Roles of the Skp2/p27 axis in the progression of chronic nephropathy

Upregulated SKP2 Empowers Epidermal Proliferation Through Downregulation of P27 Kip1

BACKGROUND

Excessive growth of keratinocytes is the critical event in the etiology of psoriasis. However, the underlying molecular mechanism of psoriatic keratinocyte hyperproliferation is still unclear.

OBJECTIVE

This study aimed to figure out the potential contributory role of S-phase kinase-associated protein 2 (SKP2) in promoting the hyperproliferation of keratinocytes in psoriasis.

METHODS

We analyzed microarray data (GSE41662) to investigate the gene expression of SKP2 in psoriatic lesion skins compared with their adjacent non-lesional skin. Then, we further confirmed the mRNA and protein expression of SKP2 in human psoriatic skin tissues, imiquimod (IMQ)-induced psoriatic mice back skins and tumor necrosis factor α (TNF-α), interleukin (IL)-17A and IL-6-stimulated keratinocytes by using real-time quantitative polymerase chain reaction and western blot (WB). Furthermore, we explored the potential pathogenic role and its underlying cellular mechanism of SKP2 in promoting keratinocytes hyperproliferation through 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay, cell cycle detection, 5-ethynyl-2'-deoxyuridine staining and WB. Finally, we determined whether inhibition of SKP2 can effectively alleviate the keratinocytes hyperproliferation in vivo.

RESULTS

We identified that SKP2 is aberrantly upregulated in the psoriatic lesion skin and cytokines-stimulated keratinocytes. Moreover, upregulated SKP2 augments cytokines-induced keratinocytes hyperproliferation. Mechanistically, enhanced SKP2 increased the S phase ratio through inhibiting Cyclin-Dependent Kinase Inhibitor p27 (P27 Kip1) expression. Correspondingly, suppression of SKP2 with SMIP004 can significantly ease the epidermis hyperplasia in vivo.

CONCLUSION

Our results suggest that elevated SKP2 can empower keratinocytes proliferation and psoriasis-like epidermis hyperplasia via downregulation of P27 Kip1. Therefore, targeting SKP2-P27 Kip1 axis might be a promising therapeutic strategy for the treatment of psoriasis in future.

CBGA ameliorates inflammation and fibrosis in nephropathy

Cannabidiol (CBD) is thought to have multiple biological effects, including the ability to attenuate inflammatory processes. Cannabigerols (CBGA and its decarboxylated CBG molecule) have pharmacological profiles similar to CBD. The endocannabinoid system has recently emerged to contribute to kidney disease, however, the therapeutic properties of cannabinoids in kidney disease remain largely unknown. In this study, we determined whether CBD and CBGA can attenuate kidney damage in an acute kidney disease model induced by the chemotherapeutic cisplatin. In addition, we evaluated the anti-fibrosis effects of these cannabinoids in a chronic kidney disease model induced by unilateral ureteral obstruction (UUO). We find that CBGA, but not CBD, protects the kidney from cisplatin-induced nephrotoxicity. CBGA also strongly suppressed mRNA of inflammatory cytokines in cisplatin-induced nephropathy, whereas CBD treatment was only partially effective. Furthermore, both CBGA and CBD treatment significantly reduced apoptosis through inhibition of caspase-3 activity. In UUO kidneys, both CBGA and CBD strongly reduced renal fibrosis. Finally, we find that CBGA, but not CBD, has a potent inhibitory effect on the channel-kinase TRPM7. We conclude that CBGA and CBD possess reno-protective properties, with CBGA having a higher efficacy, likely due to its dual anti-inflammatory and anti-fibrotic effects paired with TRPM7 inhibition.

Insights into the aberrant CDK4/6 signaling pathway as a therapeutic target in tumorigenesis

The recent findings advance our knowledge for the prevention of the premature activation of the major oncogenic pathways including MYC and the cyclin D-cyclin-dependent kinases 4 and 6 (CDK4/6) axis. D-type cyclins are frequently deregulated in human cancer and promote cell division in part through activation of CDK4/6. Therefore, the activation of the cyclin D-CDK4/6 axis stimulates cell proliferation and cancer progression, which represents a unique therapeutic target. However, we have shown that inhibition of CDK4/6 upregulates protein levels of RB1 and CDK6 for acquisition of drug resistance to CDK4/6 inhibitors. Here, we review new progress in the control of cyclin D-dependent cancer cell cycle and proliferation, along with identification of novel E3 ligase for the stability of cyclin D. Cullin4-RING E3 ligase (CRL4)AMBRA1 complex plays a critical role in regulating D-type cyclins through their protein destabilization to control S phase entry and maintain genomic integrity. We also summarize the strategy for inhibition of the cyclin D-associated kinases CDK4/6 and other potential cell cycle regulators for targeting cancer with altered cyclin D expression. We also uncover the function of CK1ɛ as an effective target to potentiate therapeutic efficacy of CDK4/6 inhibitors. Moreover, as the level of PD-L1 is considered in the severe clinical problem in the patients treated with CDK4 inhibitors, we assume that a therapeutic combination using PD-L1 immunotherapy might lower the development of drug resistance and targeting cyclin D will likely inhibit tumor growth and overcome resistance to cyclin D-associated CDK4/6 inhibitors.

Molecular Pathogenesis of Pulmonary Fibrosis, with Focus on Pathways Related to TGF-β and the Ubiquitin-Proteasome Pathway

Idiopathic pulmonary fibrosis (IPF) is a progressive and fatal interstitial lung disease. During the past decade, novel pathogenic mechanisms of IPF have been elucidated that have shifted the concept of IPF from an inflammatory-driven to an epithelial-driven disease. Dysregulated repair responses induced by recurrent epithelial cell damage and excessive extracellular matrix accumulation result in pulmonary fibrosis. Although there is currently no curative therapy for IPF, two medications, pirfenidone and nintedanib, have been introduced based on understanding the pathogenesis of the disease. In this review, we discuss advances in understanding IPF pathogenesis, highlighting epithelial-mesenchymal transition (EMT), the ubiquitin-proteasome system, and endothelial cells. TGF-β is a central regulator involved in EMT and pulmonary fibrosis. HECT-, RING finger-, and U-box-type E3 ubiquitin ligases regulate TGF-β-Smad pathway-mediated EMT via the ubiquitin-proteasome pathway. p27 degradation mediated by the SCF-type E3 ligase, Skp2, contributes to the progression of pulmonary fibrosis by promotion of either mesenchymal fibroblast proliferation, EMT, or both. In addition to fibroblasts as key effector cells in myofibroblast differentiation and extracellular matrix deposition, endothelial cells also play a role in the processes of IPF. Endothelial cells can transform into myofibroblasts; therefore, endothelial-mesenchymal transition can be another source of myofibroblasts.

TRPM7 contributes to progressive nephropathy

TRPM7 belongs to the Transient Receptor Potential Melastatin family of ion channels and is a divalent cation-conducting ion channel fused with a functional kinase. TRPM7 plays a key role in a variety of diseases, including neuronal death in ischemia, cancer, cardiac atrial fibrillation, malaria invasion. TRPM7 is aberrantly over-expressed in lung, liver and heart fibrosis. It is also overexpressed after renal ischemia-reperfusion, an event that induces kidney injury and fibrosis. However, the role of TRPM7 in kidney fibrosis is unclear. Using the unilateral ureteral obstruction (UUO) mouse model, we examined whether TRPM7 contributes to progressive renal damage and fibrosis. We find that TRPM7 expression increases in UUO kidneys. Systemic application of NS8593, a known TRPM7 inhibitor, prevents kidney atrophy in UUO kidneys, retains tubular formation, and reduces TRPM7 expression to normal levels. Cell proliferation of both tubular epithelial cells and interstitial cells is reduced by NS8593 treatment in UUO kidneys, as are TGF-β1/Smad signaling events. We conclude that TRPM7 is upregulated during inflammatory renal damage and propose that pharmacological intervention targeting TRPM7 may prove protective in progressive kidney fibrosis.

Inhibiting Skp2 E3 Ligase Suppresses Bleomycin-Induced Pulmonary Fibrosis

Idiopathic pulmonary fibrosis (IPF) is a progressive disease with poor prognosis and no curative therapies. SCF-Skp2 E3 ligase is a target for cancer therapy, but there have been no reports about Skp2 as a target for IPF. Here we demonstrate that Skp2 is a promising therapeutic target for IPF. We examined whether disrupting Skp2 suppressed pulmonary fibrosis in a bleomycin (BLM)-induced mouse model and found that pulmonary fibrosis was significantly suppressed in Skp2-deficient mice compared with controls. The pulmonary accumulation of fibrotic markers such as collagen type 1 and fibronectin in BLM-infused mice was decreased in Skp2-deficient mice. Moreover, the number of bronchoalveolar lavage fluid cells accompanied with pulmonary fibrosis was significantly diminished. Levels of the Skp2 target p27 were significantly decreased by BLM-administration in wild-type mice, but recovered in Skp2^-/- mice. In vimentin-positive mesenchymal fibroblasts, the decrease of p27-positive cells and increase of Ki67-positive cells by BLM-administration was suppressed by Skp2-deficency. As these results suggested that inhibiting Skp2 might be effective for BLM-induced pulmonary fibrosis, we next performed a treatment experiment using the Skp2 inhibitor SZL-P1-41. As expected, BLM-induced pulmonary fibrosis was significantly inhibited by SZL-P1-41. Moreover, p27 levels were increased by the SZL-P1-41 treatment, suggesting p27 may be an important Skp2 target for BLM-induced pulmonary fibrosis. Our study suggests that Skp2 is a potential molecular target for human pulmonary fibrosis including IPF.

Pressure and stretch differentially affect proliferation of renal proximal tubular cells

Renal obstruction is frequently found in adults and children. Mechanical stimuli, including pressure and stretch in the obstructed kidney, contribute to damage; animal models of obstruction are characterized by increased cellular proliferation. We were interested in the direct effects of pressure and stretch on renal tubular cell proliferation. Human HKC-8 or rat NRK-52E proximal tubule cells were subjected to either pressure [0, 60 or 90 mmHg] or static stretch [0 or 20%] for 24 or 48 h. Cell proliferation was measured by cell counting, cell cycle analyzed by flow cytometry, and PCNA and Skp2 expression were determined by qPCR or western blot. Blood gases were determined in an iSTAT system. Proliferation was also assessed in vivo after 24 h of ureteral obstruction. There was a significant increase in HKC-8 cell number after 48 h of exposure to either 60 or 90 mmHg pressure. Western blot and qPCR confirmed increased expression of PCNA and Skp2 in pressurized cells. Cell cycle measurements demonstrated an increase in HKC-8 in S phase. Mechanical stretching increased PCNA protein expression in HKC-8 cells after 48 h while no effect was observed on Skp2 and cell cycle measurements. Increased PCNA expression was found at 24 h after ureteral obstruction. We demonstrate direct transduction of pressure into a proliferative response in HKC-8 and NRK-52E cells, measured by cell number, PCNA and Skp2 expression and increase in cells in S phase, whereas stretch had a less robust effect on proliferation.

Dynamic changes of early-stage aortic lipid deposition in chronic renal failure rats and effects of decorin gene therapy

The aim of the present study was to clarify the association between lipid metabolism and the atherosclerosis in early-stage chronic renal failure at the molecular level and to explore the efficacy of decorin on chronic renal failure. Sprague Dawley rats receiving 5/6 nephrectomy and Sham surgery were divided into control and experimental groups. Sprague Dawley rats receiving 5/6 nephrectomy were divided into control and experimental groups, and the experimental group was further subdivided into rats receiving treatment with fibroblasts (FBs) transfected either with empty vector and with a decorin (DCN) gene. The dynamic levels of triglyceride (TG), total cholesterol (T-Ch) and total phospholipid (T-PL) were detected on the 10th, 30th and 60th days. The body weight, blood lipid levels, renal function and renal tissue were observed after four weeks, and transforming growth factor-βl and protein expression was detected by immunohistochemistry. In total, 4 weeks after treatment, the DCN expression in the renal tissue of rats treated with DCN-transfected FBs was significantly increased compared to that in the control rats. The results showed that the levels of the three lipids in the aortic arches were slightly elevated on the 10th day compared with those in the control group, and the TG level was significantly increased on the 30th day. The levels of T-Ch, TG and T-PL in the aortic arches were significantly elevated on the 60th day. The TG and T-Ch levels in the plasma and aortic tissues of Sprague Dawley rats receiving 5/6 nephrectomy without any treatment and after receiving treatment with FBs transfected with empty vector were significantly increased compared with those in the control group. The increased T-Ch and decreased T-PL levels in the erythrocyte membrane increased the rigidity of the erythrocyte and decreased erythrocyte deformability. In conclusion, highly expressed DCN mitigated renal fibrosis and thus delayed renal failure as well as mitigating the abnormal lipid metabolism of the chronic renal failure.