Vorapaxar treatment reduces mesangial expansion in streptozotocin-induced diabetic nephropathy in mice

PAR1-mediated Non-periodical Synchronized Calcium Oscillations in Human Mesangial Cells

Mesangial cells offer structural support to the glomerular tuft and regulate glomerular capillary flow through their contractile capabilities. These cells undergo phenotypic changes, such as proliferation and mesangial expansion, resulting in abnormal glomerular tuft formation and reduced capillary loops. Such adaptation to the changing environment is commonly associated with various glomerular diseases, including diabetic nephropathy and glomerulonephritis. Thrombin-induced mesangial remodeling was found in diabetic patients, and expression of the corresponding protease-activated receptors (PARs) in the renal mesangium was reported. However, the functional PAR-mediated signaling in mesangial cells was not examined. This study investigated protease-activated mechanisms regulating mesangial cell calcium waves that may play an essential role in the mesangial proliferation or constriction of the arteriolar cells. Our results indicate that coagulation proteases such as thrombin induce synchronized oscillations in cytoplasmic Ca2+ concentration of mesangial cells. The oscillations required PAR1 G-protein coupled receptors-related activation, but not a PAR4, and were further mediated presumably through store-operated calcium entry and transient receptor potential canonical 3 (TRPC3) channel activity. Understanding thrombin signaling pathways and their relation to mesangial cells, contractile or synthetic (proliferative) phenotype may play a role in the development of chronic kidney disease and requires further investigation.

Protease-activated receptors in kidney diseases: A comprehensive review of pathological roles, therapeutic outcomes and challenges

Studies have demonstrated that protease-activated receptors (PARs) with four subtypes (PAR1-4) are mainly expressed in the renal epithelial, endothelial, and podocyte cells. Some endogenous and urinary proteases, namely thrombin, trypsin, urokinase, and kallikrein released during diseased conditions, are responsible for activating different subtypes of PARs. Each PAR receptor subtype is involved in kidney disease of distinct aetiology. PAR1 and PAR2 have shown differential therapeutic outcomes in rodent models of type-1 and type-2 diabetic kidney diseases due to the distinct etiological basis of each disease type, however such findings need to be confirmed in other diabetic renal injury models. PAR1 and PAR2 blockers have been observed to abolish drug-induced nephrotoxicity in rodents by suppressing tubular inflammation and fibrosis and preventing mitochondrial dysfunction. Notably, PAR2 inhibition improved autophagy and prevented fibrosis, inflammation, and remodeling in the urethral obstruction model. Only the PAR1/4 subtypes have emerged as a therapeutic target for treating experimentally induced nephrotic syndrome, where their respective antibodies attenuated the podocyte apoptosis induced upon thrombin activation. Strikingly PAR2 and PAR4 subtypes involvement has been tested in sepsis-induced acute kidney injury (AKI) and renal ischemia-reperfusion injury models. Thus, more studies are required to delineate the role of other subtypes in the sepsis-AKI model. Evidence suggests that PARs regulate oxidative, inflammatory stress, immune cell activation, fibrosis, autophagic flux, and apoptosis during kidney diseases.

Natural swietenine attenuates diabetic nephropathy by regulating the NF-κB/NLRP3/Caspase-1 signaling pathways: In vivo and in vitro study

Swietenine (Swi), isolated from Swietenia macrophylla King ameliorates inflammation and oxidative stress, and diabetic nephropathy has a close connection with them. So the effects of Swi on diabetic nephropathy and its mechanism of action was explored. We divided human mesangial cells into five groups and determined the expression of NF-κB and NLRP3 inflammasomes in each group. The levels of inflammatory factors IL-1β and IL-18 were also measured. To explore the relationship between NF-κB and NLRP3, we added PDTC, a specific NF-κB inhibitor, and LPS, and divided the experimental groups into seven groups. We measured the expressions of NF-κB and NLRP3, and then added MCC950, a specific inhibitor of NLRP3 and LPS, the expression of NLRP3, Caspase-1, and IL-1β and IL-18 were measured. Animals divided into four groups and administered over 8 weeks. Protein excretion, creatinine, urea nitrogen, and uric acid were measured. Swi down regulated the expression of NF-κB, NLRP3, and Caspase-1. It reduced the levels of IL-1β and IL-18. PDTC decreased the expression of NF-κB and NLRP3. Compared with the HG + PDTC group, the expression of NF-κB and NLRP3 in the HG + Swi + PDTC group decreased significantly. After adding lipopolysaccharide, the expression of NF-κB and NLRP3 increased, but this situation was reversed after adding Swi. After adding LPS, the expression of NLRP3 and Caspase-1 increased, and the levels of IL-1β and IL-18 also increased, but this situation was reversed after the addition of Swi. Swi significantly improved the renal function of mice with diabetic nephropathy and inhibited the activation of NF-κB and the NLRP3 inflammasome and reduced inflammation by regulating the NF-κB/NLRP3/Caspase-1 signaling pathway, thereby improving diabetic nephropathy.

Lack of miRNA-17 family mediates high glucose-induced PAR-1 upregulation in glomerular mesangial cells

Upregulation of thrombin receptor protease-activated receptor 1 (PAR-1) is verified to contribute to chronic kidney diseases, including diabetic nephropathy; however, the mechanisms are still unclear. In this study, we investigated the effect of PAR-1 on high glucose-induced proliferation of human glomerular mesangial cells (HMCs), and explored the mechanism of PAR-1 upregulation from alteration of microRNAs. We found that high glucose stimulated proliferation of the mesangial cells whereas PAR-1 inhibition with vorapaxar attenuated the cell proliferation. Moreover, high glucose upregulated PAR-1 in mRNA level and protein expression while did not affect the enzymatic activity of thrombin in HMCs after 48 h culture. Then high glucose induced PAR-1 elevation was likely due to the alteration of the transcription or post-transcriptional processing. It was found that miR-17 family members including miR-17-5p, -20a-5p, and -93-5p were significantly decreased among the eight detected microRNAs only in high glucose-cultured HMCs, but miR-129-5p, miR-181a-5p, and miR-181b-5p were markedly downregulated in both high glucose-cultured HMCs and equivalent osmotic press control compared with normal glucose culture. So miR-20a was selected to confirm the role of miR-17 family on PAR-1 upregulation, finding that miR-20a-5p overexpression reversed the upregulation of PAR-1 in mRNA and protein levels induced by high glucose in HMCs. In summary, our finding indicated that PAR-1 upregulation mediated proliferation of glomerular mesangial cells induced by high glucose, and deficiency of miR-17 family resulted in PAR-1 upregulation.

Sarsasapogenin alleviates diabetic nephropathy through suppression of chronic inflammation by down-regulating PAR-1: In vivo and in vitro study

BACKGROUND

Sarsasapogenin (Sar) shows good effects on diabetic nephropathy (DN) through inhibition of the NLRP3 inflammasome, yet the potential mechanism is not well known.

PURPOSE

This study was designed to explore the regulation of thrombin and/or its receptor protease-activated receptor 1 (PAR-1) on the NLRP3 inflammasome and NF-κB signaling in DN condition, and further expounded the molecular mechanism of Sar on DN.

METHODS

Streptozotocin-induced diabetic rats were treated by gavage with Sar (0, 20 and 60 mg/kg) for consecutive 10 weeks. Then urine and serum were collected for protein excretion, creatinine, urea nitrogen, and uric acid assay reflecting renal functions, renal tissue sections for periodic acid-Schiff staining and ki67 expression reflecting cell proliferation, and renal cortex for the NLRP3 inflammasome and NF-κB signaling as well as thrombin/PAR-1 signaling. High glucose-cultured human mesangial cells (HMCs) were used to further investigate the effects and mechanisms of Sar.

RESULTS

Sar markedly ameliorated the renal functions and mesangial cell proliferation in diabetic rats, and suppressed activation of the NLRP3 inflammasome and NF-κB in renal cortex. Moreover, Sar remarkably down-regulated PAR-1 in protein and mRNA levels but didn't affect thrombin activity in kidney, although thrombin activity was significantly decreased in the renal cortex of diabetic rats. Meanwhile, high glucose induced activation of the NLRP3 inflammasome and NF-κB, and increased PAR-1 expression while didn't change thrombin activity in HMCs; however, Sar co-treatment ameliorated all the above indices. Further studies demonstrated that PAR-1 knockdown attenuated activation of the NLRP3 inflammasome and NF-κB, and Sar addition strengthened these effects in high glucose-cultured HMCs.

CONCLUSION

Sar relieved DN in rat through inhibition of the NLRP3 inflammasome and NF-κB by down-regulating PAR-1 in kidney.

Podocyte Integrin-β 3 and Activated Protein C Coordinately Restrict RhoA Signaling and Ameliorate Diabetic Nephropathy

BACKGROUND

Diabetic nephropathy (dNP), now the leading cause of ESKD, lacks efficient therapies. Coagulation protease-dependent signaling modulates dNP, in part via the G protein-coupled, protease-activated receptors (PARs). Specifically, the cytoprotective protease-activated protein C (aPC) protects from dNP, but the mechanisms are not clear.

METHODS

A combination of in vitro approaches and mouse models evaluated the role of aPC-integrin interaction and related signaling in dNP.

RESULTS

The zymogen protein C and aPC bind to podocyte integrin-β ₃, a subunit of integrin-α _v β ₃. Deficiency of this integrin impairs thrombin-mediated generation of aPC on podocytes. The interaction of aPC with integrin-α _v β ₃ induces transient binding of integrin-β ₃ with G _α13 and controls PAR-dependent RhoA signaling in podocytes. Binding of aPC to integrin-β ₃ via its RGD sequence is required for the temporal restriction of RhoA signaling in podocytes. In podocytes lacking integrin-β ₃, aPC induces sustained RhoA activation, mimicking the effect of thrombin. In vivo, overexpression of wild-type aPC suppresses pathologic renal RhoA activation and protects against dNP. Disrupting the aPC-integrin-β ₃ interaction by specifically deleting podocyte integrin-β ₃ or by abolishing aPC's integrin-binding RGD sequence enhances RhoA signaling in mice with high aPC levels and abolishes aPC's nephroprotective effect. Pharmacologic inhibition of PAR1, the pivotal thrombin receptor, restricts RhoA activation and nephroprotects RGE-aPC^high and wild-type mice.Conclusions aPC-integrin-α _v β ₃ acts as a rheostat, controlling PAR1-dependent RhoA activation in podocytes in diabetic nephropathy. These results identify integrin-α _v β ₃ as an essential coreceptor for aPC that is required for nephroprotective aPC-PAR signaling in dNP.

Thrombin activation of PAR-1 contributes to microvascular stasis in mouse models of sickle cell disease

Vaso-occlusive crisis (VOC) is the primary cause of morbidity and hospitalization in sickle cell disease (SCD); however, only 4 therapies (hydroxyurea, l-glutamine, crizanlizumab, and voxeletor) are currently approved in SCD. These agents limit the duration, severity, and frequency of crises. Activation of coagulation is a hallmark of SCD. Studies in animal models of SCD have shown that coagulation contributes to the chronic inflammation and end-organ damage associated with the disease; however, it is unknown whether coagulation directly contributes to the microvascular stasis that causes VOC. Herein, we demonstrate that inhibition of tissue factor (TF) and the downstream coagulation proteases factor Xa and thrombin significantly attenuates heme-induced microvascular stasis in mouse models of VOC. Pharmacologic inhibition of the principal thrombin receptor, protease activated receptor-1 (PAR-1), as well as deficiency of PAR-1 in all nonhematopoietic cells, also reduces stasis in sickle mice. PAR-1 deficiency was associated with reduced endothelial von Willebrand factor expression, which has been shown to mediate microvascular stasis. In addition, TF inhibition reduces lung vaso-occlusion in sickle mice mediated by arteriolar neutrophil-platelet microemboli. In sum, these results suggest that prophylactic anticoagulation might attenuate the incidence of VOC.

Dual blockade of protease-activated receptor 1 and 2 additively ameliorates diabetic kidney disease

Protease-activated receptors (PARs) are coagulation protease targets, and they increase expression of inflammatory cytokines and chemokines in various diseases. Of all PARs, previous reports have shown that PAR1 or PAR2 inhibition is protective against diabetic glomerular injury. However, how PAR1 and PAR2 cooperatively contribute to diabetic kidney disease (DKD) pathogenesis and whether dual blockade of PARs is more effective in DKD remain elusive. To address this issue, male type I diabetic Akita mice heterozygous for endothelial nitric oxide synthase were used as a model of DKD. Mice (4 mo old) were divided into four treatment groups and administered vehicle, PAR1 antagonist (E5555, 60 mg·kg^-1·day^-1), PAR2 antagonist (FSLLRY, 3 mg·kg^-1·day^-1), or E5555 + FSLLRY for 4 wk. The results showed that the urinary albumin creatinine ratio was significantly reduced when both PAR1 and PAR2 were blocked with E5555 + FSLLRY compared with the vehicle-treated group. Dual blockade of PAR1 and PAR2 by E5555 + FSLLRY additively ameliorated histological injury, including mesangial expansion, glomerular macrophage infiltration, and collagen type IV deposition. Marked reduction of inflammation- and fibrosis-related gene expression in the kidney was also observed. In vitro, PAR1 and PAR2 agonists additively increased mRNA expression of macrophage chemoattractant protein 1 or plasminogen activator inhibitor-1 in human endothelial cells. Changes induced by the PAR1 agonist were blocked by a NF-κB inhibitor, whereas those of the PAR2 agonist were blocked by MAPK and/or NF-κB inhibitors. These findings suggest that PAR1 and PAR2 additively contribute to DKD pathogenesis and that dual blockade of both could be a novel therapeutic option for treatment of patients with DKD.

Innate immunity in diabetic kidney disease

Increasing evidence suggests that renal inflammation contributes to the pathogenesis and progression of diabetic kidney disease (DKD) and that anti-inflammatory therapies might have renoprotective effects in DKD. Immune cells and resident renal cells that activate innate immunity have critical roles in triggering and sustaining inflammation in this setting. Evidence from clinical and experimental studies suggests that several innate immune pathways have potential roles in the pathogenesis and progression of DKD. Toll-like receptors detect endogenous danger-associated molecular patterns generated during diabetes and induce a sterile tubulointerstitial inflammatory response via the NF-κB signalling pathway. The NLRP3 inflammasome links sensing of metabolic stress in the diabetic kidney to activation of pro-inflammatory cascades via the induction of IL-1β and IL-18. The kallikrein-kinin system promotes inflammatory processes via the generation of bradykinins and the activation of bradykinin receptors, and activation of protease-activated receptors on kidney cells by coagulation enzymes contributes to renal inflammation and fibrosis in DKD. In addition, hyperglycaemia leads to protein glycation and activation of the complement cascade via recognition of glycated proteins by mannan-binding lectin and/or dysfunction of glycated complement regulatory proteins. Data from preclinical studies suggest that targeting these innate immune pathways could lead to novel therapies for DKD.

Pharmacological PAR-1 inhibition reduces blood glucose levels but does not improve kidney function in experimental type 2 diabetic nephropathy

Vorapaxar-dependent protease-activated receptor (PAR)-1 inhibition diminishes diabetic nephropathy in experimental type 1 diabetes. As most patients with diabetic nephropathy suffer from type 2 diabetes, the aim of this study was to investigate whether PAR-1 inhibition also limits diabetic nephropathy in experimental type 2 diabetes. Consequently, leptin-deficient black and tan brachyuric (BTBR^ob/ob) mice were randomly assigned to vorapaxar (1.75 mg/kg; twice weekly via oral gavage) or vehicle treatment, whereas matched wild-type (WT) BTBR (BTBR^WT) mice served as nondiabetic controls. Weight and (nonfasting) blood glucose levels were monitored for up to 18 wk, after which kidney function and histologic damage was evaluated postmortem. We show that blood glucose levels and body weight increased in diabetic BTBR^ob/ob mice compared with nondiabetic BTBR^WT controls. Vorapaxar-dependent PAR-1 inhibition reduced but did not normalize blood glucose levels in BTBR^ob/ob mice, whereas it potentiated the increase in body weight. Vorapaxar did not, however, preserve kidney function, whereas it only minimally reduced histopathological signs of kidney injury. Overall, we thus show that PAR-1 inhibition reduces blood glucose levels during the progression of diabetic nephropathy in experimental type 2 diabetes but does not improve renal function. This is in contrast to the therapeutic potential of vorapaxar in type 1 diabetes-induced nephropathy, highlighting the importance of disease-dependent treatment modalities.-Waasdorp, M., Florquin, S., Duitman, J., Spek, C. A. Pharmacological PAR-1 inhibition reduces blood glucose levels but does not improve kidney function in experimental type 2 diabetic nephropathy.

Role of TRPC6 in Progression of Diabetic Kidney Disease

PURPOSE OF REVIEW

The underlining goal of this review is to offer a concise, detailed look into current knowledge surrounding transient receptor potential canonical channel 6 (TRPC6) in the progression of diabetic kidney disease (DKD).

RECENT FINDINGS

Mutations and over-activation in TRPC6 channel activity lead to the development of glomeruli injury. Angiotensin II, reactive oxygen species, and other factors in the setting of DKD stimulate drastic increases in calcium influx through the TRPC6 channel, causing podocyte hypertrophy and foot process effacement. Loss of the podocytes further promote deterioration of the glomerular filtration barrier and play a major role in the development of both albuminuria and the renal injury in DKD. Recent genetic manipulation with TRPC6 channels in various rodent models provide additional knowledge about the role of TRPC6 in DKD and are reviewed here. The TRPC6 channel has a pronounced role in the progression of DKD, with deviations in activity yielding detrimental outcomes. The benefits of targeting TRPC6 or its upstream or downstream signaling pathways in DKD are prominent.