Rajakrishnan Veluthakal, PhD
Department of Opthalmology
Kresge Eye Institute
162,Dorchester drive, Apartment 187
Rochester Hills, Michigan 48307, USA
Dr. Veluthakal is a Seasoned and remarkably astute scientist with extensive knowledge and background in biochemistry, molecular and cell biology, and pathology honed from more than 12 years of experience in the field of diabetes. Display the capability to identify various technical issues in the system flow and recommend sound and efficient resolutions to problems. Possess solid interpersonal skills as exemplified by the ability to work well with professionals of diverse backgrounds and levels and adeptness in liaising between an organization and various academic laboratories.
Diabetes mellitus describes several diseases of abnormal carbohydrate metabolism that are characterized by hyperglycemia resulting from insulin deficiency or defect in insulin action on tissues or even both. These can lead to complications and even death. Both Type 1 [also knows as Insulin dependent diabetes mellitus; IDDM] [autoimmune disorder] and Type 2 [improper utilization of insulin] are equally disastrous. Dr. Rajakrishnan Veluthakal current research focuses on signaling mechanisms underlying the cytokine [e.g., IL-1beta] mediated loss of beta-cell viability, a well accepted model for IDDM, as well as the normal physiological function of pancreatic islet beta-cells [e.g. Glucose-stimulated insulin secretion]. His general research interest in the area of islet biology will enable him to understand the complexities involved in diabetes both type 1 and type 2. Below he will summarize his current research and also outline his future research plan.
Glucose-stimulated insulin secretion, a role for GTP-binding proteins:
Glucose, the most important and most studied secretogue for insulin secretion from pancreatic islets beta cells, uses different signaling pathways to facilitate insulin secretion. The challenge for the cells is to traffic the insulin-laden secretory granules across the cytoskeletal barriers, to the plasma membrane for fusion and release of insulin. The task of trafficking the secretory granules is undertaken by small GTP-binding proteins including Rac1, Cdc42, ARF6, and Rap1. The functional activation of GTP-binding proteins requires the exchange of the bound GDP inactive state for GTP active state which is, carried out by the GDP/GTP exchange factors.
This exchange then facilitates the active GTP-binding proteins to interact with their effector proteins. For inactivation, the GTP-bound form is converted, by the action of the intrinsic GTPase activity, to the GDP-bound form, which then releases the bound effectors. Thus, the activation/inactivation cycle is achieved, and small G proteins serve as molecular switches that transduce an upstream signal to downstream effectors.
The activation of small GTP-binding protein e.g., Rac1, translocation, and effector interaction of these proteins with its upstream regulatory protein Tiam1, an exchange factor for Rac1, in insulin secretion were studied by using different pharmacological, biochemical, and molecular tools [published articles are appended, Diabetes, 56: 204-210, 2007; Diabetes, 54: 3523-3529, 2005 and Am J Physiol Cell Physiol, 292: C1216-1220, 2007]. We were further able to demonstrate the importance of post-translational modifications of these proteins, which is an essential step for the membrane association of these proteins.
Cytokines, the major culprits in islet beta-cell death:
Autoimmune aggression of pancreatic islet beta cells by T cells, macrophages, and dendritic cells leads to secretion of cytokines, IL-1beta, TNFalpha and INFgama, by these cells into the islet micro environment, destroying beta cells, inducing the onset of type 1 diabetes. Although all the three above mentioned cytokines destruct islet beta-cells, the signaling events that they evoke culminating in cell death are diverse. Hence, we mainly focused our attention on IL-1beta-induced beta-cell death. The activation of IL-1beta signaling events leads to functional activation of a transcription factor NF-κB, which induces theexpression of nitric oxide synthase, an enzyme which produces enormous amounts of nitric oxide, leading to cell death.
Our contribution to this signaling pathway was to examine the initial and the distal nuclear events that lead to beta-cell death. We were able to implicate that membrane-associated, cholesterol-enriched caveolae [small flask shaped membrane invaginations] and their key constituent proteins [i.e., caveolin-1] play significant regulatory roles in the IL-1beta signaling pathway in isolated beta-cells. We were able to demonstrate by using mutants of caveolin-1as well as RNAi approaches that tyrosine phosphorylation of caveolin-1 is essential for the early signaling events leading to nitric oxide synthase gene expression and subsequent nitric oxide production publication appended, Diabetes 54: 2576-2585, 2005]. Further we investigated the roles for nuclear lamin-B a structural protein of the nuclear envelope, which has diverse cellular functions including DNA replication, chromatin organization, differentiation, nuclear structural support, and nuclear envelope assembly] in nuclear envelope disassembly, one of the hallmark features of IL-1beta-induced apoptosis of the islet beta- cell
Am J Physiol Cell Physiol, 287: C1152-C1162, 2004.
In this study we were able to demonstrate that nuclear protein lamin-B undergoes phosphorylation and further, is vulnerable to degradation by caspases. The possible mechanism may be due to an increase in the activation of protein kinases that keep the lamin-B in the phosphorylated state or by suppression of lamin phosphatase. We demonstrated recently a unique member of the protein phosphatase 2Ac family; PP4c associated with lamin-B is functionally suppressed by IL-1β which may result in the retention of lamin-B in its phosphorylated state, which a requisite for its degradation byexpression of nitric oxide synthase, an enzyme which produces enormous amounts of nitric oxide, leading to cell death. Our contribution to this signaling pathway was to examine the initial and the distal nuclear events that lead to β-cell death. We were able to implicate that membrane-associated, cholesterol-enriched caveolae [small flask shaped membrane invaginations] and their key constituent proteins [i.e., caveolin-1] play significant regulatory roles in the IL-1β signaling pathway in isolated β-cells. We were able to demonstrate by using mutants of caveolin-1as well as RNAi approaches that tyrosine phosphorylation of caveolin-1 is essential for the early signaling events leading to nitric oxide synthase gene expression and subsequent nitric oxide production [publication appended, Diabetes 54: 2576-2585, 2005]. Further we investigated the roles for nuclear lamin-B a structural protein of the nuclear envelope, which has diverse cellular functions including DNA replication, chromatin organization, differentiation, nuclear structural support, and nuclear envelope assembly] in nuclear envelope disassembly, one of the hallmark features of IL-1beta-induced apoptosis of the islet beta- cell
Am J Physiol Cell Physiol, 287: C1152-C1162, 2004.
In this study we were able to demonstrate that nuclear protein lamin-B undergoes phosphorylation and further, is vulnerable to degradation by caspases. The possible mechanism may be due to an increase in the activation of protein kinases that keep the lamin-B in the phosphorylated state or by suppression of lamin phosphatase. We demonstrated recently a unique member of the protein phosphatase 2Ac family; PP4c associated with lamin-B is functionally suppressed by IL-1β which may result in the retention of lamin-B in its phosphorylated state, which a requisite for its degradation by caspases, leading to the apoptotic demise of the beta-cell Apoptosis, 11: 1401-1411, 2006.
Fatty acid-induced pancreatic beta cell dysfunction is mediated by ceramide:
Abnormal lipid metabolism is a hallmark feature of Type 2 diabetes mellitus. The abnormalities in lipid metabolism, excessive circulating lipid levels, and hyperglycemia contribute to the progressive deterioration of beta cell function. Chronic exposure of isolated β-cells to fatty acids [e.g., palmitate] impairs insulin gene expression, affects expression of the transcription factor pancreatic and duodenal homeobox-1 [PDX-1], and impairs pre-proinsulin mRNA stability and insulin promoter activity. Most of the palmitate effects are mediated by an increase in cellular production of ceramide.We recently demonstrated that ceramide markedly reduced mitochondrial membrane ceramide.We recently demonstrated that ceramide markedly reduced mitochondrial membrane potential in insulin-secreting INS cells, which was followed by a significant accumulation of cytochrome c in the cytosolic compartment. In these studies we were able to demonstrate that ceramide-induced mitochondrial changes are due to activation of a ceramide sensitive protein phosphatase in islet beta-cells
Apoptosis, 10: 841-850, 2005 and Biochem Biophys Res Commun, 348: 649-652, 2006.
These above mentioned studies helped him in understanding the complex signaling cascade associated with 1 pancreatic islet beta-cell death evoked by IL-1beta, 2 helped him to gain an insight into the mechanistic details of the physiological function i.e., insulin secretion of pancreatic islet beta-cells, and 3 added to his knowledge about the complex signaling events associated with pancreatic islet β-cell death due to type 2 diabetes and associated complications.
The National Cancer Institute defines a biomarker as “A biological molecule found in blood, other body fluids, or tissues that is a sign of a normal or abnormal process, or of a condition or disease. A biomarker may be used to see how well the body responds to a treatment for a disease or condition. In the context of diabetes, blood glucose, HbA1c and insulin levels all qualify as biomarkers reflecting endocrine pancreas function, but their shortfall in being truly useful predictors or surrogate endpoints of “abnormal processes or disease” lies in that alteration in their levels are dependent on a variety comorbidities and occur too late in the disease process to be useful sentinels. Because diabetic disease is projected to represent a significant world health care burden there is currently a significant international research effort directed at finding better biomarkers of diabetic disease. Over the past couple of years I have undertaken the challenge of identifying and validating novel biomarkers of diabetic disease suitable for non invasive imaging of beta cell mass (BCM) by evaluating compounds Potential PET ligands that can be of potential use in measuring pancreatic BCM by PET imaging.
Established external Liaison and internal collaborations with academic laboratories to pursue research projects and their fulfillment in a timely fashion. [Wayne State University; 2005-2009, Columbia University; 2009-2011.
Recruited and managed a team of over 35 field staff who collected epidemiological data and biological samples from children enrolled in the study of zinc supplementation strategy and zinc status on preschool children [a collaborative project between Annamalai University, India and The Johns Hopkins Bloomberg School of Public Health, Baltimore, MD] , and coordinated between field staff, clinicians and research lab personals to efficiently run the program and reported to the Director, Center for Micronutrient Research, Annamalai University, India .1998-2001
Independent project design, development and accomplishment of projects, coordinated activities throughout the laboratory, delegate work amongst the various technicians, monitor outputs and keep records of workflow and usage of supplies, supervised the ordering and delivery of new supplies, promote the continuing professional development of staff and oversee the training of trainees, make risk assessments for the laboratory and ensure that the health & safety policy is observed Wayne State University; 2005-2009, Columbia University; 2009-2011.
Reviewed grant proposals and original manuscripts for Journal of Transplantation.
Prepared and presented the research findings at various National and International meetings/seminars and prepared and defended the novel project proposals for funding.
1. Amin R, Chen H, Veluthakal, R ,et al. Mastoparan-induced insulin secretion from insulin-secreting betaTC3 and INS-1 cells: Evidence for its regulation by rho subfamily of G-proteins. Endocrinolog. 2003; 144: 405-418. doi: http://dx.doi.org/10.1210/en.2003-0106
2. Chen, H, Tannous M, Veluthakal R, Amin R, Kowluru A. Novel roles for palmitoylation of Ras in IL-1beta-induced nitric oxide release and caspases-3 activation in insulin secreting beta-cells. Biochemical Pharmacology. 2003; 66: 1681-1694. doi: 10.1016/S0006-2952(03)00549-5
3. Chen H, VeluthakalR, Rengasamy P, Kowluru A. GTP-Binding protein-independent potentiation by mastoparan of IL-1beta-induced nitric oxide release from insulin-secreting HIT-T15 cells. Apoptosis. 2004; 9: 145-148.
4. Jangati, G.R., Veluthakal R, Kowluru A. siRNA-mediated depletion of endogenous protein phosphatase 2Acα markedly attenuates ceramide-activated protein phosphatase activity in insulin-secreting INS-832/13 cells. Biochemical and Biophysical Research Communications. 2006; 348: 649-652. doi: 10.1016/j.bbrc.2006.07.100
5. Jangati GR, Veluthakal R, Susick L, Gruber SA, Kowluru A. Depletion of the catalytic subunit of protein phosphatase- 2A (PP2Ac) markedly attenuates glucose-stimulated insulin secretion in pancreatic beta-cells. Endocrine. 2007; 31: 248-253.
6. Kowluru A, Veluthakal R. Rho GDP-Dissociation Inhibitor GDI plays a negative modulatory role in glucose- stimulated insulin secretion. Diabetes. 2005; 54: 3523-3529. doi: 10.2337/diabetes.54.12.3523
7. Kowluru R, Kowluru A, Veluthakal R, et al. Tiam1-Rac1 signaling axis mediated activation of NADPH oxidase-2 initiates mitochondrial damage in the development of diabetic retinopathy. Diabetologia. doi: 10.1007/s00125-014-3194-z.
8. Kowluru A, Veluthakal R, Kaetzel D. Regulatory roles for nm23/nucleoside diphosphate kinase-like enzymes in insulin secretion from the pancreatic islet beta-cell. Journal of Bioengineering and Biomembranes. 2006; 38: 227-232. doi: 10.1007/s10863-006-9038-x
9. Kowluru A, Veluthakal R, RhodesC, Kamath V, Syed I, Koch B. Protein farnesylation-dependent Raf/extracellular signal related kinase signaling links to cytoskeletal remodeling to facilitate glucose-induced insulin secretion in pancreatic beta-cell. Diabetes. 2010; 59: 967-977. doi: 10.2337/db09-1334.
10. McDonald, P., Veluthakal R, Kaur, H., and Kowluru, A. Biologically active lipids promote trafficking and membrane association of Rac1 in insulin-secreting INS 832/13 cells. American Journal of Physiology – Cell Physiology. 2007; 292: C1216-1220. doi: 10.1152/ajpcell.00467.2006
11. Palanivel R, Veluthakal R, Kowluru A. Regulation by glucose and calcium of the carboxylmethylation of the catalytic subunit of protein phosphatase 2A in insulin-secreting INS-1 cells. American Journal of Physiology – Endocrinology and Metabolism. 2004; 286: E1032-1041. doi: 10.1152/ajpendo.00587.2003
12. Palanivel R, Veluthakal R, McDonald, KowluruA. Further evidence for the regulation of acetyl-CoA carboxylase activity by a glutamate- and magnesium-activated protein phosphatase in the pancreatic beta-cell: defective regulation in the diabetic GK rat islet. Endocrine. 2005; 26: 71-77. doi: 10.1385/ENDO:26:1:071
13. Susick L, Senanayake T, Veluthakal R, Woster P, Kowluru A. A novel histone deacetylase inhibitor prevents IL-1beta-induced metabolic dysfunction in pancreatic beta-cell. Journal of Cellular and Molecular Medicine. 2009; 13: 1877-1885. doi: 10.1111/j.1582-4934.2009.00672.x.
14. Susick L, Veluthakal R, Suresh M, Hadden T, KowluruA. Regulatory roles for histone deacetylation in IL-1beta- induced nitric oxide release in pancreatic beta-cell. Journal of Cellular and Molecular Medicine. 2007; 12: 1571-1583. doi: 10.1111/j.1582-4934.2007.00171.x
15. Kowluru R, Kowluru A, Veluthakal R, et al. TIAM1-RAC1 signalling axis-mediated activation of NADPH oxidase-2 initiates mitochondrial damage in the development of diabetic retinopathy. Diabetologia. 2014; 57: 1047-1056. doi: 10.1007/s00125-014-3194-z.
16. Tannous M, Veluthakal R, Amin R, Kowluru A. IL-1beta-induced nitric oxide release from insulin secreting beta-cells: Further evidence for the involvement of GTP-binding proteins. Diabetes and Metabolism. 2002; 28: 3S78-3S84.
17. Veluthakal R, Harris P. In vivo beta-cell imaging with VMAT 2 ligands-current state-of-the-art and future perspective. Current Pharmaceutical Design. 2010; 16: 568-1581. doi: 10.2174/138161210791164180
18. Veluthakal, R. Kowluru A. Post translational modifications of nuclear lamin: Possible implication in survival and demise of pancreatic beta-cell. Recent Research Developments in Biophysics and Biochemistry. 2003; 3: 519-529.
19. Veluthakal R, Amin R, Kowluru, A. IL-1beta- induces posttranslational carboxymethylation and alterations in subnuclear distribution of lamin B in insulin-secreting RINm5F cells. American Journal of Physiology -Cell Physiology. 2 004; 287: C1152-1162. doi: 10.1152/ajpcell.00083.2004
20. Veluthakal R, Chvyrkova I. Tannous, M,et al. Essential Role for Membrane Lipid Rafts in Interleukin-1beta-Induced Nitric Oxide Release from insulin-secreting cells: Potential regulation by caveolin-1. Diabetes. 2005; 54: 2576-2585. doi: 10.2337/diabetes.54.9.2576
21. Veluthakal R, Jangati GR, and Kowluru A. IL-1beta-induced iNOS expression, NO release and loss in metabolic cell viability are resistant to inhibitors of ceramide synthase and sphingomyelinase in INS 832/13 cells. Journal of the Pancreas. 2006; 7: 596-601.
22. Veluthakal R, Kaetzel D, Kowluru A. Nm23-H1 Regulates Glucose-Stimulated Insulin Secretion in Pancreatic beta-Cells via Arf6-Rac1 Signaling Axis. Cellular Physiology and Biochemistry. 2013; 32: 533-541. doi: 10.1159/000354457.
23. Veluthakal R, Kaur H, Goalstone M, Kowluru A. Dominant negative alpha-subunit of farnesyl- and geranyl-transferase inhibits glucose-stimulated insulin secretion from insulin-secreting INS-cells. Diabetes. 2007; 56: 204-210.
24. Veluthakal R, Kha I, Tannous M, Kowluru A. Functional inactivation by interleukin-1 of glyceraldehyde-3- phosphate dehydrogenase in insulin-secreting cells. Apoptosis. 2002; 7: 241-246.
25. Veluthakal R, Madathilparambil S, McDonald P, Olson L, Kowluru A. Regulatory roles for Tiam1, a guanine nucleotide exchange factor for Rac1, in glucose-stimulated insulin secretion in pancreatic beta-cell. Biochemical Pharmacology. 2009; 77: 101-113. doi: 10.1016/j.bcp.2008.09.021.
26. Veluthakal R, Palanivel R, Zhao , McDonald P, Gruber S, Kowluru A. Ceramide induces mitochondrial abnormalities in insulin-secreting INS-1 cells: Potential mechanisms underlying ceramide-mediated metabolic dysfunction of the beta-cell. Apoptosis. 2005; 10: 841-850. doi: 10.1007/s10495-005-0431-4
27. Veluthakal R, Suresh MV, Kowluru A. Down-regulation of expression and function of nucleoside diphosphate kinase in insulin-secreting beta-cell under in vitro conditions of glucolipotoxicity. Molecular and Cellular Biochemistry. 2009; 329: 121-129. doi: 10.1007/s11010-009-0113-6.
28. Veluthakal R, Wadzinski B, Kowluru A. Selective inhibition of nuclear protein phosphatase 4 by IL-1beta-in insulin- secreting INS-1 cells. Apoptosis. 2006; 11: 1401-1411.