Hung-Yu Sun

Aims/hypothesis Ectopic lipid accumulation in renal tubules induces lipotoxicity and contributes to the progression of diabetic kidney disease (DKD). Apolipoprotein J (ApoJ), a glucose-regulated, liver-derived molecular chaperone, is implicated in systemic metabolic homeostasis. This study aimed to investigate the pathophysiological role of ApoJ in the development of DKD. Methods Spearman’s r analysis was used to evaluate the association between circulating ApoJ concentrations and renal function in a cohort of 201 individuals with type 2 diabetes mellitus. The pathways were identified by proteomic analyses and subsequently validated using gain- and loss-of-function approaches in proximal tubular epithelial HK2 cells, tissue-specific ApoJ-knockout mice and additional mouse models of DKD. Results In individuals with type 2 diabetes, circulating ApoJ concentrations were positively associated with indices of renal dysfunction. In murine models of DKD, elevated renal ApoJ was accompanied by increased lipid accumulation and structural kidney injury. Mechanistic studies revealed that ApoJ inhibited FBW7-mediated ubiquitination of mammalian target of rapamycin (mTOR), thereby enhancing mTOR interaction with transcription factor EB (TFEB) in HK2 cells under conditions of nutrient excess, leading to lipid imbalance and renal fibrosis. Hepatocyte-specific deletion of ApoJ eliminated circulating ApoJ, prevented its accumulation in renal tubules and ameliorated diabetic kidney injury. Furthermore, pharmacological blockade with the ApoJ antagonist MK53 reactivated the TFEB–autophagy pathway, restored lipid homeostasis and reduced renal damage in diabetic mice. Conclusions/interpretation Our findings highlight a liver-to-kidney interorgan transfer of pathogenetic ApoJ in diabetic kidney injury and suggest that MK53 represents a potential therapeutic strategy for DKD. Graphical Abstract

Background/Objectives: Type 2 diabetes mellitus (T2DM) is a major metabolic disorder and is frequently accompanied by liver steatosis. Apolipoprotein J (ApoJ) is a glucose-regulated molecular chaperone that has been implicated in hepatic lipid deposition under nutrient overload. This study aimed to investigate the role of hepatocyte-specific ApoJ deletion in hepatic metabolism under diabetic conditions. Methods: A T2DM mouse model with hepatocyte-specific ApoJ knockout (HKO) was established through a high-fat diet combined with streptozotocin injection. Hepatic metabolic profiles were analyzed using untargeted metabolomics with UHPLC–MS/MS. Differential metabolites were subjected to KEGG pathway and Sankey diagram analyses to identify biologically relevant pathways. Results: In total, 140 metabolites showed significant differential abundance in HKO mouse liver, primarily encompassing organic acids and derivatives as well as lipids and lipid-like molecules. KEGG analysis revealed that ApoJ deletion enhanced pathways related to vitamin digestion and absorption, thiamine metabolism, amino acid biosynthesis, lysine degradation, and 2-oxocarboxylic acid metabolism. In contrast, pathways associated with galactose metabolism, cysteine and methionine metabolism, purine metabolism, and the pentose phosphate pathway were suppressed. Sankey diagram analysis further demonstrated that ApoJ deletion markedly reshapes hepatic metabolic networks in T2DM. Conclusions: Given the central role of hepatic dysmetabolism in the pathogenesis of diabetes and its complications, targeting ApoJ may represent a promising therapeutic approach for restoring hepatic metabolic homeostasis and preventing diabetes-associated steatosis.

Background/Objectives: Metabolic dysfunction-associated steatotic liver disease (MASLD) is highly prevalent worldwide and represents a growing healthcare challenge due to its risk of progression and association with metabolic comorbidities. Extracellular vesicles (EVs), nanosized membrane-bound particles mediating intercellular communication, have emerged as candidate biomarkers in multiple diseases. This study aimed to characterize serum EV profiles in MASLD patients, stratified into obese and lean groups using a body mass index cutoff of 23 for Asians. Methods: We enrolled 170 MASLD patients, 83 obese (median age 50, range 20–80) and 87 lean (median age 50, range 20–87), along with 57 non-MASLD controls (median age 44, range 21–86). Serum EV concentrations and particle sizes were quantified using nanoparticle tracking analysis and correlated with clinical and laboratory parameters. EV cargo proteins, including tetraspanins (CD9, CD63) and lipid droplet-associated perilipins (PLIN2, PLIN3), were assessed by Western blotting. Results: Obese MASLD patients displayed marked biochemical abnormalities, whereas lean MASLD patients showed levels comparable to non-MASLD controls. Nevertheless, serum EV concentrations were elevated in both the obese and lean MASLD groups. Importantly, in lean MASLD, EV levels correlated strongly with disruptions in lipid and glycemic homeostasis. Furthermore, a reduction in the PLIN3/CD63 ratio was observed in EVs isolated from lean MASLD patients. Conclusions: Circulating EVs are elevated in both obese and lean MASLD, but lean patients demonstrate a distinctive decrease in the EV PLIN3/CD63 ratio. These findings highlight the potential of EV profiling to uncover disease heterogeneity and to inform risk stratification in MASLD.

Ectopic lipid accumulation in renal tubules leads to lipotoxicity and exacerbates the progression of diabetic kidney disease (DKD). Apolipoprotein J (ApoJ) functions as a stress-induced molecular chaperone and participates in lipid homeostasis. As a hepatocyte-secreted entity, the involvement of ApoJ in the pathogenesis of extrahepatic organs remains poorly understood. Herein, serum ApoJ levels have been found to correlate with glycemic profiles, renal function parameters, and disease progression in individuals with Type-II diabetes. Accumulation of ApoJ in renal tubules was observed in mouse models of DKD and confirmed pathologically by renal overexpression of ApoJ in db/db mice. Under nutrient overload, ApoJ disrupts lipid and redox homeostasis and promotes epithelial-mesenchymal transition of proximal tubular cells by facilitating mTOR and transcription factor EB (TFEB) interaction. Consequently, targeting ApoJ promotes TFEB activation, restores autophagy, and alleviates renal injuries. By using tissue-specific knockout mice, we further demonstrated that the liver serves as a major source contributing to the ApoJ accumulated in renal tubules. Finally, the application of an MK53 peptide antagonizes ApoJ chaperone activity, thereby relieving disease progression of DKD. In summary, these findings suggest that ApoJ promotes diabetic renal pathogenesis through mTOR-TFEB-autophagy axis, and MK53 peptide emerges as a novel therapeutic strategy against DKD.

Background and Aims: Overnutrition-induced activation of mammalian target of rapamycin (mTOR) dysregulates intracellular lipid metabolism and contributes to hepatic lipid deposition. Apolipoprotein J (ApoJ) is a molecular chaperone and participates in pathogen-induced and nutrient-induced lipid accumulation. This study investigates the mechanism of ApoJ-regulated ubiquitin-proteasomal degradation of mTOR, and a proof-of-concept ApoJ antagonist peptide is proposed to relieve hepatic steatosis. Approach and Results: By using omics approaches, upregulation of ApoJ was found in high-fat medium-fed hepatocytes and livers of patients with NAFLD. Hepatic ApoJ level associated with the levels of mTOR and protein markers of autophagy and correlated positively with lipid contents in the liver of mice. Functionally, nonsecreted intracellular ApoJ bound to mTOR kinase domain and prevented mTOR ubiquitination by interfering FBW7 ubiquitin ligase interaction through its R324 residue. In vitro and in vivo gain-of-function or loss-of-function analysis further demonstrated that targeting ApoJ promotes proteasomal degradation of mTOR, restores lipophagy and lysosomal activity, thus prevents hepatic lipid deposition. Moreover, an antagonist peptide with a dissociation constant (Kd) of 2.54 µM interacted with stress-induced ApoJ and improved hepatic pathology, serum lipid and glucose homeostasis, and insulin sensitivity in mice with NAFLD or type II diabetes mellitus. Conclusions: ApoJ antagonist peptide might be a potential therapeutic against lipid-associated metabolic disorders through restoring mTOR and FBW7 interaction and facilitating ubiquitin-proteasomal degradation of mTOR.

Tamoxifen is the most widely used hormone therapy in estrogen receptor-positive (ER+) breast cancer, which accounts for approximately 70% of all breast cancers. Although patients who receive tamoxifen therapy benefit with respect to an improved overall prognosis, resistance and cancer recurrence still occur and remain important clinical challenges. A recent study identified TAR (HIV-1) RNA binding protein 2 (TARBP2) as an oncogene that promotes breast cancer metastasis. In this study, we showed that TARBP2 is overexpressed in hormone therapy-resistant cells and breast cancer tissues, where it enhances tamoxifen resistance. Tamoxifen-induced TARBP2 expression results in the desensitization of ER+ breast cancer cells. Mechanistically, tamoxifen post-transcriptionally stabilizes TARBP2 protein through the downregulation of Merlin, a TARBP2-interacting protein known to enhance its proteasomal degradation. Tamoxifen-induced TARBP2 further stabilizes SOX2 protein to enhance desensitization of breast cancer cells to tamoxifen, while similar to TARBP2, its induction in cancer cells was also observed in metastatic tumor cells. Our results indicate that the TARBP2-SOX2 pathway is upregulated by tamoxifen-mediated Merlin downregulation, which subsequently induces tamoxifen resistance in ER+ breast cancer.

Vitamin D has been identified as an innate anti-hepatitis C virus (HCV) agent but the possible mechanisms for this issue remain unclear. Here, we clarified the mechanisms of calcitriol-mediated inhibition of HCV infection. Calcitriol partially inhibited HCV infection, nitric oxide (NO) release and lipid accumulation in Huh7.5 human hepatoma cells via the activation of vitamin D receptor (VDR). When cells were pretreated with the activators of peroxisome proliferator-activated receptor (PPAR)-α (Wy14643) and -γ (Ly171883), the calcitriol-mediated HCV suppression was reversed. Otherwise, three individual stimulators of PPAR-α/β/γ blocked the activation of VDR. PPAR-β (linoleic acid) reversed the inhibition of NO release, whereas PPAR-γ (Ly171883) reversed the inhibitions of NO release and lipid accumulation in the presence of calcitriol. The calcitriol-mediated viral suppression, inhibition of NO release and activation of VDR were partially blocked by an inhibitor of endoplasmic reticulum-associated degradation (ERAD), kifunensine. Furthermore, calcitriol blocked the HCV-induced expressions of apolipoprotein J and 78 kDa glucose-regulated protein, which was restored by pretreatment of kifunensine. These results indicated that the calcitriol-mediated HCV suppression was associated with the activation of VDR, interference with ERAD process, as well as blockades of PPAR, lipid accumulation and nitrative stress.