Dr. Ramaswamy Sharma joined the Department of Cell Systems and Anatomy in 2010. His doctoral studies at Wayne State University School of Medicine (molecular neuroscience) were focused on elucidating mechanisms underlying conformational disorders characterized by: accumulation of misfolded proteins in the endoplasmic reticulum (ER), induction of ER stress, activation of the Unfolded Protein Response (UPR) and apoptosis induced by caspase-12. As a Research Fellow and as an Asst. Research Investigator at Forsyth Institute and at Harvard School of Dental Medicine, Boston, MA, he continued his research on stress-based signaling pathways, using dental enamel as a paradigm. His current research characterizes the role of caspase-2 in mesenchymal stromal/stem cells during normal bone development and in aging-related osteoporosis.
Osteoporosis currently affects approximately 10 million Americans; another 34 million are osteopenic. A direct consequence of bone fragility is an increased risk of painful fractures that are associated with functional disabilities, increased mortality at older ages, and a huge cost burden on families and health providers. Current treatment of osteoporotic patients mostly involves fracture prevention; there are few viable treatments after fractures have occurred. Therefore, an understanding of the molecular and cellular mechanisms underlying osteoporosis and subsequent development of novel therapies are required.
Caspase-2, a cysteine-aspartate protease, is the most conserved caspase across species. It has been shown to play an apoptotic role during mitochondrial oxidative stress; however, non-enzymatic and non-apoptotic roles for caspase-2 have also been reported. Mice lacking caspase-2 exhibit increased oxidative stress, perhaps due to decreased apoptosis of oxidatively-damaged cells. These mice also demonstrate shortened maximum lifespan, impaired hair re-growth, reduced body fat content and osteopenia at older ages. We hypothesize that these pleiotropic phenotypes could arise due to altered properties of mesenchymal stromal/stem cells (MSCs) in the absence of caspase-2. MSCs are pluripotent cells that can differentiate into several cell types, including bone-forming osteoblasts, fat-forming adipocytes and cartilage-forming chondrocytes. MSCs are present in various niches within the bone marrow, fat, muscle, liver and hair follicles. We propose that caspase-2 deficiency-associated bone loss could occur due to decreased osteogenic differentiation and function as well as due to inefficient clearance of oxidatively damaged MSCs. We are currently developing conditional knockouts of caspase-2 in the limb bud mesenchyme to characterize the role of caspase-2 in MSC proliferation, differentiation and/or function as well as in oxidative stress-induced apoptosis. The long-term goal of our research is to identify molecules and pathways for diagnosis and therapy of osteoporosis using MSC-based treatments.
Caspase-2 is expressed in bone
(A) Immunohistochemistry for caspase-2 (brown) shows that it is present in bone marrow (yellow arrows) and osteoblasts (red arrows)
(B) Immunofluorescence for caspase-2 (green) in isolated mesenchymal stromal/stem cells; nuclei are stained blue
Sharma R, Tsuchiya M, Tannous BA, Bartlett JD. (2011) Measurement of fluoride-induced endoplasmic reticulum stress using Gaussia luciferase. Methods Enzymol. 2011;491:111-25.
Sharma R, Tye CE, Arun A, MacDonald D, Chatterjee A, Abrazinski T, Everett ET, Whitford GM, Bartlett JD. (2011)Assessment of dental fluorosis in Mmp20 +/- mice. J Dent Res. 2011 Jun;90(6):788-92.
Sharma R, Tsuchiya M, Skobe Z, Tannous BA, Bartlett JD. (2010) The acid test of fluoride: how pH modulates toxicity. PLoS One. 2010 May 28;5(5):e10895.
Sharma R, Tsuchiya M, Bartlett JD. (2008) Fluoride induces endoplasmic reticulum stress and inhibits protein synthesis and secretion. Environ Health Perspect. 2008 Sep;116(9):1142-6.
Sharma R, Gow A. (2007) Minimal role for caspase 12 in the unfolded protein response in oligodendrocytes in vivo.J Neurochem. 2007 May;101(4):889-97.