The role of hypoxia-inducible factors in renal fibrosis

Chronic constant light exposure aggravates high fat diet-induced renal injury in rats

Obesity-related kidney disease is now recognized as a global health issue, with a substantial number of patients developing progressive renal failure and end-stage renal disease. Interestingly, recent studies indicate light pollution is a novel environmental risk factor for chronic kidney disease. However, the impact of light pollution on obesity-related kidney disease remains largely unknown, with its underlying mechanism insufficiently explained. Renal hypoxia induced factor 1α (HIF1α) is critical in the development of glomerulosclerosis and renal fibrosis. The present study explored effects of constant light exposure on high fat diet (HFD) -induced renal injury and its association with HIF1α signal pathway. Thirty-two male Sprague Dawley rats were divided into four groups according to diet (HFD or normal chow diet) and light cycles (light/dark or constant light). After 16 weeks treatment, rats were sacrificed and pathophysiological assessments were performed. In normal chow fed rats, constant light exposure led to glucose abnormalities and dyslipidemia. In HFD fed rats, constant light exposure exacerbated obesity, glucose abnormalities, insulin resistance, dyslipidemia, renal functional decline, proteinuria, glomerulomegaly, renal inflammation and fibrosis. And, constant light exposure caused an increase in HIF1α and a decrease in prolyl hydroxylase domain 1 (PHD1) and PHD2 expression in kidneys of HFD-fed rats. Then, we demonstrated that BMAL1 bound directly to the promoters of PHD1 in mouse podocyte clone 5 cell line (MPC5) by ChIP assays. In conclusion, chronic constant light exposure aggravates HFD-induced renal injuries in rats, and it is associated with activation of HIF1α signal pathway.

Study of the Active Components and Molecular Mechanism of Tripterygium wilfordii in the Treatment of Diabetic Nephropathy

We aimed to explore the active ingredients and molecular mechanism of Tripterygium wilfordii (TW) in the treatment of diabetic nephropathy (DN) through network pharmacology and molecular biology. First, the active ingredients and potential targets of TW were obtained through the Traditional Chinese Medicine Systems Pharmacology Database and Analysis Platform (TCMSP) and related literature materials, and Cytoscape 3.7.2 software was used to construct the active ingredient-target network diagram of TW. Second, the target set of DN was obtained through the disease database, and the potential targets of TW in the treatment of DN were screened through a Venn diagram. A protein interaction network diagram (PPI) was constructed with the help of the String platform and Cytoscape 3.7.2. Third, the ClueGO plug-in tool was used to enrich the GO biological process and the KEGG metabolic pathway. Finally, molecular docking experiments and cell pathway analyses were performed. As a result, a total of 52 active ingredients of TW were screened, and 141 predicted targets and 49 target genes related to DN were identified. The biological process of GO is mediated mainly through the regulation of oxygen metabolism, endothelial cell proliferation, acute inflammation, apoptotic signal transduction pathway, fibroblast proliferation, positive regulation of cyclase activity, adipocyte differentiation and other biological processes. KEGG enrichment analysis showed that the main pathways involved were AGE-RAGE, vascular endothelial growth factor, HIF-1, IL-17, relaxin signalling pathway, TNF, Fc epsilon RI, insulin resistance and other signaling pathways. It can be concluded that TW may treat DN by reducing inflammation, reducing antioxidative stress, regulating immunity, improving vascular disease, reducing insulin resistance, delaying renal fibrosis, repairing podocytes, and reducing cell apoptosis, among others, with multicomponent, multitarget and multisystem characteristics.

The Effects of Chronic Intermittent Hypoxia in Bleomycin-Induced Lung Injury on Pulmonary Fibrosis via Regulating the NF-κB/Nrf2 Signaling Pathway

Background

Obstructive sleep apnea (OSA) is associated with pulmonary fibrosis. Chronic intermittent hypoxia (CIH) is considered to be a surrogate of OSA. However, its exact role in pulmonary fibrosis remains uncertain. Therefore, we investigated the mechanism underlying CIH-induced pulmonary fibrosis and the role of the anti-fibrotic agent in bleomycin (BLE) induced lung injury.

Methods

Mice were divided into eight groups: the normoxia (NOR), CIH, NOR plus BLE, CIH plus BLE, NOR plus pirfenidone (PF), CIH plus PF, NOR plus BLE and PF, and CIH plus BLE and PF groups. BLE was administered intratracheally on day 14 following CIH or NOR exposure. Subsequently, the mice were exposed to CIH or NOR for an additional 4 weeks. PF was administered orally on day 5 after BLE instillation once daily for 3 weeks.

Results

In the BLE-treated groups, CIH-induced more collagen deposition in lung tissues than NOR, and significantly increased hydroxyproline and transforming growth factor-β expression. The CIH and BLE-treated groups showed increased lung inflammation compared to NOR or CIH groups. Following CIH with BLE treatment, nuclear factor-κB (NF-κB) protein expression was significantly increased, whereas nuclear factor-erythroid-related factor 2 (Nrf2) and heme oxygenase-1 protein levels were decreased. After PF treatment, NF-κB and Kelch-like ECH-associated protein 1 expression were suppressed, and Nrf2 expression was increased.

Conclusion

CIH accelerated lung fibrosis in BLE-induced lung injury in mice, potentially by regulating the NF-κB/Nrf2 signaling pathway. Our results implicate PF as a potential therapeutic agent for treating pulmonary fibrosis in individuals with OSA and idiopathic pulmonary fibrosis.

Effect and Regulation of the NLRP3 Inflammasome During Renal Fibrosis

Renal fibrosis is a common pathological process where certain primary or secondary kidney diseases can continue to progress to the end-stage of the kidney disease; however, the molecular mechanisms underlying renal fibrosis remain unclear. Recently, research focusing on examining the function of inflammasomes has attracted a great deal of attention, and data derived from these research projects have increased our understanding of the effects and regulation of inflammasomes during renal fibrosis. Based on this, the present review summarizes recent findings in regard to NLRP3 inflammasome functions during various kidney diseases, and these findings indicate that the NLRP3 inflammasome not only mediates the inflammatory response but is also associated with pyroptosis, mitochondrial regulation, and myofibroblast differentiation during renal fibrosis. These novel findings provide us with a more in-depth understanding of the pathogenesis of renal fibrosis and will aid in the identification of new targets that can be used for the prevention and treatment of this disease.

Based on HIF-1α/Wnt/β-Catenin Pathway to Explore the Effect of Qingshen Granules on Chronic Renal Failure Patients: A Randomized Controlled Trial

Objectives. This study investigates the effect of Qingshen Granules (QSG) on chronic renal failure patients and the HIF-1α/Wnt/β-catenin signaling pathway. Methods. Subjects were randomly divided into treatment and control groups, with 42 patients in each group. Participants in the treatment group received 10 g oral doses of QSG 3 times a day, for 12 weeks, whereas subjects in the control group were given a placebo. The effective rates of traditional Chinese medicine (TCM) symptom, serum creatinine (Scr), and estimate glomerular filtration rate (eGFR) as well as the serum levels of HIF-1α, Wnt1, β-catenin, α-SMA, and E-cadherin were evaluated. Results. Eighty patients completed the treatment program and two dropped out. After 12 weeks, the effective rates of TCM symptom and eGFR were found to be higher in the treatment group than in the control group, with statistically significant differences (P = 0.024 and 0.019, respectively). Meanwhile, lower levels of HIF-1α, Wnt1, β-catenin, α-SMA, and E-cadherin were detected in the treatment group, and the differences were statistically significant (P ≤ 0.001, P = 0.001, P ≤ 0.001, P ≤ 0.001, and P = 0.039). No adverse events occurred during the study. Conclusions. QSG can alleviate the clinical symptoms of chronic renal failure (CRF) and protect renal function in patients by influencing the HIF-1α/Wnt/β-catenin signaling pathway. The treatment exhibits no adverse effects and is thus safe to be used by humans.

Chronic intermittent hypoxia worsens bleomycin-induced lung fibrosis in rats

Obstructive sleep apnea (OSA) has been linked to increased mortality in pulmonary fibrosis. Its key feature, chronic intermittent hypoxia (CIH), can lead to oxidative stress and inflammation, known to lead to fibrotic pathology in other organs. We tested the effects of CIH in an animal model of bleomycin-induced lung fibrosis. Sprague Dawley rats were instilled intratracheally with bleomycin (Blm) or saline (Sal), and exposed to CIH or normal air (Norm) for 9 or 30 days. Pulmonary function was tested and lungs were harvested for histological and molecular analyses. In Blm-treated animals, 30days of CIH compared to Norm increased total lung collagen content (p=0.008) and reduced Quasi-static lung compliance (p=0.04). CIH upregulated lipid peroxidation and increased NF-κB activation, IL-17 mRNA and Col1α1 mRNA expression. Our results indicate that following Blm-induced lung injury, CIH amplifies collagen deposition via oxidative and inflammatory pathways, culminating in stiffer lungs. Thus, OSA may augment fibrosis in patients with interstitial lung disease.

Sphingosine-1-phosphate pathway in renal fibrosis

Renal fibrosis is defined as the excessive deposition and modification of extracellular matrix (ECM) in the renal parenchyma in response to injury and inflammation, resulting in renal function loss. This condition is common to many chronic kidney diseases occurring under diverse pathological conditions, such as diabetic and hypertensive nephropathy. Sphingosine-1-phosphate (S1P) is a bioactive sphingolipid metabolite involved in the regulation of cardiovascular functions and the pathogenesis of various cardiovascular diseases. S1P has also been considered an important regulator of fibrotic diseases, playing significant roles in the differentiation of fibroblasts to myofibroblasts and in the induction of inflammatory responses during the early stages of fibrotic diseases. This minireview summarizes recent research findings regarding the importance of the sphingosine kinase-1-S1P-S1P receptor axis and its interactions with other classic fibrotic signaling pathways and the immune inflammatory response to reveal novel therapeutic targets for the treatment or prevention of renal fibrosis.

Microvascular pericytes in healthy and diseased kidneys

Pericytes are interstitial mesenchymal cells found in many major organs. In the kidney, microvascular pericytes are defined anatomically as extensively branched, collagen-producing cells in close contact with endothelial cells. Although many molecular markers have been proposed, none of them can identify the pericytes with satisfactory specificity or sensitivity. The roles of microvascular pericytes in kidneys were poorly understood in the past. Recently, by using genetic lineage tracing to label collagen-producing cells or mesenchymal cells, the elusive characteristics of the pericytes have been illuminated. The purpose of this article is to review recent advances in the understanding of microvascular pericytes in the kidneys. In healthy kidney, the pericytes are found to take part in the maintenance of microvascular stability. Detachment of the pericytes from the microvasculature and loss of the close contact with endothelial cells have been observed during renal insult. Renal microvascular pericytes have been shown to be the major source of scar-forming myofibroblasts in fibrogenic kidney disease. Targeting the crosstalk between pericytes and neighboring endothelial cells or tubular epithelial cells may inhibit the pericyte-myofibroblast transition, prevent peritubular capillary rarefaction, and attenuate renal fibrosis. In addition, renal pericytes deserve attention for their potential to produce erythropoietin in healthy kidneys as pericytes stand in the front line, sensing the change of oxygenation and hemoglobin concentration. Further delineation of the mechanisms underlying the reduced erythropoietin production occurring during pericyte-myofibroblast transition may be promising for the development of new treatment strategies for anemia in chronic kidney disease.