Liver-derived apolipoprotein J (ApoJ) exacerbates diabetic kidney injury by disrupting TFEB-mediated lipid homeostasis.
Background
Diabetic kidney disease (DKD), a severe complication of type 2 diabetes mellitus, is a leading cause of end-stage renal disease. Ectopic lipid accumulation in renal tubules is a key driver of lipotoxicity and DKD progression. Current treatments often fall short in fully preventing this damage. Apolipoprotein J (ApoJ), a glucose-regulated molecular chaperone, is known to influence systemic metabolic homeostasis. This study investigates ApoJ's role in DKD, specifically its impact on lipid metabolism and the mTOR-TFEB pathway, to identify novel therapeutic targets.
Study Design
Researchers first used Spearman's r analysis to assess the correlation between circulating ApoJ concentrations and renal function in a cohort of 201 individuals with type 2 diabetes mellitus. Mechanistic pathways were identified via proteomic analyses and validated using gain- and loss-of-function approaches in HK2 proximal tubular epithelial cells. Further validation involved tissue-specific ApoJ-knockout mice and additional murine models of DKD. Finally, the therapeutic potential of the ApoJ antagonist MK53 was evaluated in diabetic mice.
Results
In a cohort of 201 individuals with type 2 diabetes, circulating ApoJ concentrations were positively associated with indices of renal dysfunction, indicating a clinical link. In murine models of DKD, elevated renal ApoJ was consistently accompanied by increased lipid accumulation and significant structural kidney injury. Mechanistic studies in HK2 cells revealed that ApoJ inhibited FBW7-mediated ubiquitination of mTOR, thereby enhancing mTOR interaction with transcription factor EB (TFEB) under conditions of nutrient excess. This led to a critical lipid imbalance and subsequent renal fibrosis. > Hepatocyte-specific deletion of ApoJ effectively eliminated circulating ApoJ, prevented its detrimental accumulation in renal tubules, and significantly ameliorated diabetic kidney injury in mice. Furthermore, pharmacological blockade with the ApoJ antagonist MK53 successfully reactivated the TFEB-autophagy pathway, restored lipid homeostasis, and markedly reduced renal damage in diabetic mice.
Key Findings
- Circulating ApoJ concentrations positively correlated with renal dysfunction in 201 individuals with type 2 diabetes.
- Elevated renal ApoJ in murine DKD models linked to increased lipid accumulation and structural kidney injury.
- ApoJ inhibited
FBW7-mediatedmTORubiquitination, enhancingmTOR-TFEBinteraction, causing lipid imbalance and fibrosis. - Hepatocyte-specific
ApoJdeletion prevented renal ApoJ accumulation and ameliorated diabetic kidney injury. - Pharmacological blockade with MK53 reactivated
TFEB-autophagy, restored lipid homeostasis, and reduced renal damage in diabetic mice.
Why It Matters
These findings highlight a novel liver-to-kidney interorgan transfer mechanism for pathogenic ApoJ in diabetic kidney injury, offering a new perspective on DKD progression. Targeting ApoJ represents a promising therapeutic strategy for DKD, potentially by preventing lipid accumulation and restoring cellular homeostasis. The identification of MK53 as an ApoJ antagonist that reactivates the TFEB-autophagy pathway provides a concrete pharmacological avenue. This research suggests that future DKD protocols could involve monitoring ApoJ levels or utilizing ApoJ antagonists like MK53 to protect renal function, moving beyond current standard-of-care limitations. While preclinical, it points towards a novel class of interventions for a widespread and debilitating condition.
apolipoprotein-j
apoJ
diabetic-kidney-disease
dkd
lipid-homeostasis
mTOR