Keywords

MCP-1, MCPIP, Cardiomyocyte Apoptosis, Diabetes, Obesity, Ischemic Heart Disease

Abstract

Monocyte chemotactic protein-1 (MCP-1) plays a critical role in the development of cardiovascular diseases. How MCP-1 contributes to the development of heart disease is not understood. We present evidence that MCP-1 causes death in cardiac myoblasts, H9c2 by inducing oxidative stress, ER stress and autophagy via a novel Znfinger protein, MCP-1 induced protein (MCPIP). MCPIP expression caused cell death and knockdown of MCPIP, attenuated MCP-1 induced cell death. Expression of MCPIP resulted in induction of iNOS and production of reactive oxygen (ROS). It caused induction of NADPH oxidase subunit phox47 and its translocation to the cytoplasmic membrane. Oxidative stress led to the induction of ER stress markers HSP40, PDI, GRP78 and IRE1α. ER stress lead to autophagy as indicated by beclin-1 induction, cleavage of LC3 to LCII and autophagolysosome formation. Here, MCPIP-induced processes lead to apoptosis as indicated by caspase 3 activation and TUNEL assay. This cell death involved caspase 2 and caspase 12 as specific inhibitors of these caspases prevented MCPIP-induced cell death. Inhibitors of oxidative stress inhibited ER stress, and cell death. Specific inhibitors of ER stress inhibited autophagy and cell death. Inhibition of autophagy inhibited cell death. Microarray analysis showed that MCPIP expression caused induction of a variety of genes known to be involved in cell death. MCPIP caused activation of JNK and p38 and induction of p53 and PUMA. These results collectively suggest that MCPIP induces ROS/RNS production that causes ER stress which leads to autophagy and apoptosis through caspase 2/12 and IRE1α –JNK/p38-p53-PUMA pathway. These results provide the first molecular insights into the mechanism by which elevated MCP-1 levels associated with chronic inflammation may contribute to the development of heart failure. A role for inflammation and MCP-1 in obesity and diabetes has been implicated. Adipogenesis is a key process involved in obesity and associated diseases such as type 2 diabetes. This process involves temporally regulated genes controlled by a set of transcription factors, C/EBPβ, C/EBPδ, C/EBPα, and PPARγ. Currently PPARγ is considered the master regulator of adipogenesis as no known factor can induce adipogenesis without PPARγ. We present evidence that a novel Zn-finger protein, MCPIP, can induce adipogenesis without PPARγ. Classical adipogenesis-inducing medium induces MCP-1 production and MCPIP expression in 3T3-L1 cells before the induction of the C/EBP family of transcription factors and PPARγ. Knockdown of MCPIP prevents their expression and adipogenesis. Treatment of 3T3-L1 cells with MCP-1 or forced expression of MCPIP induces expression of C/EBPβ, C/EBPδ, C/EBPα, PPARγ and adipogenesis without any other inducer. Forced expression of MCPIP induces adipogenesis in PPARγ-/- fibroblasts. Thus, MCPIP is a newly identified master controller that can induce adipogenesis without PPARγ. Heart failure is a major cause of death in diabetic patients. Hyperglycemia is a major factor associated with diabetes that causes cardiomyocyte apoptosis that leads to diabetic cardiomyopathy. Cardiomyoycte apoptosis is a key event involved in the pathophysiological progression of diabetic cardiomyopathy. We have recently found that in ischemic hearts, MCP-1 can induce the zinc-finger protein, MCP-1 induced protein (MCPIP) that causes cardiomyocyte apoptosis. Although there is evidence that inflammation may play a role in diabetic cardiomyopathy, the underlying mechanisms are poorly understood. In this study, we show that treatment of H9c2 cardiomyoblasts and Neonatal Rat Ventricular Myocytes (NRVM) with 28mmol/L glucose concentration results in the induction of both transcript and protein levels of MCP-1 and MCPIP. Inhibition of MCP-1 interaction with CCR2 via specific antibody or with the G-coupled receptor inhibitors propagermanium and pertussis toxin attenuated glucose-induced cell death. Knockdown of MCPIP with specific siRNA yielded similar results. Treatment of cells with 28mmol/L glucose resulted in increased ROS production and phox47 activation. Knockdown of MCPIP attenuated these effects. The increased ROS production observed in H9c2 cardiomyoblasts and NRVM’s resulted in increased ER stress proteins GRP78 and PDI. Knockdown of MCPIP attenuated expression of both GRP78 and PDI. Inhibition of ER stress with TUDC and 4’PBA prevented high glucoseinduced cell death death. Treatment of cells with 28mmol/l glucose resulted in autophagy as determined by an increase in expression of beclin-1 and through increased cleavage of LC3I to LC3II. Knockdown of MCPIP attenuated expression of beclin-1 and prevented cleavage of LC3. Addition of the autophagy inhibitors 3’methyladenine and LY294002 attenuated high glucose-induced H9c2 cardiomyoblast death. We conclude that high glucose-induced H9c2 cardiomyoblast death is mediated via MCP-1 induction of MCPIP that results in ROS that leads to ER stress that causes autophagy and eventual apoptosis.

Notes

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Graduation Date

2009

Advisor

Kolattukudy, Pappachan

Degree

Doctor of Philosophy (Ph.D.)

College

Burnett College of Biomedical Sciences

Department

Biomolecular Science

Degree Program

Biomedical Sciences

Format

application/pdf

Identifier

CFE0002888

URL

http://purl.fcla.edu/fcla/etd/CFE0002888

Language

English

Release Date

November 2010

Length of Campus-only Access

None

Access Status

Doctoral Dissertation (Open Access)

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