Neuronal Preconditioning Requires the Mitophagic Activity of C-terminus of HSC70-Interacting Protein

Abstract

C-terminus of HSC70-interacting protein (CHIP, ) is a ubiquitously expressed cytosolic E3-ubiquitin ligase. CHIP-deficient mice exhibit cardiovascular stress and motor dysfunction prior to premature death. This phenotype is more consistent with animal models in which master regulators of autophagy are affected rather than with the mild phenotype of classic E3-ubiquitin ligase mutants. The cellular and biochemical events that contribute to neurodegeneration and premature aging in CHIP KO models remain poorly understood. Electron and fluorescent microscopy demonstrates that CHIP deficiency is associated with greater numbers of mitochondria, but these organelles are swollen and misshapen. Acute bioenergetic stress triggers CHIP induction and re-localization to mitochondria where it plays a role in the removal of damaged organelles. This mitochondrial clearance is required for protection following low-level bioenergetic stress in neurons. CHIP expression overlaps with stabilization of the redox stress sensor PTEN-inducible kinase 1 (PINK1) and is associated with increased LC3-mediated mitophagy. Introducing human promoter-driven vectors with mutations in either the E3 ligase or TPR domains of CHIP in primary neurons derived from CHIP-null animals enhances CHIP accumulation at mitochondria. Exposure to autophagy inhibitors suggests the increase in mitochondrial CHIP is likely due to diminished clearance of these CHIP-tagged organelles. Proteomic analysis of WT and CHIP KO mouse brains (4 male, 4 female per genotype) reveals proteins essential for maintaining energetic, redox and mitochondrial homeostasis undergo significant genotype-dependent expression changes. Together these data support the use of CHIP deficient animals as a predictive model of age-related degeneration with selective neuronal proteotoxicity and mitochondrial failure. Mitochondria are recognized as central determinants of neuronal function and survival. We demonstrate that C-terminus of HSC70-Interacting Protein (CHIP) is critical for neuronal responses to stress. CHIP upregulation and localization to mitochondria is required for mitochondrial autophagy (mitophagy). Unlike other disease-associated E3 ligases such as Parkin and Mahogunin, CHIP controls homeostatic and stress-induced removal of mitochondria. While CHIP deletion results in greater numbers of mitochondria, these organelles have distorted inner membranes without clear cristae. Neuronal cultures derived from animals lacking CHIP are more vulnerable to acute injuries, and transient loss of CHIP renders neurons incapable of mounting a protective response following low-level stress. Together these data suggest that CHIP is an essential regulator of mitochondrial number, cell signaling and survival.

Adverse Effects of Fenofibrate in Mice Deficient in the Protein Quality Control Regulator, CHIP

“…However, several genes involved in the initiation of autophagosome formation including Becn1 , Atg12 , Atg4b , and Map1lc3b [ 51 ] were decreased in CHIP −/− mice when treated with fenofibrate ( Figure 6 d). These data are consistent with the role of CHIP in regulating autophagy-related pathways [ 12 , 46 , 47 , 48 , 49 , 50 ] and the disruption of regulation is more pronounced in conditions that may activate autophagy/mitophagy such as therapies that include fibrates.…”

“…These pathways in the heart are activated by several cardio-protective compounds [ 42 ] including fenofibrate [ 43 , 44 , 45 ]. Moreover, CHIP is known to play an important role in autophagy [ 12 , 46 , 47 , 48 , 49 , 50 ]. To explore the mechanism behind the phenotype observed in CHIP −/− mice, we used qPCR analysis to determine if fenofibrate had differential effects on metabolic or autophagy/mitophagy gene expression in hearts isolated from CHIP −/− versus wild-type mice.…”

Sperm acrosome overgrowth and infertility in mice lacking chromosome 18 pachytene piRNA

“…BAG5, a member of a larger family of proteins, directly interacts with HSP70 and inhibits HSP70-mediated refolding of misfolded proteins 39 . Both STUB1and BAG5 are related to pathways of cellular response to stress and protein kinase and chaperone binding to target proteins for degradation [38][39][40][41] . In addition, it has been reported that diseases associated with BOLL include azoospermia and male infertility 42-44 . We observed significantly increased abundance of STUB1 in Chr18 ∆/∆ testes compared to controls (Fig.…”

Changes in protein function underlies the disease spectrum in patients with CHIP mutations

“…In contrast, SCAR16 patients with cognitive dysfunction and Ubox mutations may benefit from the use of molecular chaperones to prevent the oligmerization of these mutant CHIP proteins. CHIP impacts several cellular pathways, and identifying the CHIP-dependent pathways that may contribute to the specific pathologies in SCAR16, such as necroptosis (28), IGF1 (29), mitophagy (30), autophagy (31,32), or water balance (33), may also uncover therapeutically relevant targets. Additionally, gene therapy approaches might be applicable to SCAR16.…”