Supporting data for "The Role of Mitochondrial Translocator Protein in Chronic Kidney Disease"

Chronic kidney disease (CKD) is a major public health issue involving multiple risk factors and affecting over 10% of population worldwide. Due to the limitations of current treatments for CKD, it is critical to comprehend the pathogenic mechanisms of the disease and identify novel treatment targets. Tubular atrophy, interstitial fibrosis and inflammation are hallmarks of CKD that have been connected to mitochondrial homeostasis dysregulation. Translocator protein (TSPO) located on the outer mitochondrial membrane is engaged in regulating mitochondrial activities and upregulated in the injured kidney. However, its contribution to CKD and its progression remains unknown. This work aims at investigating the roles of TSPO in progressive CKD by using various experimental models and exploring its potential as a novel therapeutic target.

First, I observed an upregulation of TSPO expression in kidney proximal tubules of CKD patients and different experimental models of CKD. Next, I investigated the effects and mechanisms of TSPO depletion in mouse models of unilateral ureteral obstruction (UUO) and unilateral ischemia-reperfusion injury (UIRI). Both pharmacological inhibition by TSPO antagonist PK11195 and genetic deletion of TSPO in tubule-specific TSPO knockout (KO) mice resulted in amelioration of UUO- or UIRI-induced kidney damage including improvement in morphologic changes, decrease in tubular injury indicators and inflammatory cytokines, and eventually decrease in tubulointerstitial fibrosis (Fn1, α-SMA, vimentin and collagen deposition).

Furthermore, TSPO deficiency in kidney tubules prevented the reduction in mitochondrial mass with an increase in mitochondrial DNA copy number and mitochondrial biogenesis (PGC1α). Additionally, UIRI mice with knockdown of TSPO exhibited improved mitochondrial energy metabolism as evident by reduced glycolysis and upregulated oxidative phosphorylation (OXPHOS), resulting in an increased ATP generation. In vitro, primary renal tubular epithelial cells (RTECs) from TSPO KO mice showed enhanced mitochondrial biogenesis (PGC1α), restored membrane potential and improved mitochondrial energetics (reflected by downregulated glycolytic enzyme HEK2 and upregulated OXPHOS complexes) under hypoxia or TGF-β treatment. I further revealed the possible relationship between TSPO and HEK2 using co-immunoprecipitation (Co-IP) assay in human proximal tubular epithelial (HK-2) cells.

Apart from progressive CKD models, the role of TSPO in kidney injury was also explored in two experimental models of obesity-associated CKD: high-fat diet (HFD)-induced diabetic nephropathy (DN) and type 2 diabetic (T2D) db/db mouse models. Administration of TSPO antagonist PK11195 ameliorated glucose intolerance induced by HFD and mitigated kidney dysfunction (albuminuria), inflammation (TNF-α and interleukins), histopathological abnormalities and lipid accumulation (triglyceride and total cholesterol). Untargeted lipidomic analysis revealed that the lipid composition of HFD kidney was maintained after PK11195 treatment. Notably, PK11195 reversed the increase of phosphatidylcholines (PC), the most abundant phospholipid in kidney cellular membranes, indicating a potential role of TSPO in PC metabolism and CKD progression.

Collectively, my findings indicate a substantial function for TSPO in the development and progression of CKD. TSPO deficiency protected against kidney injury and tubulointerstitial fibrosis by maintaining mitochondria homeostasis. Likewise, blockade of TSPO activity alleviated kidney dysfunction, inflammation and lipid accumulation in obesity-induced CKD models. Targeting TSPO could be a promising technique for avoiding CKD development.