Histone deacetylase 5 (HDAC5) belongs to class II HDAC subfamily and is reported to be increased in the kidneys of diabetic patients and animals. However, little is known about its function and the exact mechanism in diabetic kidney disease (DKD). Here, we found that HDAC5 was located in renal glomeruli and tubular cells, and significantly upregulated in diabetic mice and UUO mice, especially in renal tubular cells and interstitium. Knockdown of HDAC5 ameliorated high glucose-induced epithelial–mesenchymal transition (EMT) of HK2 cells, indicated in the increased E-cadherin and decreased α-SMA, via the downregulation of TGF-β1. Furthermore, HDAC5 expression was regulated by PI3K/Akt signaling pathway and inhibition of PI3K/Akt pathway by LY294002 treatment or Akt phosphorylation mutation reduced HDAC5 and TGF-β1 expression in vitro high glucose-cultured HK2 cells. Again, high glucose stimulation downregulated total m6A RNA methylation level of HK2 cells. Then, m6A demethylase inhibitor MA2 treatment decreased Akt phosphorylation, HDAC5, and TGF-β1 expression in high glucose-cultured HK2 cells. In addition, m6A modification-associated methylase METTL3 and METTL14 were decreased by high glucose at the levels of mRNA and protein. METTL14 not METTL3 overexpression led to PI3K/Akt pathway inactivation in high glucose-treated HK2 cells by enhancing PTEN, followed by HDAC5 and TGF-β1 expression downregulation. Finally, in vivo HDACs inhibitor TSA treatment alleviated extracellular matrix accumulation in kidneys of diabetic mice, accompanied with HDAC5, TGF-β1, and α-SMA expression downregulation. These above data suggest that METTL14-regulated PI3K/Akt signaling pathway via PTEN affected HDAC5-mediated EMT of renal tubular cells in diabetic kidney disease.

Diabetic peripheral neuropathy (DPN) is the most common complication of diabetes mellitus (DM) and the dysfunction of Schwann cells plays an important role in the pathogenesis of DPN. Thioredoxin-interacting protein (TXNIP) is known as an inhibitor of thioredoxin and associated with oxidative stress and inflammation. However, whether TXNIP is involved in dysfunction of Schwann cells of DPN and the exact mechanism is still not known. In this study, we first reported that TXNIP expression was significantly increased in the sciatic nerves of diabetic mice, accompanied by abnormal electrophysiological indexes and myelin sheath structure. Similarly, in vitro cultured Schwann cells TXNIP was evidently enhanced by high glucose stimulation. Again, the function experiment found that knockdown of TXNIP in high glucose-treated RSC96 cells led to a 4.12 times increase of LC3-II/LC3-I ratio and a 25.94% decrease of cleaved caspase 3/total caspase 3 ratio. Then, DNA methyltransferase (DNMT) inhibitor 5-Aza has been reported to benefit Schwann cell in DPN, and here 5-Aza treatment reduced TXNIP protein expression, improved autophagy and inhibited apoptosis in high glucose-treated RSC96 cells and the sciatic nerves of diabetic mice. Furthermore, DNMT1 and DNMT3a upregulation were found to be involved in TXNIP overexpression in high glucose-stimulated RSC96 cells. Silencing of DNMT1 and DNMT3a effectively reversed high glucose-enhanced TXNIP. Moreover, high glucose-inhibited PI3K/Akt pathway led to DNMT1, DNMT3a, and TXNIP upregulation in RSC96 cells. Knockdown of DNMT1 and DNMT3a prevented PI3K/Akt pathway inhibition-caused TXNIP upregulation in RSC96 cells. Finally, in vivo knockout of TXNIP improved nerve conduction function, increased autophagosome and LC3 expression, and decreased cleaved Caspase 3 and Bax expression in diabetic mice. Taken together, PI3K/Akt pathway inhibition mediated high glucose-induced DNMT1 and DNMT3a overexpression, leading to cell autophagy inhibition and apoptosis via TXNIP protein upregulation in Schwann cells of DPN.

Schwann cells are the main supportive cells of the peripheral nerves. Schwann cells suffer inhibition of autophagy under hyperglycemia treatment in diabetic peripheral neuropathy (DPN). However, the exact mechanism is still not fully elucidated. We first observed the decrease of autophagy markers (LC3‐II/LC3‐I, P62) in the sciatic nerves of diabetic mice vs . normal mice, accompanied with the loss of myelinated nerve fibers and abnormal myelin sheath. In line with this, LC3‐II/LC3‐I and P62 were also significantly reduced in high glucose—treated rat Schwann cell 96 (RSC96) cells compared with normal glucose—treated cells. Furthermore, we found that trichostatin A [an inhibitor of histone deacetylase (HDAC)] evidently improved LC3‐II/LC3‐I in high glucose—treated RSC96 cells, without an effect on P62 expression. Again, HDAC1 and HDAC5 were revealed to be increased in RSC96 cells stimulated with high glucose. Inhibition of HDAC1 but not HDAC5 by small hairpin RNA vector enhanced LC3‐II/LC3‐I in high glucose—cultured RSC96 cells. In addition, LC3‐II conversion regulators [autophagy‐related protein (Atg)3, Atg5, and Atg7] were detected in high glucose—treated and HDAC1‐knockdown RSC96 cells, and Atg3 was proven to be the key target of HDAC1. The presuppression of Atg3 offset the improvement of LC3‐II/LC3‐I resulting from HDAC1 inhibition in high glucose—treated RSC96 cells. The Janus kinase (JAK)—signal transducer and activator of transcription (STAT) signaling pathway was activated in RSC96 cells treated with high glucose, which was indicated by increased STAT3 phosphorylation. Blocking STAT3 phosphorylation by chemical inhibitor AG490 induced HDAC1 down‐regulation followed by increases in Atg3 and LC3‐II/LC3‐I. Interestingly, we also found that AG490 treatment enhanced P62 expression in high glucose—stimulated RSC96 cells. Taken together, our findings demonstrate that hyperglycemia inhibits LC3‐II/LC3‐I in an HDAC1‐Atg3—dependent manner and decreases P62 expression in an HDAC‐independent manner via the JAK‐STAT3 signaling pathway in the Schwann cells of DPN.—Du, W., Wang, N., Li, F. Jia, K., An, J., Liu, Y., Wang, Y., Zhu, L., Zhao, S. Hao, J. STAT3 phosphorylation mediates high glucose—impaired cell autophagy in an HDAC1‐dependent and ‐independent manner in Schwann cells of diabetic peripheral neuropathy. FASEB J. 33, 8008–8021 (2019). www.fasebj.org

Diabetic nephropathy (DN) is a severe complication of diabetes mellitus and lipid metabolism abnormality serves a key role in the pathogenesis of DN. Sterol regulatory element‑binding protein 1 (SREBP‑1) overexpression mediates aberrant lipid accumulation in renal tubular cells of DN. However, the exact mechanism involved in increased SREBP‑1 has not been fully elucidated. The aim of the present study was to explore the mechanism involved in SREBP‑1 upregulation. Diabetic mice and high glucose‑cultured HKC cells were chosen to detect the expression of FBXW7 and SREBP‑1 using immunohistochemistry, western blotting and PCR. The present study demonstrated that F‑box and WD repeat domain containing 7 (FBXW7) expression was decreased in renal tubular cells of diabetic mice. Moreover, the co‑expression of FBXW7 and SREBP‑1 was observed in renal tubular cells, but not in the glomeruli. High glucose‑induced the downregulation of FBXW7 expression in in vitro cultured HKC cells, which was accompanied by SREBP‑1 upregulation. In addition, overexpression of FBXW7 in HKC cells led to SREBP‑1 downregulation. By contrast, knockdown of FBXW7 caused SREBP‑1 upregulation in HKC cells. It was found that the PI3K/Akt signaling pathway was activated in high glucose‑stimulated HKC cells, and inhibition of PI3K/Akt pathway using LY294002 increased FBXW7 expression and decreased SREBP‑1 expression. Taken together, the present results suggested that FBXW7 mediated high glucose‑induced SREBP‑1 expression in renal tubular cells of DN, under the regulation of the PI3K/Akt signaling pathway.