Progress of small ubiquitin-related modifiers in kidney diseases

The causal role between circulating immune cells and diabetic nephropathy: a bidirectional Mendelian randomization with mediating insights

Diabetic nephropathy (DN) is a critical inflammatory condition linked to diabetes, affecting millions worldwide. This study employs Mendelian randomization (MR) to explore the causal relationship between immune cell signatures and DN, analyzing over 731 immune signatures and incorporating data from 1400 metabolites to investigate potential mediators. Despite no statistically significant influence of DN on immunophenotypes after FDR correction, some phenotypes with unadjusted low P-values warranted mention, including CD34 on Hematopoietic Stem Cell (Myeloid cell Panel), CD45 on CD33- HLA DR- (Myeloid cell Panel). Furthermore, three immunophenotypes were identified to have a significant impact on DN risk: CD16-CD56 on HLA DR+ NK (TBNK Panel), CD45 on HLA DR+ T cell (TBNK Panel), and CD33dim HLA DR+ CD11b+ AC (Myeloid cell Panel). Our findings underscore the critical role of immune cells in DN, highlighting potential mediators and offering new insights into its underlying mechanisms.

Ginkgolic acid promotes inflammation and macrophage apoptosis via SUMOylation and NF-κB pathways in sepsis

Background

Excessive inflammation and increased apoptosis of macrophages contribute to organ damage and poor prognosis of sepsis. Ginkgolic acid (GA) is a natural constituent extracted from the leaves of Ginkgo biloba, that can regulate inflammation and apoptosis. The present study aims to investigate the potential effect of GA in treating sepsis and its possible mechanisms.

Materials and methods

Here, a classic septic mice model and a lipopolysaccharide (LPS)-induced RAW 264.7 inflammation model were established. Cytokines in serum and culture supernatant were detected by ELISA, and the mRNA levels of them were examined by PCR. Hematoxylin and eosin (H&E) staining was performed to determine histopathological changes in liver, lung and kidney. Bacterial burden in the blood, peritoneal lavage fluids (PLFs) and organs were observed on Luria-Bertani agar medium. Flow cytometry and western blotting was used to detect apoptosis and the expression level of apoptosis related molecules, respectively. Moreover, the levels of SUMOylation were detected by western blotting. The activity of NF-κB p65 was assessed by immunofluorescence staining and western blotting.

Results

The result showed that GA promoted inflammatory responses, reduced bacterial clearance, aggravated organ damage, and increased mortality in septic mice. GA increased apoptosis in peritoneal macrophages (PMs) and RAW 264.7 cells. Meanwhile, GA inhibited SUMOylation and increased the nuclear translocation of NF-κB p65 as well as its phosphorylation level.

Conclusion

Collectively, GA promotes inflammation and macrophage apoptosis in sepsis, which may be mediated by inhibiting the SUMOylation process and increasing NF-κB p65 activity.

Poricoic Acid A Inhibits the NF-κB/MAPK Pathway to Alleviate Renal Fibrosis in Rats with Cardiorenal Syndrome

Objective

To explore the potential and mechanism of action of poricoic acid A (PAA) in treatment of cardiorenal injury and fibrosis due to cardiorenal syndrome (CRS).

Materials and Methods

A CRS rat model was established by transabdominal subtotal nephrectomy (STNx). The experimental group was treated by gavage of PAA (10 mg/kg/day). After 8 weeks of treatment, echocardiography was utilized for detecting heart-related indexes in rats. HE and Masson staining were conducted to detect the degree of pathological damage and fibrosis in rat kidney tissue, respectively. In addition, serum blood urea nitrogen (BUN), serum creatinine (SCr), and 24-hour urine protein were measured biochemically. Also, the levels of inflammatory factors (IL-1β, IL-6, and IL-10) in rat kidneys were measured using ELISA. Western blot was used to examine the expression of NF-κB/MAPK pathway-related proteins.

Results

In this study, a CRS rat model was successfully established by STNx surgery. PAA treatment could significantly alleviate the damage of heart and kidney function in CRS rats and reduce the pathological damage of kidney tissue and renal fibrosis. Meanwhile, PAA could also inhibit the renal inflammatory response through downregulating IL-1β and IL-6 levels in the kidney tissue and upregulating IL-10 level. Further mechanism exploration showed that the NF-κB/MAPK signaling pathway was significantly activated in CRS rats, while PAA treatment could markedly inhibit the NF-κB/MAPK signaling pathway activity in CRS rats.

Conclusion

PAA can obviously improve the pathological damage and fibrosis of renal tissue in CRS rats and maintain the function of the heart and kidney. The above functions of PAA may be achieved by inhibiting the NF-κB/MAPK signaling pathway activity. Briefly speaking, PAA can serve as a potential drug for CRS treatment.

Ginkgolic acid improves bleomycin-induced pulmonary fibrosis by inhibiting SMAD4 SUMOylation

Idiopathic pulmonary fibrosis (IPF) is a refractory chronic respiratory disease with progressively exacerbating symptoms and a high mortality rate. There are currently only two effective drugs for IPF; thus, there is an urgent need to develop new therapeutics. Previous experiments have shown that ginkgolic acid (GA), as a SUMO-1 inhibitor, exerted an inhibitory effect on cardiac fibrosis induced by myocardial infarction. Regarding the pathogenesis of PF, previous studies have concluded that small ubiquitin-like modifier (SUMO) polypeptides bind multiple target proteins and participate in fibrosis of multiple organs, including PF. In this study, we found altered expression of SUMO family members in lung tissues from IPF patients. GA mediated the reduced expression of SUMO1/2/3 and the overexpression of SENP1 in a PF mouse model, which improved PF phenotypes. At the same time, the protective effect of GA on PF was also confirmed in the SENP1-KO transgenic mice model. Subsequent experiments showed that SUMOylation of SMAD4 was involved in PF. It was inhibited by TGF-β1, but GA could reverse the effects of TGF-β1. SENP1 also inhibited the SUMOylation of SMAD4 and then participated in epithelial-mesenchymal transition (EMT) downstream of TGF-β1. We also found that SENP1 regulation of SMAD4 SUMOylation affected reactive oxygen species (ROS) production during TGF-β1-induced EMT and that GA prevented this oxidative stress through SENP1. Therefore, GA may inhibit the SUMOylation of SMAD4 through SENP1 and participate in TGF-β1-mediated pulmonary EMT, all of which reduce the degree of PF. This study provided potential novel targets and a new alternative for the future clinical testing in PF.

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.

The Hydrogen-Coupled Oligopeptide Membrane Cotransporter Pept2 is SUMOylated in Kidney Distal Convoluted Tubule Cells

Protein post-translational modification by the Small Ubiquitin-like MOdifier (SUMO) on lysine residues is a reversible process highly important for transcription and protein stability. In the kidney, SUMOylation appears to be important for the cellular response to aldosterone. Therefore, in this study, we generated a SUMOylation profile of the aldosterone-sensitive kidney distal convoluted tubule (DCT) as a basis for understanding SUMOylation events in this cell type. Using mass spectrometry-based proteomics, 1037 SUMO1 and 552 SUMO2 sites, corresponding to 546 SUMO1 and 356 SUMO2 proteins, were identified from a modified mouse kidney DCT cell line (mpkDCT). SUMOylation of the renal hydrogen-coupled oligopeptide and drug co-transporter (Pept2) at one site (K139) was found to be highly regulated by aldosterone. Using immunolabelling of mouse kidney sections Pept2 was localized to DCT cells in vivo. Aldosterone stimulation of mpkDCT cell lines expressing wild-type Pept2 or mutant K139R-Pept2, post-transcriptionally increased Pept2 expression up to four-fold. Aldosterone decreased wild-type Pept2 abundance in the apical membrane domain of mpkDCT cells, but this response was absent in K139R-Pept2 expressing cells. In summary, we have generated a SUMOylation landscape of the mouse DCT and determined that SUMOylation plays an important role in the physiological regulation of Pept2 trafficking by aldosterone.

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.

SENP1 modulates microglia-mediated neuroinflammation toward intermittent hypoxia-induced cognitive decline through the de-SUMOylation of NEMO

Intermittent hypoxia (IH)‐induced cognition decline is related to the neuroinflammation in microglia. SUMOylation is associated with multiple human diseases, which can be reversed by sentrin/SUMO‐specific proteases 1 (SENP1). Herein, we investigated the role of SENP1 in IH‐induced inflammation and cognition decline. BV‐2 microglial cells and mice were used for inflammatory response and cognition function evaluation following IH treatment. Biochemical analysis and Morris water maze methods were used to elaborate the mechanism of SENP1 in IH impairment. Molecular results revealed that IH induced the inflammatory response, as evidenced by the up‐regulation of NF‐κB activation, IL‐1β and TNF‐α in vitro and in vivo. Moreover, IH decreased the expression of SENP1, and increased the SUMOylation of NEMO, not NF‐κB P65. Moreover, SENP1 overexpression inhibited IH‐induced inflammatory response and SUMOylation of NEMO. However, the inhibitions were abolished by siRNA‐NEMO. In contrast, SENP1 depletion enhanced IH‐induced inflammatory response and SUMOylation of NEMO, accompanying with increased latency and reduced dwell time in mice. Overall, the results demonstrated that SENP1 regulated IH‐induced neuroinflammation by modulating the SUMOylation of NEMO, thus activating the NF‐κB pathway, revealing that targeting SENP1 in microglia may represent a novel therapeutic strategy for IH‐induced cognitive decline.

The complex interplay between kidney injury and inflammation

Acute kidney injury (AKI) has gained significant attention following patient safety alerts about the increased risk of harm to patients, including increased mortality and hospitalization. Common causes of AKI include hypovolaemia, nephrotoxic medications, ischaemia and acute glomerulonephritis, although in reality it may be undetermined or multifactorial. A period of inflammation either as a contributor to the kidney injury or resulting from the injury is almost universally seen. This article was compiled following a workshop exploring the interplay between injury and inflammation. AKI is characterized by some degree of renal cell death through either apoptosis or necrosis, together with a strong inflammatory response. Studies interrogating the resolution of renal inflammation identify a whole range of molecules that are upregulated and confirm that the kidneys are able to intrinsically regenerate after an episode of AKI, provided the threshold of damage is not too high. Kidneys are unable to generate new nephrons, and dysfunctional or repeated episodes will lead to further nephron loss that is ultimately associated with the development of renal fibrosis and chronic kidney disease (CKD). The AKI to CKD transition is a complex process mainly facilitated by maladaptive repair mechanisms. Early biomarkers mapping out this process would allow a personalized approach to identifying patients with AKI who are at high risk of developing fibrosis and subsequent CKD. This review article highlights this process and explains how laboratory models of renal inflammation and injury assist with understanding the underlying disease process and allow interrogation of medications aimed at targeting the mechanistic interplay.

Poricoic acid A suppresses TGF-β1-induced renal fibrosis and proliferation via the PDGF-C, Smad3 and MAPK pathways

Renal interstitial fibrosis is the most important pathological process in chronic renal failure. Previous studies have shown that poricoic acid A (PAA), the main chemical constituent on the surface layer of the mushroom Poria cocos, has protective effects against oxidative stress and acute kidney injury. The present study aimed to investigate the potential roles of PAA on the pathological process of renal fibrosis and the associated molecular mechanism. The NRK-49F cell line was treated with transforming growth factor-β1 (TGF-β1) with or without PAA or platelet-derived growth factor C (PDGF-C). Cell Counting Kit-8 assay, western blotting and 5-ethynyl-2'-deoxyuridine immunofluorescence staining were performed to examine cell growth, protein expression and cell proliferation, respectively. Data from the present study showed that 10 µM PAA attenuated TGF-β1-induced NRK-49F cell extracellular matrix (ECM) accumulation, fibrosis formation and proliferation. Renal fibrosis with the activation of Smad3 and mitogen-activated protein kinase (MAPK) pathways were also inhibited by PAA treatment. PDGF-C reversed the inhibitory effects of PAA on TGF-β1-induced renal fibroblast proliferation and activation of the Smad3/MAPK pathway. The present study suggested that suppression of TGF-β1-induced renal fibroblast ECM accumulation, fibrosis formation and proliferation by PAA is mediated via the inhibition of the PDGF-C, Smad3 and MAPK pathways. The present findings not only revealed the potential anti-fibrotic effects of PAA on renal fibroblasts, but also provided a new insight into the prevention of fibrosis formation via regulation of the PDGF-C, Smad3 and MAPK signaling pathways.

Protection against acute renal injury by naturally occurring medicines which act through Nrf2 signaling pathway

The cellular defense pathway plays a key role in maintaining the homeostasis, tissues and organisms. Nuclear factor E2-related factor 2 (Nrf2), as a key cell signaling pathway, plays an important role in encoding detoxification enzymes and other stress response mediators. Recent studies have shown that it is closely related to the prevention and treatment of acute kidney injury (AKI). Therefore, this article reviews the protective effects of Nrf2-related signaling pathways on acute kidney injury, and summarizes the strategies of natural pharmaceutical ingredients such as flavonoids, alkaloids, terpenes, phenylpropionic acid, polyphenols, and polysaccharides to prevent and treat acute kidney injury. It is of great significance to further study the relationship between Nrf2 regulated signal pathway and kidney disease and the development of new medicines for acute kidney injury treatment. It can also provide new ideas and treatment strategies for clinical treatment of acute kidney injury. PRACTICAL APPLICATIONS: This article reviewed the mechanisms by which the active ingredients of natural medicines slow down acute kidney injury through the Nrf2 pathway. It will help us to understand the regulatory role of the Nrf2 pathway in AKI more comprehensively, and provide a theoretical basis for further exploring the mechanism of more natural drugs to reduce acute kidney injury.

SUMOylation Landscape of Renal Cortical Collecting Duct Cells

Protein post-translational modification by the small ubiquitin-like modifier (SUMO) is a mechanism that allows a diverse response of cells to stress. Five SUMO family members, SUMO1-5, are expressed in mammals. We hypothesized that because kidney epithelial cells are often subject to stresses arising from various physiological conditions, multiple proteins in the kidney will be SUMOylated. Here, we profiled SUMO1- and SUMO2-modified proteins in a polarized epithelial cell model of the renal cortical collecting duct (mpkCCD14 cells). Modified forms of SUMO1 or SUMO2, with a histidine tag and a Thr to Lys mutation preceding the carboxyl-terminal di-gly motif, were expressed in mpkCCD14 cells, allowing SUMO-conjugated proteins to be purified and identified. Protein mass spectrometry identified 1428 SUMO1 and 1957 SUMO2 sites, corresponding to 741 SUMO1 and 971 SUMO2 proteins. Gene ontology indicated that the function of the majority of SUMOylated proteins in mpkCCD14 cells was related to gene transcription. After treatment of the mpkCCD14 cells for 24 h with aldosterone, the levels of SUMOylation at a specific site on the proton and oligopeptide/antibiotic cotransporter protein Pept2 were greatly increased. In conclusion, the SUMOylation landscape of mpkCCD14 cells suggests that protein modification by SUMOylation is a mechanism within renal epithelial cells to modulate gene transcription under various physiological conditions.