Protective effects of IFN-γ on the kidney of type- 2 diabetic KKAy mice

Role of SUMOylation of STAT1 in tubular epithelial‑mesenchymal transition induced by high glucose

Tubulointerstitial fibrosis (TIF) is an important pathological change that occurs during the development of diabetic kidney disease. The epithelial‑mesenchymal transition (EMT) of renal tubular epithelial cells is a manifestation of TIF. STAT1, a member of the STAT family of transcription factors, can be modified by the small ubiquitin‑related modifier (SUMO), thus affecting the activity of STAT1. The present study investigated the role of STAT1 SUMOylation in high glucose‑induced tubular EMT by western blotting, immunocytochemistry, immunofluorescence, co‑immunoprecipitation and dual luciferase reporter analysis. The results indicated that in the process of high glucose‑induced EMT, STAT1 activation protected the cells from EMT. However, high glucose also increased the SUMOylation of STAT1, which prevented STAT1 from exerting an effective protective role by inhibiting its activity.

Mitogen-activating protein kinase kinase kinase kinase-3, inhibited by Astragaloside IV through H3 lysine 4 monomethylation, promotes the progression of diabetic nephropathy by inducing apoptosis

Astragaloside IV (AS-IV) is a bioactive saponin extracted from the Astragalus root and has been reported to exert a protective effect on diabetic nephropathy (DN). However, the underlying mechanism remains unclear. Herein, we found that AS-IV treatment alleviated DN symptoms in DN mice accompanied by reduced metabolic parameters (body weight, urine microalbumin and creatinine, creatinine clearance, and serum urea nitrogen and creatinine), pathological changes, and apoptosis. Epigenetic histone modifications are closely related to diabetes and its complications, including H3 lysine 4 monomethylation (H3K4me1, a promoter of gene transcription). A ChIP-seq assay was conducted to identify the genes regulated by H3K4me1 in DN mice after AS-IV treatment and followed by a Kyoto Encyclopedia of Genes and Genomes pathway enrichment analysis. The results showed that there were 16 common genes targeted by H3K4me1 in normal and AS-IV-treated DN mice, 1148 genes were targeted by H3K4me1 only in DN mice. From the 1148 genes, we screened mitogen-activating protein kinase kinase kinase kinase-3 (MAP4K3) for the verification of gene expression and functional study. The results showed that MAP4K3 was significantly increased in DN mice and high glucose (HG)-treated NRK-52E cells, which was reversed by AS-IV. MAP4K3 silencing reduced the apoptosis of NRK-52E cells under HG condition, as evidenced by decreased cleaved caspase 3 and Bax (pro-apoptotic factors), and increased Bcl-2 and Bcl-xl (anti-apoptotic factors). Collectively, AS-IV may downregulate MAP4K3 expression by regulating H3K4me1 binding and further reducing apoptosis, which may be one of the potential mechanisms that AS-IV plays a protective effect on DN.

Role of interferons in diabetic retinopathy

Diabetic retinopathy (DR) is one of the major causes of visual impairment and irreversible blindness in developed regions. Aside from abnormal angiogenesis, inflammation is the most specific and might be the initiating factor of DR. As a key participant in inflammation, interferon-gamma (IFN-γ) can be detected in different parts of the eye and is responsible for the breakdown of the blood-retina barrier and activation of inflammatory cells and other cytokines, which accelerate neovascularization and neuroglial degeneration. In addition, IFN-γ is involved in other vascular complications of diabetes mellitus and angiogenesis-dependent diseases, such as diabetic nephropathy, cerebral microbleeds, and age-related macular degeneration. Traditional treatments, such as anti-vascular endothelial growth factor agents, vitrectomy, and laser photocoagulation therapy, are more effective for angiogenesis and not tolerable for every patient. Many ongoing clinical trials are exploring effective drugs that target inflammation. For instance, IFN-α acts against viruses and angiogenesis and is commonly used to treat malignant tumors. Moreover, IFN-α has been shown to contribute to alleviating the progression of DR and other ocular diseases. In this review, we emphasize the roles that IFNs play in the pathogenesis of DR and discuss potential clinical applications of IFNs in DR, such as diagnosis, prognosis, and therapeutic treatment.

Targeting Canonical and Non-Canonical STAT Signaling Pathways in Renal Diseases

Signal transducer and activator of transcription (STAT) plays an essential role in the inflammatory reaction and immune response of numerous renal diseases. STATs can transmit the signals of cytokines, chemokines, and growth factors from the cell membrane to the nucleus. In the canonical STAT signaling pathways, upon binding with their cognate receptors, cytokines lead to a caspase of Janus kinases (JAKs) and STATs tyrosine phosphorylation and activation. Besides receptor-associated tyrosine kinases JAKs, receptors with intrinsic tyrosine kinase activities, G-protein coupled receptors, and non-receptor tyrosine kinases can also activate STATs through tyrosine phosphorylation or, alternatively, other post-translational modifications. Activated STATs translocate into the nucleus and mediate the transcription of specific genes, thus mediating the progression of various renal diseases. Non-canonical STAT pathways consist of preassembled receptor complexes, preformed STAT dimers, unphosphorylated STATs (U-STATs), and non-canonical functions including mitochondria modulation, microtubule regulation and heterochromatin stabilization. Most studies targeting STAT signaling pathways have focused on canonical pathways, but research extending into non-canonical STAT pathways would provide novel strategies for treating renal diseases. In this review, we will introduce both canonical and non-canonical STAT pathways and their roles in a variety of renal diseases.