NR4A1 Promotes Diabetic Nephropathy by Activating Mff-Mediated Mitochondrial Fission and Suppressing Parkin-Mediated Mitophagy

Abstract

Background/Aims: Disrupted mitochondrial dynamics, including excessive mitochondrial fission and mitophagy arrest, has been identified as a pathogenic factor in diabetic nephropathy (DN), although the upstream regulatory signal for mitochondrial fission activation and mitophagy arrest in the setting of DN remains unknown. Methods: Wild-type (WT) mice and NR4A1 knockout (NR4A1-KO) mice were used to establish a DN model. Mitochondrial fission and mitophagy were evaluated by western blotting and immunofluorescence. Mitochondrial function was assessed by JC-1 staining, the mPTP opening assay, immunofluorescence and western blotting. Renal histopathology and morphometric analyses were conducted via H&E, Masson and PASM staining. Kidney function was evaluated via ELISA, western blotting and qPCR. Results: In the present study, we found that nuclear receptor subfamily 4 group A member 1 (NR4A1) was actually activated by a chronic hyperglycemic stimulus. Higher NR4A1 expression was associated with glucose metabolism disorder, renal dysfunction, kidney hypertrophy, renal fibrosis, and glomerular apoptosis. At the molecular level, increased NR4A1 expression activated p53, and the latter selectively stimulated mitochondrial fission and inhibited mitophagy by modulating Mff and Parkin transcription. Excessive Mff-related mitochondrial fission caused mitochondrial oxidative stress, promoted mPTP opening, exacerbated proapoptotic protein leakage into the cytoplasm, and finally initiated mitochondria-dependent cellular apoptosis in the setting of diabetes. In addition, defective Parkin-mediated mitophagy repressed cellular ATP production and failed to correct the uncontrolled mitochondrial fission. However, NR4A1 knockdown interrupted the Mff-related mitochondrial fission and recused Parkin-mediated mitophagy, reducing the hyperglycemia-mediated mitochondrial damage and thus improving renal function. Conclusion: Overall, we have shown that NR4A1 functions as a novel malefactor in diabetic renal damage and operates by synchronously enhancing Mff-related mitochondrial fission and repressing Parkin-mediated mitophagy. Thus, finding strategies to regulate the balance of the NR4A1-p53 signaling pathway and mitochondrial homeostasis may be a therapeutic option for treating diabetic nephropathy in clinical practice.

Interaction of Nuclear Receptor Subfamily 4 Group A Member 1 (Nr4a1) and Liver Linase B1 (LKB1) Mitigates Type 2 Diabetes Mellitus by Activating Monophosphate-Activated Protein Kinase (AMPK)/Sirtuin 1 (SIRT1) Axis and Inhibiting Nuclear Factor-kappa B (NF-κB) Activation

“…Consistently, the basal levels of Nr4a1, body weight, FBG, TG, TC, LDL-C, and HDL-C were higher in T2DM patients [30]. As recently reported, Nr4a1 was actually activated by chronic hyperglycemia, and higher Nr4a1 expression has strong links with glucose metabolism disorder, renal insufficiency, renal hypertrophy, and fibrosis, but Nr4a1 knockdown reduced diabetic renal damage [20]. Therefore, our results support that Nr4a1 depletion is beneficial for T2DM treatment.…”

“…The volume of adipocytes and the size of lipid droplets in WATs increased notably (both p<0.05, Figure 1D, 1E), inferring the successful establishment of the T2DM rat model. According to the literature, Nr4a1 is a newly-discovered malignant factor in diabetic renal damage [20]. Therefore, we speculated that Nr4a1 would have an effect on T2DM rats.…”

Sirt1 inhibits HG-induced endothelial injury: Role of Mff-based mitochondrial fission and F‑actin homeostasis-mediated cellular migration

“…Previous reports have argued that the protective endothelial effect of Sirt1 is closely associated with the regulation of mitochondrial functions by limiting mitochondrial DNA damage and preventing the activation of mitochondrial damaging MMP-9 (11,43,44). Furthermore, mitochondrial dysfunction caused by mitochondrial fission is reported to be involved in the development of diabetic nephropathy (7,45) and diabetic cardiomyopathy (46). These results indicate the involvement of mitochondrial fission in the development of HG-induced endothelial injury and diabetic vasculopathy.…”

“…Several studies have suggested that mitochondrial fission serves an important role in mitochondrial homeostasis (5,6). Furthermore, mitochondrial fission factor (Mff)-mediated mitochondrial fission is considered to be an important facet of diabetic complications (7). Excessive mitochondrial fission leads to cellular energy metabolism disorders, ROS bursts, increased mitochondrial permeability transition pore (mPTP) opening volumes and the activation of mitochondrial-dependent cell apoptotic procedures in response to HG treatment (8).…”

NIPA2 regulates osteoblast function by modulating mitophagy in type 2 diabetes osteoporosis

“…Because mitochondria are the key sites of glucose metabolism, we speculate that a precise investigation of mitophagy will shed light on the role of autophagy in type 2 diabetes osteoporosis. Sheng et al reported the positive effect of mitophagy on hyperglycemia-mediated mitochondrial damage in diabetic nephropathy 17 . In contrast, Wang et al found that attenuation of mitophagy may reduce mitochondrial loss and increase mitochondrial biogenesis in the skeletal muscles of diabetic rats 18 , but the effect of mitophagy on type 2 diabetes osteoporosis remains unclear.…”