfessorDr. Sita Somara received her PhD in Biochemistry from Sri Krishnadevaraya University, Anantapur, India. During her PhD, she was a visiting scholar to Braunschweig, Germany on DAAD fellowship. She joined as research associate in University of Maryland, Baltimore, and moved to Wayne State University as senior research associate. Later she joined University of Michigan in 2002 and has been working with Dr. Khalil N. Bitar in GI molecular motor laboratory. In 2011, she joined Wake Forest Institute for Regenerative Medicine as Assistant Professor.
SYNOPSIS OF AREA OF INTEREST: Dr. Somara’s research focuses on the understanding the basis of gastrointestinal smooth muscle contraction and relaxation. Dr. Somara has continuing interest in studying the myogenic and neurogenic contribution to motility disorders associated with aging as well as to inflammatory bowel disorder. Her goal is to understand the underlying cause for motility disorders and develop novel regenerative medicine approaches to remedy.
DETAILED AREA OF INTEREST:
Gastrointestinal motility is synchronized action of smooth muscle layers controlled by intrinsic and extrinsic innervation. Contraction and relaxation of smooth muscle is regulated at thin/thick filament level as well as at signaling level. The main areas of research are (1) characterization of thin-filament and thick-filament mediated regulation of smooth muscle contraction and relaxation; (2) elucidation of signal transduction pathways mediating smooth muscle contraction and relaxation; (3) explore the cause for sluggish colonic motility in aged colon; (4) factors responsible for dysmotility associated with inflammatory bowel disorder such as crohn’s disease and ulcerative colitis; (5) bioengineering of smooth muscle innervated constructs to provide a regenerative medicine approach as remedy for dysmotility or as a replacement colon.
Contraction of smooth muscle is associated with influx of calcium and is initiated with phosphorylation of regulatory myosin light chain (MLC20). Regulation of contraction and relaxation occurs at thick-filament (myosin), thin-filament (actin and actin-associated proteins), and signal transduction level. At thick-filament level: Myosin light chain kinase (MLCK) phosphorylates MLC20 while myosin light chain phosphatase (MLCP) dephosphorylates phosphorylated MLC20. Phosphorylation of MLC20 leads to contraction while dephosphorylation leads to relaxation. Balance between the activities of MLCK and MLCP determines contraction and relaxation status of smooth muscle. At thin-filament level: Different contractile proteins are involved in mediating the interaction of actin with myosin which leads to contraction or relaxation. Caldesmon and Tropomyosin are two major contractile proteins that have been shown to play an important role in blocking the interaction of actin with myosin. Caldesmon holds tropomyosin on actin while tropomyosin blocks the myosin binding sites on actin and inhibits actomyosin interaction. Upon initiation of contraction, caldesmon is phosphorylated which releases its hold on tropomyosin that gets phosphorylated and slides over actin filament exposing the myosin binding sites This allows myosin to bind to actin resulting in contraction. Research from the lab has shown the crucial role of phosphorylated HSP27 in sliding of tropomyosin on actin filaments. Further research on tropomyosin showed that tropomyosin interacts with signaling molecule protein kinase C alpha and is phosphorylated during colonic smooth muscle contraction. Further research is focused on elucidating the sequence of events leading to contraction and relaxation of smooth muscle.At signal transduction level: Lab has previously reported that HSP27 also appears to play an important role in smooth muscle contraction by forming a link between signaling cascade and contractile machinery. HSP27 colocalizes with the contractile proteins actin, myosin, caldesmon, and tropomyosin as well as associates with the signaling proteins PKCα and RhoA presenting its dual roles. Lab research has shown that contraction associated translocation of PKCα and RhoA is dependent on phosphorylation of HSP27. PKCα and RhoA play crucial role in contraction by inhibiting MLCP that dephosphorylates phosphorylated MLC20. Caveolae are the micro-invaginations on the smooth muscle plasma membranes involved with sequestration and activation of signaling molecules.
Present ongoing research is focused on identifying the impairment in myogenic and neurogenic component at different levels of regulation of smooth muscle contraction and relaxation that are the cause of colonic dysmotility associated with aging and/or inflammatory bowel disease. Further research focuses on different approaches to remedy the dysmotility specifically using (i) regenerative medicine approach by bioengineering innervated smooth muscle constructs and (ii) dietary changes approach. The overall aim is to translate laboratory discoveries into clinical technologies that can improve GI health.