Parathyroid hormone-related protein is a hypertrophy factor for human mesangial cells: Implications for diabetic nephropathy

Parathyroid Hormone Related Protein (PTHrP)-Associated Molecular Signatures in Tissue Differentiation and Non-Tumoral Diseases

Parathyroid-hormone-related protein (PTHrP) is encoded by the PTHLH gene which, via alternative promoter usage and splicing mechanisms, can give rise to at least three isoforms of 139, 141, and 173 amino acids with distinct C-terminals. PTHrP is subjected to different post-translational processing that generates smaller bioactive forms, comprising amino terminus, mid-region (containing a nuclear/nucleolar targeting signal), and carboxy terminus peptides. Both the full-length protein and the discrete peptides are key controllers of viability, proliferation, differentiation, and apoptosis in diverse normal and pathological biological systems via the reprogramming of gene expression and remodulation of PKA or PKC-mediated signalization mechanisms. The aim of this review is to pick up selected studies on PTHrP-associated signatures as revealed by molecular profiling assays, focusing on the available data about exemplary differentiating, differentiated, or nontumoral cell and tissue models. In particular, the data presented relate to adipose, bone, dental, cartilaginous, and skin tissues, as well as intestinal, renal, hepatic, pulmonary, and pancreatic epithelia, with a focus on hepatic fibrosis-, pancreatitis-, and diabetes-related changes as diseased states. When reported, the biochemical and/or physiological aspects associated with the specific molecular modulation of gene expression and signal transduction pathways in the target model systems under examination are also briefly described.

Comparison of the renal effects of bisphenol A in mice with and without experimental diabetes. Role of sexual dimorphism

Bisphenol-A (BPA), a chemical -xenoestrogen- used in the production of the plastic lining of food and beverage containers, is present in the urine of almost the entire population. Recent studies have shown that BPA exposure is associated with podocytopathy, increased urinary albumin excretion (UAE), and hypertension. Since these changes are characteristic of early diabetic nephropathy (DN), we explored the renal effects of BPA and diabetes including the potential role of sexual dimorphism. Male and female mice were included in the following animals' groups: control mice (C), mice treated with 21.2 mg/kg of BPA in the drinking water (BPA), diabetic mice induced by streptozotocin (D), and D mice treated with BPA (D + BPA). Male mice form the D + BPA group died by the tenth week of the study due probably to hydro-electrolytic disturbances. Although BPA treated mice did not show an increase in serum creatinine, as observed in D and D + BPA groups, they displayed similar alteration to those of the D group, including increased in kidney damage biomarkers NGAL and KIM-1, UAE, hypertension, podocytopenia, apoptosis, collapsed glomeruli, as well as TGF-β, CHOP and PCNA upregulation. UAE, collapsed glomeruli, PCNA staining, TGF-β, NGAL and animal survival, significantly impaired in D + BPA animals. Moreover, UAE, collapsed glomeruli and animal survival also displayed a sexual dimorphism pattern. In conclusion, oral administration of BPA is capable of promoting in the kidney alterations that resemble early DN. Further translational studies are needed to clarify the potential role of BPA in renal diseases, particularly in diabetic patients.

Dysregulation of miR-638 in diabetic nephropathy and its role in inflammatory response

BACKGROUND

MicroRNA (miRNA) can be used as a biomarker for the early diagnosis of diabetic nephropathy (DN). The purpose of this study was to evaluate the diagnostic value of miR-638 in DN and to analyse its regulatory effect on inflammation.

METHODS

This retrospective study involved 98 subjects, including non-diabetic healthy controls (n = 30), patients with type 2 diabetes (T2DM, n = 36) without complications and patients with DN (n = 32). After the anthropometric and biochemical evaluation, serum miR-638 levels were assessed by real-time reverse transcription-polymerase chain reaction (qRT-PCR). The levels of inflammatory cytokines (interleukin [IL]-1β, IL-6, and tumor necrosis factor-alpha [TNF-α]) were detected using enzyme-linked immunosorbent assay. The Spearman correlations were used to analyze the correlation between miR-638 and urinary albumin excretion (UAE), estimated glomerular filtration rate (eGFR), and inflammatory factors. Furthermore, the receiver operating characteristic (ROC) curve was used to measure the diagnostic value of miR-638 in DN. Human mesangial cells (HMCs) were treated with normal glucose (NG, 5.5 mM glucose), high glucose (HG, 30 mM glucose), or high osmotic pressure solution (HO, 5.5 mM glucose + 24.5 mM mannitol) in vitro to simulate the hyperglycamic state in vivo. Subsequently, the HMCs were transfected with miR-638 mimics to regulate the level of miR-638 in the cells and detect its regulation on cell inflammation and proliferation.

RESULTS

Compared with healthy controls and patients with T2DM, serum miR-638 in patients with DN was significantly lower. The reduced miR-638 expression has a significant diagnostic value, which can significantly distinguish patients with DN from healthy controls or patients with T2DM. Inflammatory factors were significantly upregulated in patients with DN and negatively correlated with miR-638 levels. In addition, miR-638 was negatively correlated with UAE and positively correlated with eGFR. HG decreased the level of miR-638 and promoted the expression of inflammatory factors and proliferation in HMCs. However, miR-638 mimic significantly decreased the levels of inflammatory factors and inhibited the proliferative ability induced by HG.

CONCLUSIONS

Serum miR-638 expression was low in DN and can be a potentially valuable biomarker for DN. This miRNA seems to influence inflammatory responses and participate in the progression of DN by regulating proliferation.

CDK9 inhibition improves diabetic nephropathy by reducing inflammation in the kidneys

Diabetic nephropathy (DN) is a chronic inflammatory renal disease induced by hyperglycemia. Recent studies have implicated cyclin-dependent kinase 9 (CDK9) in inflammatory responses and renal fibrosis. In this study, we explored a potential role of CDK9 in DN by using cultured mouse mesangial cell line SV40 MES-13 and streptozotocin-induced type 1 mouse model of diabetes. We inhibited CDK9 in mice and in cultured cells by a highly selective CDK9 inhibitor, LDC000067 (LDC), and evaluated inflammatory and fibrogenic outcome by mRNA and protein analyses. Our studies show that treatment of diabetic mice with LDC significantly inhibits the levels of inflammatory cytokines and fibrogenic genes in kidney specimens. These reductions were associated with improved renal function. We also found that LDC treatment suppressed MAPK-AP1 activation. We then confirmed the involvement of CDK9 in cultured SV40 MES-13 cells and showed that deficiency in CDK9 prevents glucose-induced inflammatory and fibrogenic proteins. This protection was also afforded by suppression of MAPK-AP1. Taken together, our results how that hyperglycemia activates CDK9-MAPK-AP1 axis in kidneys to induce inflammation and fibrosis, leading to renal dysfunction. Our findings also suggest that CDK9 may serve as a potential therapeutic target for DN.

Bisphenol A impaired cell adhesion by altering the expression of adhesion and cytoskeleton proteins on human podocytes

Bisphenol A (BPA), a chemical -xenoestrogen- used in food containers is present in the urine of almost the entire population. Recently, several extensive population studies have proven a significant association between urinary excretion of BPA and albuminuria. The alteration of glomerular podocytes or "podocytopathy" is a common event in chronic albuminuric conditions. Since many podocytes recovered from patients' urine are viable, we hypothesized that BPA could impair podocyte adhesion capabilities. Using an in vitro adhesion assay, we observed that BPA impaired podocyte adhesion, an effect that was abrogated by Tamoxifen (an estrogen receptor blocker). Genomic and proteomic analyses revealed that BPA affected the expression of several podocyte cytoskeleton and adhesion proteins. Western blot and immunocytochemistry confirmed the alteration in the protein expression of tubulin, vimentin, podocin, cofilin-1, vinculin, E-cadherin, nephrin, VCAM-1, tenascin-C, and β-catenin. Moreover, we also found that BPA, while decreased podocyte nitric oxide production, it lead to overproduction of ion superoxide. In conclusion, our data show that BPA induced a novel type of podocytopathy characterizes by an impairment of podocyte adhesion, by altering the expression of adhesion and cytoskeleton proteins. Moreover, BPA diminished production of podocyte nitric oxide and induced the overproduction of oxygen-free metabolites. These data provide a mechanism by which BPA could participate in the pathogenesis and progression of renal diseases.

Urinary excretion of parathyroid hormone-related protein correlates with renal function in control rats and rats with cisplatin nephrotoxicity

Parathyroid hormone-related protein (PTHrP) and its receptor are abundantly expressed throughout the renal parenchyma, where PTHrP exerts a modulatory action on renal function. PTHrP upregulation is a common event associated with the mechanism of renal injury and repair. However, no study has yet explored the putative excretion of PTHrP in urine, including its potential relationship with renal function. In the present study, we tested this hypothesis by studying the well-known rat model of acute renal injury induced by the chemotherapeutic agent cisplatin. Using Western blot analysis, we could detect a single protein band, corresponding to intact PTHrP, in the urine of both control and cisplatin-injected rats, whose levels were significantly higher in the latter group. PTHrP was detected in rat urine by dot blot, and its quantification with two specific ELISA kits showed that, compared with control rats, those treated with cisplatin displayed a significant increase in urinary PTHrP (expressed as the PTHrP-to-creatinine ratio or 24-h excretion). In addition, a positive correlation between urinary PTHrP excretion and serum creatinine was found in these animals. In conclusion, our data demonstrate that PTHrP is excreted in rat urine and that this excretion is higher with the decrease of renal function. This suggests that urinary PTHrP levels might be a renal function marker.

Parathyroid hormone-related protein induces fibronectin up-regulation in rat mesangial cells through reactive oxygen species/Src/EGFR signaling

Parathyroid hormone-related protein (PTHrP) is known to be up-regulated in both glomeruli and tubules in patients with diabetic kidney disease (DKD), but its role remains unclear. Previous studies show that PTHrP-induced hypertrophic response in mesangial cells (MCs) and epithelial-mesenchymal transition (EMT) in tubuloepithelial cells can be mediated by TGF-β1. In the present study, although long-term PHTrP (1-34) treatment increased the mRNA and protein level of TGF-β1 in primary rat MCs, fibronectin up-regulation occurred earlier, suggesting that fibronectin induction is independent of TGF-β1/Smad signaling. We thus evaluated the involvement of epidermal growth factor receptor (EGFR) signaling and found that nicotinamide adenine dinucleotide phosphate oxidase-derived reactive oxygen species mediates PTHrP (1-34)-induced Src kinase activation. Src phosphorylates EGFR at tyrosine 845 and then transactive EGFR. Subsequent PI3K activation mediates Akt and ERK1/2 activation. Akt and ERK1/2 discretely lead to excessive protein synthesis of fibronectin. Our study thus demonstrates the new role of PTHrP in fibronectin up-regulation for the first time in glomerular MCs. These data also provided new insights to guide development of therapy for glomerular sclerosis.

The influence of fasudil on renal proximal tubular cell epithelial-mesenchymal transition induced by parathormone

BACKGROUND

Renal fibrosis is a common pathway through which a variety of chronic kidney diseases progress to end-stage renal disease. Epithelial-mesenchymal transition (EMT) of renal proximal tubular cells is one of the most important factors in renal fibrosis. This study investigates if fasudil could influence EMT of renal proximal tubular cells.

METHODS

HK-2 cells in passage 3-4 were used for all experiments. The cells were divided into five groups and treated with different concentrations of PTH and then observe cellular morphological changes at 0, 24 and 48 h using an inverted microscope and investigate the expression of the epithelial cell marker E-cadherin and the renal fibroblast marker α-smooth muscle actin (α-SMA).

RESULTS

PTH significantly induced EMT, fasudil-inhibited EMT induced by PTH to different degrees, and the inhibitory effect of fasudil was most pronounced at 20 μmol/L.

CONCLUSION

Monitoring PTH levels, early prevention and control of hyperparathyroidism and reducing the concentration of PTH are important means to improve prognosis and delay the progression of chronic kidney disease. Fasudil can restrain EMT induced by PTH; this conclusion provides experimental data for the application of fasudil in the clinical prevention and treatment of renal fibrosis.

Parathyroid hormone-related protein modulates inflammation in mouse mesangial cells and blunts apoptosis by enhancing COX-2 expression

Injury of mesangial cells (MC) is a prominent feature of glomerulonephritis. Activated MC secrete inflammatory mediators that induce cell apoptosis. Parathyroid hormone-related peptide (PTHrP) is a locally active cytokine that enhances cell survival and is upregulated by proinflammatory factors in many cell types. The aim of this study was to analyze the regulation of PTHrP expression by inflammatory cytokines and to evaluate whether PTHrP itself acts as a proinflammatory and/or survival factor on male murine MC in primary culture. Our results showed that IL-1β (10 ng/ml) and TNF-α (10 ng/ml) rapidly and transiently upregulated PTHrP expression in MC. The effects of IL-1β were both transcriptional and posttranscriptional, with stabilization of the PTHrP mRNA by human antigen R (HuR). Proteome profiler arrays showed that PTHrP itself enhanced cytokines within 2 h in cell lysates, mainly IL-17, IL-16, IL-1α, and IL-6. PTHrP also stimulated sustained expression (2-4 h) of chemokines, mainly regulated upon activation normal T cell expressed and secreted (RANTES)/C-C motif chemokine 5 (CCL5) and macrophage inflammatory protein-2 (MIP-2)/C-X-C motif chemokine 2 (CXCL2), thymus and activation-regulated chemokine (TARC)/CCL17, and interferon-inducible T cell α-chemoattractant (I-TAC)/CXCL11. Moreover, PTHrP markedly enhanced cyclooxygenase-2 (COX-2) expression and elicited its autoinduction through the activation of the NF-κB pathway. PTHrP induced MC survival via the COX-2 products, and PTHrP overexpression in MC blunted the apoptotic effects of IL-1β and TNF-α. Altogether, these findings suggest that PTHrP functions as a booster of glomerular inflammatory processes and may be a negative feedback loop preserving MC survival.

Dual roles of parathyroid hormone related protein in TGF-β1 signaling and fibronectin up-regulation in mesangial cells

Little is known about the cross-talk between parathyroid hormone (PTH) related protein (PTHrP) and TGF-β1 in mesangial cells (MCs). Our results showed that PTHrP treatment (≤3 h) induced internalization of PTH1R (PTH/PTHrP receptor)–TβRII (TGF-β type 2 receptor) complex and suppressed TGF-β1-mediated Smad2/3 activation and fibronectin (FN) up-regulation. However, prolonged PTHrP treatment (12–48 h) failed to induce PTH1R–TβRII association and internalization. Total protein levels of PTH1R and TβRII were unaffected by PTHrP treatment. These results suggest that internalization of PTH1R and TβRII after short PTHrP treatment might not lead to their proteolytic destruction, allowing the receptors to be recycled back to the plasma membrane during prolonged PTHrP exposure. Receptor re-expression at the cell surface allows PTHrP to switch from its initial inhibitory effect to promote induction of FN. Our study thus demonstrates the dual roles of PTHrP on TGF-β1 signaling and FN up-regulation for the first time in glomerular MCs. These data also provided new insights to guide development of therapy for diabetic kidney disease (DKD).

Bisphenol-A induces podocytopathy with proteinuria in mice

Bisphenol-A, a chemical used in the production of the plastic lining of food and beverage containers, can be found in significant levels in human fluids. Recently, bisphenol-A has been associated with low-grade albuminuria in adults as well as in children. Since glomerular epithelial cells (podocytes) are commonly affected in proteinuric conditions, herein we explored the effects of bisphenol-A on podocytes in vitro and in vivo. On cultured podocytes we first observed that bisphenol-A-at low or high concentrations-(10 nM and 100 nM, respectively) was able to induce hypertrophy, diminish viability, and promote apoptosis. We also found an increase in the protein expression of TGF-β1 and its receptor, the cyclin-dependent kinase inhibitor p27Kip1, as well as collagen-IV, while observing a diminished expression of the slit diaphragm proteins nephrin and podocin. Furthermore, mice intraperitoneally injected with bisphenol-A (50 mg/Kg for 5 weeks) displayed an increase in urinary albumin excretion and endogenous creatinine clearance. Renal histology showed mesangial expansion. At ultrastructural level, podocytes displayed an enlargement of both cytoplasm and foot processes as well as the presence of condensed chromatin, suggesting apoptosis. Furthermore, immunohistochemistry for WT-1 (specific podocyte marker) and the TUNEL technique showed podocytopenia as well as the presence of apoptosis, respectively. In conclusion, our data demonstrate that Bisphenol-A exposure promotes a podocytopathy with proteinuria, glomerular hyperfiltration and podocytopenia. Further studies are needed to clarify the potential role of bisphenol-A in the pathogenesis as well as in the progression of renal diseases.

Parathyroid hormone-related protein is a mitogenic and a survival factor of mesangial cells from male mice: role of intracrine and paracrine pathways

Glomerulonephritis is characterized by the proliferation and apoptosis of mesangial cells (MC). The parathyroid-hormone related protein (PTHrP) is a locally active cytokine that affects these phenomena in many cell types, through either paracrine or intracrine pathways. The aim of this study was to evaluate the effect of both PTHrP pathways on MC proliferation and apoptosis. In vitro studies were based on MC from male transgenic mice allowing PTHrP-gene excision by a CreLoxP system. MC were also transfected with different PTHrP constructs: wild type PTHrP, PTHrP devoid of its signal peptide, or of its nuclear localization sequence. The results showed that PTHrP deletion in MC reduced their proliferation even in the presence of serum and increased their apoptosis when serum-deprived. PTH1R activation by PTHrP(1-36) or PTH(1-34) had no effect on proliferation but improved MC survival. Transfection of MC with PTHrP devoid of its signal peptide significantly increased their proliferation and minimally reduced their apoptosis. Overexpression of PTHrP devoid of its nuclear localization sequence protected cells from apoptosis without changing their proliferation. Wild type PTHrP transfection conferred both mitogenic and survival effects, which seem independent of midregion and C-terminal PTHrP fragments. PTHrP-induced MC proliferation was associated with p27(Kip1) down-regulation and c-Myc/E2F1 up-regulation. PTHrP increased MC survival through the activation of cAMP/protein kinase A and PI3-K/Akt pathways. These results reveal that PTHrP is a cytokine of multiple roles in MC, acting as a mitogenic factor only through an intracrine pathway, and reducing apoptosis mainly through the paracrine pathway. Thus, PTHrP appears as a probable actor in MC injuries.