Growth hormone exacerbates diabetic renal damage in male but not female rats

Insight into the Molecular Mechanism of Diabetic Kidney Disease and the Role of Metformin in Its Pathogenesis

Diabetic kidney disease (DKD) is one of the leading causes of death among patients diagnosed with diabetes mellitus. Despite the growing knowledge about the pathogenesis of DKD, we still do not have effective direct pharmacotherapy. Accurate blood sugar control is essential in slowing down DKD. It seems that metformin has a positive impact on kidneys and this effect is not only mediated by its hypoglycemic action, but also by direct molecular regulation of pathways involved in DKD. The molecular mechanism of DKD is complex and we can distinguish polyol, hexosamine, PKC, and AGE pathways which play key roles in the development and progression of this disease. Each of these pathways is overactivated in a hyperglycemic environment and it seems that most of them may be regulated by metformin. In this article, we summarize the knowledge about DKD pathogenesis and the potential mechanism of the nephroprotective effect of metformin. Additionally, we describe the impact of metformin on glomerular endothelial cells and podocytes, which are harmed in DKD.

Sex-Mediated Differences in TNF Signaling- and ECM-Related Gene Expression in Aged Rat Kidney

Aging leads to the functional decline of an organism, which is associated with age and sex. To understand the functional change of kidneys depending on age and sex, we carried out a transcriptome analysis using RNA sequencing (RNA-Seq) data from rat kidneys. Four differentially expressed gene (DEG) sets were generated according to age and sex, and Gene Ontology analysis and overlapping analysis of Kyoto Encyclopedia of Genes and Genomes pathways were performed for the DEG sets. Through the analysis, we revealed that inflammation- and extracellular matrix (ECM)-related genes and pathways were upregulated in both males and females during aging, which was more prominent in old males than in old females. Furthermore, quantitative real-time PCR analysis confirmed that the expression of tumor necrosis factor (TNF) signaling-related genes, Birc3, Socs3, and Tnfrsf1b, and ECM-related genes, Cd44, Col3a1, and Col5a2, which showed that the genes were markedly upregulated in males and not females during aging. Also, hematoxylin-eosin (H&E) staining for histological analysis showed that renal damage was highly shown in old males rather than old females. In conclusion, in the rat kidney, the genes involved in TNF signaling and ECM accumulation are upregulated in males more than in females during aging. These results suggest that the upregulation of the genes may have a higher contribution to age-related kidney inflammation and fibrosis in males than in females.

Podocyte derived TNF-α mediates monocyte differentiation and contributes to glomerular injury

Diabetes shortens the life expectancy by more than a decade, and the excess mortality in diabetes is correlated with the incidence of kidney disease. Diabetic kidney disease (DKD) is the leading cause of end-stage kidney disease. Macrophage accumulation predicts the severity of kidney injury in human biopsies and experimental models of DKD. However, the mechanism underlying macrophage recruitment in diabetes glomeruli is unclear. Elevated plasma growth hormone (GH) levels in type I diabetes and acromegalic individuals impaired glomerular biology. In this study, we examined whether GH-stimulated podocytes contribute to macrophage accumulation. RNA-seq analysis revealed elevated TNF-α signaling in GH-treated human podocytes. Conditioned media from GH-treated podocytes (GH-CM) induced differentiation of monocytes to macrophages. On the other hand, neutralization of GH-CM with the TNF-α antibody diminished GH-CM's action on monocytes. The treatment of mice with GH resulted in increased macrophage recruitment, podocyte injury, and proteinuria. Furthermore, we noticed the activation of TNF-α signaling, macrophage accumulation, and fibrosis in DKD patients' kidney biopsies. Our findings suggest that podocytes could secrete TNF-α and contribute to macrophage migration, resulting in DKD-related renal inflammation. Inhibition of either GH action or TNF-α expression in podocytes could be a novel therapeutic approach for DKD treatment.

Growth hormone induces mitotic catastrophe of glomerular podocytes and contributes to proteinuria

Glomerular podocytes are integral members of the glomerular filtration barrier in the kidney and are crucial for glomerular permselectivity. These highly differentiated cells are vulnerable to an array of noxious stimuli that prevail in several glomerular diseases. Elevated circulating growth hormone (GH) levels are associated with podocyte injury and proteinuria in diabetes. However, the precise mechanism(s) by which excess GH elicits podocytopathy remains to be elucidated. Previous studies have shown that podocytes express GH receptor (GHR) and induce Notch signaling when exposed to GH. In the present study, we demonstrated that GH induces TGF-β1 signaling and provokes cell cycle reentry of otherwise quiescent podocytes. Though differentiated podocytes reenter the cell cycle in response to GH and TGF-β1, they cannot accomplish cytokinesis, despite karyokinesis. Owing to this aberrant cell cycle event, GH- or TGF-β1-treated cells remain binucleated and undergo mitotic catastrophe. Importantly, inhibition of JAK2, TGFBR1 (TGF-β receptor 1), or Notch prevented cell cycle reentry of podocytes and protected them from mitotic catastrophe associated with cell death. Inhibition of Notch activation prevents GH-dependent podocyte injury and proteinuria. Similarly, attenuation of GHR expression abated Notch activation in podocytes. Kidney biopsy sections from patients with diabetic nephropathy (DN) show activation of Notch signaling and binucleated podocytes. These data indicate that excess GH induced TGF-β1-dependent Notch1 signaling contributes to the mitotic catastrophe of podocytes. This study highlights the role of aberrant GH signaling in podocytopathy and the potential application of TGF-β1 or Notch inhibitors, as a therapeutic agent for DN.

Maternal undernutrition results in altered renal pro-inflammatory gene expression concomitant with hypertension in adult male offspring that is ameliorated following pre-weaning growth hormone treatment

An adverse early life environment is associated with increased cardiovascular disease in offspring. Work in animal models has shown that maternal undernutrition (UN) during pregnancy leads to hypertension in adult offspring, with effects thought to be mediated in part via altered renal function. We have previously shown that growth hormone (GH) treatment of UN offspring during the pre-weaning period can prevent the later development of cardiometabolic disorders. However, the mechanistic basis for these observations is not well defined. The present study examined the impact of GH treatment on renal inflammatory markers in adult male offspring as a potential mediator of these reversal effects. Female Sprague-Dawley rats were fed either a chow diet fed ad libitum (CON) or at 50% of CON intake (UN) during pregnancy. All dams were fed the chow diet ad libitum during lactation. CON and UN pups received saline (CON-S/UN-S) or GH (2.5 µg/g/day; CON-GH/UN-GH) from postnatal day 3 until weaning (p21). Post-weaning males were fed a standard chow diet for the remainder of the study (150 days). Histological analysis was performed to examine renal morphological characteristics, and gene expression of inflammatory and vascular markers were assessed. There was evidence of renal hypotrophy and reduced nephron number in the UN-S group. Tumour necrosis factor-α, monocyte chemoattractant protein-1 (MCP-1), intercellular adhesion molecular-1 and vascular cell adhesion molecule-1 gene expression was increased in UN-S offspring and normalized in the UN-GH group. These findings indicate that pre-weaning GH treatment has the potential to normalize some of the adverse renal and cardiovascular sequelae that arise as a consequence of poor maternal nutrition.

Growth hormone induces Notch1 signaling in podocytes and contributes to proteinuria in diabetic nephropathy

Growth hormone (GH) plays a significant role in normal renal function and overactive GH signaling has been implicated in proteinuria in diabetes and acromegaly. Previous results have shown that the glomerular podocytes, which play an essential role in renal filtration, express the GH receptor, suggesting the direct action of GH on these cells. However, the exact mechanism and the downstream pathways by which excess GH leads to diabetic nephropathy is not established. In the present article, using immortalized human podocytes in vitro and a mouse model in vivo, we show that excess GH activates Notch1 signaling in a γ-secretase-dependent manner. Pharmacological inhibition of Notch1 by γ-secretase inhibitor DAPT (N-[N-(3,5-Difluorophenacetyl)-l-alanyl]-S-phenyl glycine t-butylester) abrogates GH-induced epithelial to mesenchymal transition (EMT) and is associated with a reduction in podocyte loss. More importantly, our results show that DAPT treatment blocks cytokine release and prevents glomerular fibrosis, all of which are induced by excess GH. Furthermore, DAPT prevented glomerular basement membrane thickening and proteinuria induced by excess GH. Finally, using kidney biopsy sections from people with diabetic nephropathy, we show that Notch signaling is indeed up-regulated in such settings. All these results confirm that excess GH induces Notch1 signaling in podocytes, which contributes to proteinuria through EMT as well as renal fibrosis. Our studies highlight the potential application of γ-secretase inhibitors as a therapeutic target in people with diabetic nephropathy.

Sex hormones and their influence on chronic kidney disease

PURPOSE OF REVIEW

The majority of end-stage renal disease including dialysis and kidney transplant patients are men. In contrast, the incidence of chronic kidney disease (CKD) is higher in women compared with men. In this review, we dissect the sex hormone levels and its effects on experimental models and patients with CKD.

RECENT FINDINGS

Sex hormones are clearly involved in CKD progression to end-stage renal disease (ESRD). A significant reduction in lipid peroxidation as a mechanism of renoprotection has been observed in kidneys of streptozotocin (STZ)-diabetic ovariectomized rats after estradiol administration. Furthermore, a G-protein-coupled estrogen receptor inhibits podocyte oxidative stress maintaining the integrity of the mitochondrial membrane. Sex hormone depletion has been shown to modulate RAS system and protect against kidney injury in the male STZ-diabetic model. In human primary proximal tubular epithelial cells, a proteomic study showed that dihydrotestosterone dysregulated metabolic, suggesting that the deleterious effect of androgens within the kidney maybe related to altered energy metabolism in renal tubules.

SUMMARY

Male gender is associated with worse CKD progression and this fact may be ascribed to sex hormone. Although male hormones exert a deleterious effect in terms of increasing oxidative stress, activating RAS system, and worsening fibrosis within the damaged kidney, female hormones exert a renoprotective effect.

Growth hormone and chronic kidney disease

PURPOSE OF REVIEW

Elevated circulating levels of growth hormone (GH) and/or increased expression of the GH receptor in the kidney are associated with the development of nephropathy in type1 diabetes and acromegaly. Conditions of GH excess are characterized by hyperfiltration, glomerular hypertrophy, glomerulosclerosis and albuminuria, whereas states of decreased GH secretion or action are protected against glomerulopathy. The direct role of GH's action on glomerular cells, particularly podocytes, has been the focus of recent studies. In this review, the emerging role of GH on the biological function of podocytes and its implications in the pathogenesis of diabetic and chronic kidney disease will be discussed.

RECENT FINDINGS

Elevated GH levels impair glomerular permselectivity by altering the expression of podocyte slit-diaphragm proteins. GH stimulates the epithelial-mesenchymal transition of podocytes and decreases podocyte count. GH also induces the expression of prosclerotic molecules transforming growth factor beta, and TGFBIp.

SUMMARY

Our understanding of the cellular and molecular effects of GH in the pathogenesis of renal complications of diabetes and acromegaly has significantly progressed in recent years. These observations open up new possibilities in the prevention and treatment of diabetic nephropathy.

Endocytosis of Albumin Induces Matrix Metalloproteinase-9 by Activating the ERK Signaling Pathway in Renal Tubule Epithelial Cells

Matrix metalloproteinase-9 (MMP-9) is dysregulated in chronic kidney diseases including diabetic nephropathy. This study was performed to examine the expression of MMP-9 in renal tubule epithelial cells (TECs) under diabetic conditions and its regulatory mechanisms. We characterized MMP-9 protein in diabetic animals and primary cultured rat TECs exposed to exogenous albumin and high glucose. We also used specific inhibitors to determine if internalization of albumin and/or extracellular signal-regulated kinase 1/2 (ERK1/2) phosphorylation were required for MMP-9 secretion. Immunostaining of kidney sections revealed enhanced MMP-9 signal in the damaged proximal tubules in Zucker diabetic fatty (ZDF) rats. ZDF rats also exhibited an albuminuria-related and age-dependent increase in MMP-9 excretion, which was prevented by rosiglitazone. In primary cultured rat TECs, high glucose exposure did not increase MMP-9 secretion. In contrast, administration of rat serum albumin (RSA, 0.1–0.5 mg/mL) resulted in a dose-dependent increase in MMP-9 expression and secretion by TECs, which was abolished in the presence of an ERK1/2-specific inhibitor, U0126. Simvastatin, an inhibitor of albumin endocytosis, also prevented MMP-9 secretion. Taken together, these results demonstrate that endocytosis of albumin stimulates MMP-9 secretion by TECs through the ERK signaling pathway.

Novel Actions of Growth Hormone in Podocytes: Implications for Diabetic Nephropathy

The kidney regulates water, electrolyte, and acid-base balance and thus maintains body homeostasis. The kidney’s potential to ensure ultrafiltered and almost protein-free urine is compromised in various metabolic and hormonal disorders such as diabetes mellitus (DM). Diabetic nephropathy (DN) accounts for ~20–40% of mortality in DM. Proteinuria, a hallmark of renal glomerular diseases, indicates injury to the glomerular filtration barrier (GFB). The GFB is composed of glomerular endothelium, basement membrane, and podocytes. Podocytes are terminally differentiated epithelial cells with limited ability to replicate. Podocyte shape and number are both critical for the integrity and function of the GFB. Podocytes are vulnerable to various noxious stimuli prevalent in a diabetic milieu that could provoke podocytes to undergo changes to their unique architecture and function. Effacement of podocyte foot process is a typical morphological alteration associated with proteinuria. The dedifferentiation of podocytes from epithelial-to-mesenchymal phenotype and consequential loss results in proteinuria. Poorly controlled type 1 DM is associated with elevated levels of circulating growth hormone (GH), which is implicated in the pathophysiology of various diabetic complications including DN. Recent studies demonstrate that functional GH receptors are expressed in podocytes and that GH may exert detrimental effects on the podocyte. In this review, we summarize recent advances that shed light on actions of GH on the podocyte that could play a role in the pathogenesis of DN.

Matrix Metalloproteinases in Kidney Disease: Role in Pathogenesis and Potential as a Therapeutic Target

Matrix metalloproteinases (MMPs) are large family of proteinases. In addition to a fundamental role in the remodeling of the extracellular matrix, they also cleave a number of cell surface proteins and are involved in multiple cellular processes. MMP activity is regulated via numerous mechanisms, including inhibition by endogenous tissue inhibitors of metalloproteinases (TIMPs). Similar to MMPs, a role for TIMPs has been established in multiple cell signaling pathways. Aberrant expression of MMPs and TIMPS in renal pathophysiology has long been recognized, and with the generation of specific knockout mice, the mechanistic role of several MMPs and TIMPs is becoming more understood and has revealed both pathogenic and protective roles. This chapter will focus on the expression and localization of MMPs and TIMPs in the kidney, as well as summarizing the current information linking these proteins to acute kidney injury and chronic kidney disease. In addition, we will summarize studies suggesting that MMPs and TIMPs may be biomarkers of renal dysfunction and represent novel therapeutic targets to attenuate kidney disease.

Matrix metalloproteinase-9 expression is enhanced in renal parietal epithelial cells of zucker diabetic Fatty rats and is induced by albumin in in vitro primary parietal cell culture

As a subfamily of matrix metalloproteinases (MMPs), gelatinases including MMP-2 and MMP-9 play an important role in remodeling and homeostasis of the extracellular matrix. However, conflicting results have been reported regarding their expression level and activity in the diabetic kidney. This study investigated whether and how MMP-9 expression and activity were changed in glomerular epithelial cells upon albumin overload. In situ zymography, immunostaining and Western blot for renal MMP gelatinolytic activity and MMP-9 protein expression were performed in Zucker lean and Zucker diabetic rats. Confocal microscopy revealed a focal increase in gelatinase activity and MMP-9 protein in the glomeruli of diabetic rats. Increased glomerular MMP-9 staining was mainly observed in hyperplastic parietal epithelial cells (PECs) expressing claudin-1 in the diabetic kidneys. Interestingly, increased parietal MMP-9 was often accompanied by decreased staining for podocyte markers (nephrin and podocalyxin) in the sclerotic area of affected glomeruli in diabetic rats. Additionally, urinary excretion of podocyte marker proteins was significantly increased in association with the levels of MMP-9 and albumin in the urine of diabetic animals. To evaluate the direct effect of albumin on expression and activity of MMP-9, primary cultured rat glomerular PECs were incubated with rat serum albumin (0.25 - 1 mg/ml) for 24 - 48 hrs. MMP-9 mRNA levels were significantly increased following albumin treatment. Meanwhile, albumin administration resulted in a dose-dependent increase in MMP-9 protein and activity in culture supernatants of PECs. Moreover, albumin activated p44/42 mitogen-activated protein kinase (MAPK) in PECs. Inhibition of p44/42 MAPK suppressed albumin-induced MMP-9 secretion from glomerular PECs. Taken together, we have demonstrated that an up-regulation of MMP-9 in activated parietal epithelium is associated with a loss of adjacent podocytes in progressive diabetic nephropathy. Albumin overload may induce MMP-9 expression and secretion by PECs via the activation of p44/42 MAPK pathway.