Deciphering the SUMO code in the kidney

Natural Products Against Renal Fibrosis via Modulation of SUMOylation

Renal fibrosis is the common and final pathological process of kidney diseases. As a dynamic and reversible post-translational modification, SUMOylation and deSUMOylation of transcriptional factors and key mediators significantly affect the development of renal fibrosis. Recent advances suggest that SUMOylation functions as the promising intervening target against renal fibrosis, and natural products prevent renal fibrosis via modulating SUMOylation. Here, we introduce the mechanism of SUMOylation in renal fibrosis and therapeutic effects of natural products. This process starts by summarizing the key mediators and enzymes during SUMOylation and deSUMOylation and its regulation role in transcriptional factors and key mediators in renal fibrosis, then linking the mechanism findings of SUMOylation and natural products to develop novel therapeutic candidates for treating renal fibrosis, and concludes by commenting on promising therapeutic targets and candidate natural products in renal fibrosis via modulating SUMOylation, which highlights modulating SUMOylation as a promising strategy for natural products against renal fibrosis.

Regulation of transforming growth factor-β signalling by SUMOylation and its role in fibrosis

Fibrosis is an abnormal healing process that only repairs the structure of an organ after injury and does not address damaged functions. The pathogenesis of fibrosis is multifactorial and highly complex; numerous signalling pathways are involved in this process, with the transforming growth factor-β (TGF-β) signalling pathway playing a central role. TGF-β regulates the generation of myofibroblasts and the epithelial-mesenchymal transition by regulating transcription and translation of downstream genes and precisely regulating fibrogenesis. The TGF-β signalling pathway can be modulated by various post-translational modifications, of which SUMOylation has been shown to play a key role. In this review, we focus on the function of SUMOylation in canonical and non-canonical TGF-β signalling and its role in fibrosis, providing promising therapeutic strategies for fibrosis.

SUMO1 modification of IGF-1R combining with SNAI2 inhibited osteogenic differentiation of PDLSCs stimulated by high glucose

Background

Periodontal disease, an oral disease characterized by loss of alveolar bone and progressive teeth loss, is the sixth major complication of diabetes. It is spreading worldwide as it is difficult to be cured. The insulin-like growth factor 1 receptor (IGF-1R) plays an important role in regulating functional impairment associated with diabetes. However, it is unclear whether IGF-1R expression in periodontal tissue is related to alveolar bone destruction in diabetic patients. SUMO modification has been reported in various diseases and is associated with an increasing number of biological processes, but previous studies have not focused on diabetic periodontitis. This study aimed to explore the role of IGF-1R in osteogenic differentiation of periodontal ligament stem cells (PDLSCs) in high glucose and control the multiple downstream damage signal factors.

Methods

PDLSCs were isolated and cultured after extraction of impacted teeth from healthy donors or subtractive orthodontic extraction in adolescents. PDLSCs were cultured in the osteogenic medium with different glucose concentrations prepared by medical 5% sterile glucose solution. The effects of different glucose concentrations on the osteogenic differentiation ability of PDLSCs were studied at the genetic and cellular levels by staining assay, Western Blot, RT-PCR, Co-IP and cytofluorescence.

Results

We found that SNAI2, RUNX2 expression decreased in PDLSCs cultured in high glucose osteogenic medium compared with that in normal glucose osteogenic medium, which were osteogenesis-related marker. In addition, the IGF-1R expression, sumoylation of IGF-1R and osteogenic differentiation in PDLSCs cultured in high glucose osteogenic medium were not consistent with those cultured in normal glucose osteogenic medium. However, osteogenic differentiation of PDLCSs enhanced after adding IGF-1R inhibitors to high glucose osteogenic medium.

Conclusion

Our data demonstrated that SUMO1 modification of IGF-1R inhibited osteogenic differentiation of PDLSCs by binding to SNAI2 in high glucose environment, a key factor leading to alveolar bone loss in diabetic patients. Thus we could maximize the control of multiple downstream damage signaling factors and bring new hope for alveolar bone regeneration in diabetic patients.

Krϋppel-like factor 15 suppresses renal glomerular mesangial cell proliferation via enhancing P53 SUMO1 conjugation

Mesangial cell (MC) proliferation is a key pathological feature in a number of common human renal diseases, including mesangial proliferative nephritis and diabetic nephropathies. Knowledge of MC responses to pathological stimuli is crucial to the understanding of these disease processes. We previously determined that Krϋppel‐like factor 15 (KLF15), a kidney‐enriched zinc‐finger transcription factor, was required for inhibition of MC proliferation. In the present study, we investigated the direct target gene and the underlying mechanism by which KLF15 regulated mesangial proliferation. First, we screened small ubiquitin‐related modifier 1 (SUMO1) as the direct transcriptional target of KLF15 and validated this finding with ChIP‐PCR and luciferase assays. Furthermore, we demonstrated that overexpressing KLF15 or SUMO1 enhanced the stability of P53, which blocked the cell cycle of human renal MCs (HRMCs) and therefore abolished cell proliferation. Conversely, knockdown of SUMO1 in HRMCs, even those overexpressed with KLF15, could not inhibit HRMC proliferation rates and increase SUMOylation of P53. Finally, the results showed that the levels of SUMOylated P53 in the kidney cortices of anti‐Thy 1 model rats were decreased during proliferation periods. These findings reveal the critical mechanism by which KLF15 targets SUMO1 to mediate the proliferation of MCs.

Deciphering the SUMO code in the kidney

SUMOylation of proteins is an important regulatory element in modulating protein function and has been implicated in the pathogenesis of numerous human diseases such as cancers, neurodegenerative diseases, brain injuries, diabetes, and familial dilated cardiomyopathy. Growing evidence has pointed to a significant role of SUMO in kidney diseases such as DN, RCC, nephritis, AKI, hypertonic stress and nephrolithiasis. Recently, emerging studies in podocytes demonstrated that SUMO might have a protective role against podocyte apoptosis. However, the SUMO code responsible for beneficial outcome in the kidney remains to be decrypted. Our recent experiments have revealed that the expression of both SUMO and SUMOylated proteins is appreciably elevated in hypoxia‐induced tubular epithelial cells (TECs) as well as in the unilateral ureteric obstruction (UUO) mouse model, suggesting a role of SUMO in TECs injury and renal fibrosis. In this review, we attempt to decipher the SUMO code in the development of kidney diseases by summarizing the defined function of SUMO and looking forward to the potential role of SUMO in kidney diseases, especially in the pathology of renal fibrosis and CKD, with the goal of developing strategies that maximize correct interpretation in clinical therapy and prognosis.