Mitophagy is an important type of selective autophagy for specific elimination of damaged mitochondria. PTEN-induced putative kinase protein 1 (PINK1)-catalyzed phosphorylation of ubiquitin (Ub) plays a critical role in the onset of PINK1-Parkin-mediated mitophagy. Phosphatase and tensin homolog (PTEN)-long (PTEN-L) is a newly identified isoform of PTEN, with addition of 173 amino acids to its N-terminus. Here we report that PTEN-L is a novel negative regulator of mitophagy via its protein phosphatase activity against phosphorylated ubiquitin. We found that PTEN-L localizes at the outer mitochondrial membrane (OMM) and overexpression of PTEN-L inhibits, whereas deletion of PTEN-L promotes, mitophagy induced by various mitochondria-damaging agents. Mechanistically, PTEN-L is capable of effectively preventing Parkin mitochondrial translocation, reducing Parkin phosphorylation, maintaining its closed inactive conformation, and inhibiting its E3 ligase activity. More importantly, PTEN-L reduces the level of phosphorylated ubiquitin (pSer65-Ub) in vivo, and in vitro phosphatase assay confirms that PTEN-L dephosphorylates pSer65-Ub via its protein phosphatase activity, independently of its lipid phosphatase function. Taken together, our findings demonstrate a novel function of PTEN-L as a protein phosphatase for ubiquitin, which counteracts PINK1-mediated ubiquitin phosphorylation leading to blockage of the feedforward mechanisms in mitophagy induction and eventual suppression of mitophagy. Thus, understanding this novel function of PTEN-L provides a key missing piece in the molecular puzzle controlling mitophagy, a critical process in many important human diseases including neurodegenerative disorders such as Parkinson's disease.

ACAT1: acetyl-coenzyme A acetyltransferase 1; AHA: L-azidohomoalanine; AO: acidic orange; ATG: autophagy related; CLEAR: Coordinated Lysosomal Expression and Regulation; CQ: chloroquine; CTSB: cathepsin B; HATs: histone acetyltransferases; HDACIs: HDACs inhibitors; HDACs: histone deacetylases; IP: immunoprecipitation; MEFs: mouse embryonic fibroblasts; MS: mass spectrometry; MTOR: mechanistic target of rapamycin (serine/threonine kinase); MTORC1: mechanistic target of rapamycin (serine/threonine kinase) complex 1; PTMs: posttranslational modifications; SAHA: suberoylanilidehydroxamic acid; TFEB: transcription factor EB.

In this study, we investigated the effects of balanced deep-sea water (BDSW) on hyperglycemia and glucose intolerance in high-fat diet (HFD)-induced diabetic C57BL/6J mice. BDSW was prepared by mixing deep-sea water (DSW) mineral extracts and desalinated water to give a final hardness of 500–2000. Mice given an HFD with BDSW showed lowered fasting plasma glucose levels compared to HFD-fed mice. Oral and intraperitoneal glucose tolerance tests showed that BDSW improves impaired glucose tolerance in HFD-fed mice. Histopathological evaluation of the pancreas showed that BDSW recovers the size of the pancreatic islets of Langerhans, and increases the secretion of insulin and glucagon in HFD-fed mice. Quantitative reverse transcription polymerase chain reaction results revealed that the expression of hepatic genes involved in glucogenesis, glycogenolysis and glucose oxidation were suppressed, while those in glucose uptake, β-oxidation, and glucose oxidation in muscle were increased in mice fed HFD with BDSW. BDSW increased AMP-dependent kinase (AMPK) phosphorylation in 3T3-L1 pre- and mature adipocytes and improved impaired AMPK phosphorylation in the muscles and livers of HFD-induced diabetic mice. BDSW stimulated phosphoinositol-3-kinase and AMPK pathway-mediated glucose uptake in 3T3-L1 adipocytes. Taken together, these results suggest that BDSW has potential as an anti-diabetic agent, given its ability to suppress hyperglycemia and improve glucose intolerance by increasing glucose uptake.

Objective: To determine the effects of balanced deep-sea water (BDSW) on adipocyte hypertrophy and liver steatosis in high-fat diet (HFD)-induced obese C57BL/6J mice. Methods: BDSW was prepared by mixing deep-sea water (DSW) mineral extracts and desalinated water. C57BL/6J mice were fed a normal diet or HFD with or without BDSW with different hardness (500, 1000, or 2000) for 20 weeks. Results: BDSW suppressed body weight gain in HFD-fed mice. Histopathologic assays of the fat and liver revealed that BDSW inhibited the increase in adipocyte size and improved severe liver steatosis in HFD-fed mice. BDSW suppressed the expression of adipogenic, lipogenic, lipolytic, and proinflammatory cytokine genes and increased the expression of adipokines and b-oxidation genes in fat. In the liver, BDSW suppressed the expression of genes involved in lipogenesis and cholesterol synthesis, and increased the expression of genes related to b-oxidation. Furthermore, BDSW improved the impaired phosphorylation of IRS-1, LKB1, AMPK, and mTOR in fat and liver tissues of HFD-fed mice. Conclusions: These results suggest that BDSW has potential as an anti-lipidemic agent, given its ability to suppress body weight gain and liver steatosis through the regulation of lipid metabolism by signal molecule activation.

The worldwide prevalence of metabolic diseases, including obesity and diabetes, is increasing. Mitochondrial dysfunction is recognized as a core feature of these diseases. Emerging evidence also suggests that defects in mitochondrial biogenesis, number, morphology, fusion, and fission, contribute to the development and progression of metabolic diseases. Our previous studies revealed that balanced deep-sea water (BDSW) has potential as a treatment for diabetes and obesity. In this study, we aimed to investigate the mechanism by which BDSW regulates diabetes and obesity by studying its effects on mitochondrial metabolism. To determine whether BDSW regulates mitochondrial biogenesis and function, we investigated its effects on mitochondrial DNA (mtDNA) content, mitochondrial enzyme activity, and the expression of transcription factors and mitochondria specific genes, as well as on the phosphorylation of signaling molecules associated with mitochondria biogenesis and its function in C2C12 myotubes. BDSW increased mitochondrial biogenesis in a time and dose-dependent manner. Quantitative real-time PCR revealed that BDSW enhances gene expression of PGC-1α, NRF1, and TFAM for mitochondrial transcription; MFN1/2 and DRP1 for mitochondrial fusion; OPA1 for mitochondrial fission; TOMM40 and TIMM44 for mitochondrial protein import; CPT-1α and MCAD for fatty acid oxidation; CYTC for oxidative phosphorylation. Upregulation of these genes was validated by increased mitochondria staining, CS activity, CytC oxidase activity, NAD+ to NADH ratio, and the phosphorylation of signaling molecules such as AMPK and SIRT1. Moreover, drinking BDSW remarkably improved mtDNA content in the muscles of HFD-induced obese mice. Taken together, these results suggest that the stimulatory effect of BDSW on mitochondrial biogenesis and function may provide further insights into the regulatory mechanism of BDSW-induced anti-diabetic and anti-obesity action.