Mitochondrial Protein Poldip2 Controls VSMC Differentiated Phenotype by O-Linked GlcNAc Transferase-Dependent Inhibition of a Ubiquitin Proteasome System.

Abstract

Rationale: The mitochondrial protein polymerase interacting protein 2 (Poldip2) is required for the activity of the tricarboxylic acid (TCA) cycle. As a consequence, Poldip2 deficiency induces metabolic reprograming with repressed mitochondrial respiration and increased glycolytic activity. Though homozygous deletion of Poldip2 is lethal, heterozygous mice are viable and show protection against aneurysm and injury-induced neointimal hyperplasia, diseases linked to loss of VSMC differentiation. Thus, we hypothesize that the metabolic reprograming induced by Poldip2 deficiency controls VSMC differentiation. Objective: To determine the role of Poldip2-mediated metabolic reprograming in phenotypic modulation of VSMC. Methods and Results: We show that Poldip2 deficiency in vascular smooth muscle in vitro and in vivo induces the expression of the serum response factor (SRF), Myocardin, and MRTFA and dramatically represses KLF4. Consequently, Poldip2-deficient VSMC and mouse aorta express high levels of contractile proteins and, more significantly, these cells do not dedifferentiate nor acquire macrophage-like characteristics when exposed to Cholesterol or PDGF. Regarding the mechanism, we found that Poldip2 deficiency upregulates the hexosamine biosynthetic pathway and OGT-mediated protein O-GlcNAcylation. Increased protein glycosylation causes the inhibition of a nuclear UPS responsible for SRF stabilization and KLF4 repression and is required for the establishment of the differentiated phenotype in Poldip2-deficient cells. Conclusions: Our data show that Poldip2 deficiency induces a highly differentiated phenotype in VSMCs through a mechanism that involves regulation of metabolism and proteostasis. Additionally, our study positions mitochondria-initiated signaling as key element of the VSMC differentiation programs that can be targeted to modulate VSMC phenotype during vascular diseases.