Abstract 19822: Arterial Calcification Can Be Inhibited via Stress Protein Induction Through a PPAR-dependent Pathway

Abstract

Introduction: Cardiovascular disease occurs prematurely in chronic inflammatory conditions such as Chronic Kidney Disease (CKD) and unfortunately, remains the leading cause of death in these patients. Vascular calcification (VC) is a significant contributor to cardiovascular mortality in CKD patients with the sequela of arterial hardening, congestive heart failure and sudden cardiac death. We recently reported that heat shock protein 72 (HSP72) when inducted, can inhibit the development of VC. Hypothesis: We hypothesize that HSP72 exerts its vasculo-protective effects by functioning as a molecular chaperon for peroxisome proliferator-activated receptor γ (PPARγ). Methods: We developed an in vitro long-term calcification model using HA-SMCs treated with calcification medium (CM) containing 5mM CaCl2 and 5mM β-glycerophosphate for 21 days. Cells were subjected to heat shock treatment at 43°C for 30 minutes daily to induce HSP72. Calcification was assessed qualitatively by alizarin red staining and quantitatively by the arsenazo III method. Results: Our results show that inducible HSP72 is significantly expressed following heat shock treatment in HA-SMCs. Induction of HSP72 inhibited the development of VC in our long-term calcification model and these effects were abolished by HSP72 siRNA, in vitro. We next showed that HSP72 formed a protein-protein complex with PPARγ by co-immunoprecipitation. Expression of both these proteins was down-regulated in calcific HA-SMCs and their gene expression was down regulated in atherosclerotic human arteries. Furthermore, we found that the PPARγ inhibitor, FABP4 (fatty acid binding protein-4) which function as an atherosclerosis promoter was up-regulated in calcified human arteries. Lastly, induction of HSP72 restored expression of the HSP72-PPARγ complex and inhibited upregulation of FABP4 with reduction in calcification in our in vitro calcification model. These vasculo-protective effects were abolished by HSP72 siRNA. Conclusion: HSP72 is a powerful inhibitor of VC and exerts its vasculo-protective effects by functioning as a molecular chaperon to stabilize PPARγ and regulate the PPARγ-FABP4 pathway. We suggest treatment strategies involving induction of HSP72 as a new approach to inhibit VC.