The glomerular podocyte as a target of growth hormone action: implications for the pathogenesis of diabetic nephropathy

Longitudinal metabolite and protein trajectories prior to diabetes mellitus diagnosis in Danish blood donors: a nested case-control study

AIMS/HYPOTHESIS

Metabolic risk factors and plasma biomarkers for diabetes have previously been shown to change prior to a clinical diabetes diagnosis. However, these markers only cover a small subset of molecular biomarkers linked to the disease. In this study, we aimed to profile a more comprehensive set of molecular biomarkers and explore their temporal association with incident diabetes.

METHODS

We performed a targeted analysis of 54 proteins and 171 metabolites and lipoprotein particles measured in three sequential samples spanning up to 11 years of follow-up in 324 individuals with incident diabetes and 359 individuals without diabetes in the Danish Blood Donor Study (DBDS) matched for sex and birth year distribution. We used linear mixed-effects models to identify temporal changes before a diabetes diagnosis, either for any incident diabetes diagnosis or for type 1 and type 2 diabetes mellitus diagnoses specifically. We further performed linear and non-linear feature selection, adding 28 polygenic risk scores to the biomarker pool. We tested the time-to-event prediction gain of the biomarkers with the highest variable importance, compared with selected clinical covariates and plasma glucose.

RESULTS

We identified two proteins and 16 metabolites and lipoprotein particles whose levels changed temporally before diabetes diagnosis and for which the estimated marginal means were significant after FDR adjustment. Sixteen of these have not previously been described. Additionally, 75 biomarkers were consistently higher or lower in the years before a diabetes diagnosis. We identified a single temporal biomarker for type 1 diabetes, IL-17A/F, a cytokine that is associated with multiple other autoimmune diseases. Inclusion of 12 biomarkers improved the 10-year prediction of a diabetes diagnosis (i.e. the area under the receiver operating curve increased from 0.79 to 0.84), compared with clinical information and plasma glucose alone.

CONCLUSIONS/INTERPRETATION

Systemic molecular changes manifest in plasma several years before a diabetes diagnosis. A particular subset of biomarkers shows distinct, time-dependent patterns, offering potential as predictive markers for diabetes onset. Notably, these biomarkers show shared and distinct patterns between type 1 diabetes and type 2 diabetes. After independent replication, our findings may be used to develop new clinical prediction models.

Targeting Macrophages: Therapeutic Approaches in Diabetic Kidney Disease

Diabetes is not solely a metabolic disorder but also involves inflammatory processes. The immune response it incites is a primary contributor to damage in target organs. Research indicates that during the initial phases of diabetic nephropathy, macrophages infiltrate the kidneys alongside lymphocytes, initiating a cascade of inflammatory reactions. The interplay between macrophages and other renal cells is pivotal in the advancement of kidney disease within a hyperglycemic milieu. While M1 macrophages react to the inflammatory stimuli induced by elevated glucose levels early in the disease progression, their subsequent transition to M2 macrophages, which possess anti-inflammatory and tissue repair properties, also contributes to fibrosis in the later stages of nephropathy by transforming into myofibroblasts. Comprehending the diverse functions of macrophages in diabetic kidney disease and regulating their activity could offer therapeutic benefits for managing this condition.

The Role of the Endocrine System in the Regulation of Acid-Base Balance by the Kidney and the Progression of Chronic Kidney Disease

Systemic acid-base status is primarily determined by the interplay of net acid production (NEAP) arising from metabolism of ingested food stuffs, buffering of NEAP in tissues, generation of bicarbonate by the kidney, and capture of any bicarbonate filtered by the kidney. In chronic kidney disease (CKD), acid retention may occur when dietary acid production is not balanced by bicarbonate generation by the diseased kidney. Hormones including aldosterone, angiotensin II, endothelin, PTH, glucocorticoids, insulin, thyroid hormone, and growth hormone can affect acid-base balance in different ways. The levels of some hormones such as aldosterone, angiotensin II and endothelin are increased with acid accumulation and contribute to an adaptive increase in renal acid excretion and bicarbonate generation. However, the persistent elevated levels of these hormones can damage the kidney and accelerate progression of CKD. Measures to slow the progression of CKD have included administration of medications which inhibit the production or action of deleterious hormones. However, since metabolic acidosis accompanying CKD stimulates the secretion of several of these hormones, treatment of CKD should also include administration of base to correct the metabolic acidosis.

Growth hormone induces transforming growth factor-β1 in podocytes: Implications in podocytopathy and proteinuria

Pituitary growth hormone (GH) is essential for growth, metabolism, and renal function. Overactive GH signaling is associated with impaired kidney function. Glomerular podocytes, a key kidney cell type, play an indispensable role in the renal filtration and express GH receptors (GHR), suggesting the direct action of GH on these cells. However, the precise mechanism and the downstream signaling events by which GH leads to diabetic nephropathy remain to be elucidated. Here we performed proteome analysis of the condition media from human podocytes and confirmed that GH-induces TGF-β1. Inhibition of GH/GHR stimulated-JAK2 signaling abrogates GH-induced TGF-β1 secretion. Mice administered with GH showed glomerular manifestations concomitant with proteinuria. Pharmacological inhibition of TGF-βR1 in mice prevented GH-induced TGF-β dependent SMAD signaling and proteinuria. Conditional deletion of GHR in podocytes protected mice from streptozotocin-induced diabetic nephropathy. GH and TGF-β1 signaling components expression was elevated in the kidneys of human diabetic nephropathy patients. Our study identifies that GH induces TGF-β1 in podocytes, contributing to diabetic nephropathy.

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.

Targeting Insulin-Like Growth Factor-I in Management of Neurological Disorders

The degradation of neurons marks as the pathological reason for onset of most of the neurological diseases although the functional deficiencies and symptoms may vary. Insulin-like growth factor-I (IGF-I) boosts regeneration of both motor and sensory neurons and thus presents as a potential treatment in management of neurological disorders. IGF-I is a pleiotropic agent which stimulates the survival and outgrowth of neurons accompanied by their motility as well as myelination by glial cells. This hormone has been found to possess neuroprotective properties which is in association with its antioxidant and mitochondrial protection activity. Studying and exploring the signaling pathways which mediate pleotropic responses intracellularly have elucidated significant therapeutic approach in treatment and management of neurological disorders by IGF-I. The current review highlights the role of IGF-I in management of major neurological disorders such as depression, Parkinson's disease, and Alzheimer's disease and also covers the mechanisms involved in the process.

Renal effects of growth hormone in health and in kidney disease

Growth hormone (GH) and its mediator insulin-like growth factor-1 (IGF-1) have manifold effects on the kidneys. GH and IGF receptors are abundantly expressed in the kidney, including the glomerular and tubular cells. GH can act either directly on the kidneys or via circulating or paracrine-synthesized IGF-1. The GH/IGF-1 system regulates glomerular hemodynamics, renal gluconeogenesis, tubular sodium and water, phosphate, and calcium handling, as well as renal synthesis of 1,25 (OH)2 vitamin D3 and the antiaging hormone Klotho. The latter also acts as a coreceptor of the phosphaturic hormone fibroblast-growth factor 23 in the proximal tubule. Recombinant human GH (rhGH) is widely used in the treatment of short stature in children, including those with chronic kidney disease (CKD). Animal studies and observations in acromegalic patients demonstrate that GH-excess can have deleterious effects on kidney health, including glomerular hyperfiltration, renal hypertrophy, and glomerulosclerosis. In addition, elevated GH in patients with poorly controlled type 1 diabetes mellitus was thought to induce podocyte injury and thereby contribute to the development of diabetic nephropathy. This manuscript gives an overview of the physiological actions of GH/IGF-1 on the kidneys and the multiple alterations of the GH/IGF-1 system and its consequences in patients with acromegaly, CKD, nephrotic syndrome, and type 1 diabetes mellitus. Finally, the impact of short- and long-term treatment with rhGH/rhIGF-1 on kidney function in patients with kidney diseases will be discussed.

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.

Glomerular filtration rate, blood pressure and microalbuminuria in adults born SGA: A 5-year longitudinal study after cessation of GH treatment

BACKGROUND

Growth hormone treatment increases glomerular filtration rate (GFR), as serum IGF-I stimulates the renin-angiotensin system. Infants born with a low birth weight have a smaller number of nephrons, which cause a lower GFR, a higher blood pressure and a higher albumin-to-creatinine ratio in early adulthood.

METHOD

A total of 261 young adults born SGA, previously treated with growth hormone (SGA-GH), were longitudinally followed. Glomerular filtration rate, based on serum creatinine levels, was determined at cessation of GH treatment and at 6 months, 2 years and 5 years thereafter. Glomerular filtration rate, blood pressure and urinary albumin-to-creatinine ratio at 5 years after cessation of GH were compared with untreated age-matched controls (56 untreated short subjects born SGA [SGA-S], 118 subjects born SGA with spontaneous catch-up growth [SGA-CU], 135 subjects born appropriate for gestational age [AGA]).

RESULTS

Glomerular filtration rate decreased significantly only during the first 6 months after cessation of GH treatment, while remaining well within the normal range (124.6 vs 120.2 mL/min/1.73 m² , P < .001). SGA-GH adults had a similar GFR, blood pressure and urinary albumin-to-creatinine ratio as the healthy controls born SGA and AGA.

CONCLUSION

In conclusion, our 5 years longitudinal follow-up study shows a decrease in GFR during 6 months after GH cessation, but thereafter GFR remained stable and within the normal range. Glomerular filtration rate, blood pressure and urinary albumin-to-creatinine ratio at 21 years of age were similar in GH-treated young adults born SGA and untreated controls born SGA or AGA. We conclude that long-term GH treatment in children born SGA has no unfavourable effects on kidney function in early adulthood. PRÉCIS: We present a longitudinal study on kidney function in the follow-up of growth hormone-treated young adults who were born small for gestational age.

A review of renal GH/IGF1 family gene expression in chronic kidney diseases

Despite decades of study on the contribution of growth hormone (GH) to the development of kidney disease, there remains the question of the relative contribution of elevated levels of GH to kidney damage in humans, particularly in diabetic nephropathy occurring in type 1 patients. In this study, we reviewed several publicly available datasets to examine transcription of twelve genes associated with the GH/IGF1 axis in several types of human and rodent kidney diseases. Our analyses revealed downregulation of renal GHR and IGF1 gene expression in several different chronic human kidney diseases, including diabetic nephropathy, with general upregulation of IGFBP6 in the same tissues and diseases. These findings were generally supported by a review of studies in rodent models. In healthy and diseased human kidneys, increased GHR gene expression was associated with increases in glomerular filtration rate (GFR) and decreases in serum creatinine. IGFBP6 gene expression demonstrated the opposite clinical correlation. Our results suggest the kidney may exhibit GH insensitivity due to low GHR gene expression during most chronic kidney diseases.

The effects of growth hormone on therapy resistance in cancer

Pituitary derived and peripherally produced growth hormone (GH) is a crucial mediator of longitudinal growth, organ development, metabolic regulation with tissue specific, sex specific, and age-dependent effects. GH and its cognate receptor (GHR) are expressed in several forms of cancer and have been validated as an anti-cancer target through a large body of in vitro, in vivo and epidemiological analyses. However, the underlying molecular mechanisms of GH action in cancer prognosis and therapeutic response had been sparse until recently. This review assimilates the critical details of GH-GHR mediated therapy resistance across different cancer types, distilling the therapeutic implications based on our current understanding of these effects.

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.

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.

Mitochondrial dysfunction in diabetic kidney disease

Although diabetic kidney disease (DKD) is the most common cause of end-stage kidney disease worldwide, the pathogenic mechanisms are poorly understood. There is increasing evidence that mitochondrial dysfunction contributes to the development and progression of DKD. Because the kidney is the organ with the second highest oxygen consumption in our body, it is distinctly sensitive to mitochondrial dysfunction. Mitochondrial dysfunction contributes to the progression of chronic kidney disease irrespective of underlying cause. More importantly, high plasma glucose directly damages renal tubular cells, resulting in a wide range of metabolic and cellular dysfunction. Overproduction of reactive oxygen species (ROS), activation of apoptotic pathway, and defective mitophagy are interlinked mechanisms that play pivotal roles in the progression of DKD. Although renal tubular cells have the highest mitochondrial content, podocytes, mesangial cells, and glomerular endothelial cells may all be affected by diabetes-induced mitochondrial injury. Urinary mitochondrial DNA (mtDNA) is readily detectable and may serve as a marker of mitochondrial damage in DKD. Unfortunately, pharmacologic modulation of mitochondrial dysfunction for the treatment of DKD is still in its infancy. Nonetheless, understanding the pathobiology of mitochondrial dysfunction in DKD would facilitate the development of novel therapeutic strategies.

Regulation of PTEN/AKT/FAK pathways by PPARγ impacts on fibrosis in diabetic nephropathy

Renal tubular epithelial-to-mesenchymal transition (EMT) and tubulointerstitial fibrosis (TIF) are important pathological features of diabetic nephropathy (DN). However, the regulatory mechanism underlying EMT and TIF are still unclear. Previous studies showed that the decrease in the expression of phosphatase and tensin homolog deleted on chromosome 10 (PTEN) was closely related to the aggravation of DN, but no published study showed how PTEN participated in the regulation of EMT and TIF. In this study, the rat proximal tubular epithelial cells (NRK52E) and C57BL mice and human kidney tissues were used as the research objects to investigate the mechanism underlying the regulatory effect of peroxisome proliferator-activated receptors γ (PPARγ) on PTEN and its influence on EMT and TIF, the regulation of PTEN's dual activity of lipid phosphatase/protein phosphatase by the serine threonine protein kinase B(AKT)/focal adhesion kinase (FAK) signaling pathway, and the role of PTEN in EMT and TIF. The results showed that PPARγ regulated the expression of PTEN at a transcriptional level and further regulated EMT and TIF. This dual activity could regulate the phosphorylation level of AKT and FAK and also affect FAK transcription. However, the 129 mutant of PTEN (PTEN-G129E) lost the lipid phosphatase activity, and its protein phosphatase activity was involved only in EMT and renal fibrosis through regulating FAK phosphorylation. This study systematically elucidated the role of PPARγ/PTEN/AKT/FAK signaling pathway in EMT and TIF during the pathogenesis of DN.

Abrogation of GH action in Kupffer cells results in increased hepatic CD36 expression and exaggerated nonalcoholic fatty liver disease

OBJECTIVE

To investigate the effects of GH signaling on Kupffer cells and the resulting changes in lipid homeostasis and their underlying mechanism(s) in the livers of diet-induced obese (DIO) mice.

DESIGN

Male macrophage specific-growth hormone receptor knockout mice (MacGHR KO) and their litter mate controls were fed a high fat diet containing 60% calories from fat for 26 weeks. Lipid content and lipid profiles in the liver and circulation were analyzed. Expression levels of CD36 in the liver were quantified by RT-PCR and Western Blot.

RESULTS

Increased hepatic lipid content and abundance of long-chain unsaturated fatty acids were observed in the liver of MacGHR KO mice. These findings were associated with increased steady state levels of CD36 mRNA and protein in MacGHR KO mice when compared with their litter mate controls.

CONCLUSION

GH action in Kupffer cells is required for maintaining hepatic lipid homeostasis, in part via regulation of hepatic CD36 expression.

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.

Association of microalbuminuria with diabetes is stronger in people with prehypertension compared to those with ideal blood pressure

AIM

Microalbuminuria (MA) has been demonstrated as a biomarker for microvascular dysfunction. This study is aimed to evaluate the association of glycaemic status with MA in prehypertensive and ideal BP subjects and to evaluate the interaction between glycaemic and blood pressure status as risk factors for MA prevalence.

METHODS

1059 subjects aged 40-70 with non-hypertension who were recruited from six districts of Tianjin were divided into a prehypertensive group (622 cases) and an ideal blood BP group (437 cases). Subjects of the prehypertensive group and the ideal BP group were divided respectively into three subgroups: normoglycaemia subgroup, prediabetes subgroup and diabetes subgroup. The prevalence of MA in the above three subgroups of subjects with prehypertension and ideal BP were assessed. We performed a statistical analysis for interaction test between glycaemia and BP status on microalbuminuria in the overall study sample by a multivariate logistic regression model. The association of glycaemic status (defined as normoglycaemia, prediabetes, and diabetes) with MA was evaluated separately in prehypertensive and ideal BP subjects.

RESULTS

Results showed that the prevalence of MA in both prehypertensive and ideal BP groups rose with the increasing of classification of glycaemic level of subgroups (32.6%, 18.3%, 14.8% vs. 23.1%, 16.2%, 13.4%), the differences in prehypertensive group were statistically significant (Pearson χ² = 15.24, P < 0.001). The ORs (95% CI) of MA were 1.25 (0.86-1.83) for prediabetes and 2.56 (1.62-4.03) for diabetes in the fully adjusted model. There was no interaction between prediabetes and BP status regarding MA (P = 0.237) but we found a significant interaction between diabetes and BP status (P < 0.001). In the prehypertensive group, multivariate logistic regression models showed that the diabetes subgroup had a significant association with MA, and the adjusted odds ratio of the diabetes subgroup to the normoglycaemia subgroup was 2.68 (95%CI 1.54-4.67) (P < 0.001). However, there was no significant association of glycaemic status with MA in the ideal BP group. Stratified analysis by a multivariate logistic regression model in the whole study population showed that people with both prehypertension and diabetes had the highest risk of MA (adjusted OR = 2.50, 95%CI 1.16-5.36; P = 0.019), compared with those with ideal BP and normoglycaemia (reference group).

CONCLUSIONS

Our findings suggest that there was a statistically significant association between diabetes and microalbuminuria only in prehypertensive subjects. In addition, our study highlights the interaction between prehypertension and diabetes as a risk factor for MA.

Growth hormone (GH)-transgenic insulin-like growth factor 1 (IGF1)-deficient mice allow dissociation of excess GH and IGF1 effects on glomerular and tubular growth

Growth hormone (GH)‐transgenic mice with permanently elevated systemic levels of GH and insulin‐like growth factor 1 (IGF1) reproducibly develop renal and glomerular hypertrophy and subsequent progressive glomerulosclerosis, finally leading to terminal renal failure. To dissociate IGF1‐dependent and ‐independent effects of GH excess on renal growth and lesion development in vivo, the kidneys of 75 days old IGF1‐deficient (I^−/−) and of IGF1‐deficient GH‐transgenic mice (I^−/−/G), as well as of GH‐transgenic (G) and nontransgenic wild‐type control mice (I^+/+) were examined by quantitative stereological and functional analyses. Both G and I^−/−/G mice developed glomerular hypertrophy, hyperplasia of glomerular mesangial and endothelial cells, podocyte hypertrophy and foot process effacement, albuminuria, and glomerulosclerosis. However, I^−/−/G mice exhibited less severe glomerular alterations, as compared to G mice. Compared to I^+/+ mice, G mice exhibited renal hypertrophy with a significant increase in the number without a change in the size of proximal tubular epithelial (PTE) cells. In contrast, I^−/−/G mice did not display significant PTE cell hyperplasia, as compared to I^−/− mice. These findings indicate that GH excess stimulates glomerular growth and induces lesions progressing to glomerulosclerosis in the absence of IGF1. In contrast, IGF1 represents an important mediator of GH‐dependent proximal tubular growth in GH‐transgenic mice.

Notoginsenoside R1 ameliorates podocyte injury in rats with diabetic nephropathy by activating the PI3K/Akt signaling pathway

The present study was designed to examine the protective effect of notoginsenoside R1 (NR1) on podocytes in a rat model of streptozotocin (STZ)-induced diabetic nephropathy (DN), and to explore the mechanism responsible for NR1-induced renal protection. Diabetes was induced by a single injection of STZ, and NR1 was administered daily at a dose of 5 mg/kg (low dose), 10 mg/kg (medium) and 20 mg/kg (high) for 16 weeks in Sprague-Dawley rats. Blood glucose levels, body weight and proteinuria were measured every 4 weeks, starting on the day that the rats received NR1. Furthermore, on the day of sacrifice, blood, urine and kidneys were collected in order to assess renal function according to general parameters. Pathological staining was performed to evaluate the renal protective effect of NR1, and the expression of the key slit diaphragm proteins, namely neprhin, podocin and desmin, were evaluated. In addition, the serum levels of inflammatory cytokines [tumor necrosis factor-α (TNF-α), tumor growth factor-β1 (TGF-β1), interleukin (IL)-1 and IL-6] as well as an anti-inflammatory cytokine (IL-10) were assessed, and the apoptosis of podocytes was quantified. Finally, the phosphoinositide 3-kinase (PI3K)/Akt signaling pathway and the involvement of nuclear factor-κB (NF-κB) inactivation was further analyzed. In this study, NR1 improved renal function by ameliorating histological alterations, increasing the expression of nephrin and podocin, decreasing the expression of desmin, and inhibiting both the inflammatory response as well as the apoptosis of podocytes. Furthermore, NR1 treatment increased the phosphorylation of both PI3K (p85) and Akt, indicating that activation of the PI3K/Akt signaling pathway was involved. Moreover, NR1 treatment decreased the phosphorylation of NF-κB (p65), suggesting the downregulation of NF-κB. This is the first study to the best of our knowledge, to clearly demonstrate that NR1 treatment ameliorates podocyte injury by inhibiting both inflammation and apoptosis through the PI3K/Akt signaling pathway.

Elevated expression levels of serum insulin-like growth factor-1, tumor necrosis factor-α and vascular endothelial growth factor 165 might exacerbate type 2 diabetic nephropathy

AIMS/INTRODUCTION

The present study aimed to determine the associations between expressions of insulin-like growth factor-1 (IGF-1), tumor necrosis factor-α (TNF-α) and vascular endothelial growth factor 165 (VEGF₁₆₅ ) in serum, and occurrence and development of type 2 diabetic nephropathy (DN).

MATERIALS AND METHODS

A total of 108 patients diagnosed as DN were randomly selected, including 50 patients in the microalbuminuria group, 44 patients in the macroalbuminuria group and 14 patients in the renal insufficiency group. Meanwhile, 97 healthy people were collected as a normal control group. Urinary albumin (UALB) and urine creatinine (Cr) of all participants were measured for 24 h, with their ratio (UALB/Cr) being calculated. Enzyme-linked immunosorbent assay was used to detect the serum concentrations of IGF-1, TNF-α and VEGF₁₆₅ .

RESULTS

The expressions of serum IGF-1, TNF-α and VEGF₁₆₅ in the type 2 DN patients were significantly higher than those in the control group (all P < 0.05). The expressions of serum IGF-1, TNF-α and VEGF₁₆₅ in the type 2 DN patients were positively correlated with UALB/Cr (all P < 0.05). As type 2 DN worsened, the expressions of serum IGF-1, TNF-α and VEGF₁₆₅ increased, and type 2 DN severity had positive correlations with serum IGF-1, TNF-α and VEGF₁₆₅ concentrations (all P < 0.05). There was a positive association between IGF-1 and TNF-α, IGF-1 and VEGF₁₆₅ , and TNF-α and VEGF₁₆₅ (all P < 0.05). Logistic regression analysis showed that IGF-1 and VEGF₁₆₅ were associated with the progression of DN (both P < 0.05).

CONCLUSIONS

Elevated expression levels of serum IGF-1, TNF-α and VEGF₁₆₅ might exacerbate type 2 DN.

In silico Structural characterization of podocin and assessment of nephrotic syndrome-associated podocin mutants

Nephrotic syndrome (NS) is manifested by hyperproteinuria, hypoalbuminemia, and edema. NPHS2 that encodes podocin was found to have most mutations among the genes that are involved in the pathophysiology of NS. Podocin, an integral membrane protein belonging to stomatin family, is expressed exclusively in podocytes and is localized to slit-diaphragm (SD). Mutations in podocin are known to be associated with steroid-resistant NS and rapid progression to end-stage renal disease, thus signifying its role in maintaining SD integrity and podocyte function. The structural insights of podocin are not known, and the precise mechanism by which podocin contributes to the architecture of SD is yet to be elucidated. In this study, we deduced a model for human podocin, discussed the details of transmembrane localization and intrinsically unstructured regions, and provide an understanding of how podocin interacts with other SD components. Intraprotein interactions were assessed in wild-type podocin and in some of its mutants that are associated with idiopathic NS. Mutations in podocin alter the innate intraprotein interactions affecting the native structure of podocin and its ability to form critical complex with subpodocyte proteins. © 2016 IUBMB Life, 68(7):578-588, 2016.

The role of IL-18 in type 1 diabetic nephropathy: The problem and future treatment

Diabetic vascular complication is a leading cause of diabetic nephropathy, a progressive increase in urinary albumin excretion coupled with elevated blood pressure leading to declined glomerular filtration and eventually end stage renal failure. There is growing evidence that activated inflammation is contributing factor to the pathogenesis of diabetic nephropathy. Meanwhile, IL-18, a member of the IL-1 family of inflammatory cytokines, is involved in the development and progression of diabetic nephropathy. However, the benefits derived from the current therapeutics for diabetic nephropathy strategies still provide imperfect protection against renal progression. This imperfection points to the need for newer therapeutic agents that have potential to affect primary mechanisms contributing to the pathogenesis of diabetic nephropathy. Therefore, the recognition of IL-18 as significant pathogenic mediators in diabetic nephropathy leaves open the possibility of new potential therapeutic targets.

Hydrochloride pioglitazone protects diabetic rats against podocyte injury through preserving glomerular podocalyxin expression

OBJECTIVE

We sought to test the effect of different dosages of pioglitazone (PIO) on the glomerular expression of podocalyxin and urinary sediment podocalyxin excretion and to explore the potential renoprotective mechanism.

MATERIALS AND METHODS

Type 1 diabetes induced with streptozotocin (65 mg/kg) in 36 male Sprague-Dawley rats were randomly allocated to be treated with vehicle or 10, 20, 30 mg/kg/d PIO respectively for 8 weeks. Eight rats were enrolled in the normal control group.

RESULTS

At 8th week, rats were sacrificed for the observation of kidney injury through electron microscope. Glomerular podocalyxin production including mRNA and protein were determined by RT-PCR and immunohistochemistry respectively. Levels of urinary albumin excretion and urinary sediment podocalyxin, kidney injury index were all significantly increased, whereas expression of glomerular podocalyxin protein and mRNA were decreased significantly in diabetic rats compared to normal control. Dosages-dependent analysis revealed that protective effect of PIO ameliorated the physiopathological changes and reached a peak at dosage of 20 mg/kg/d.

CONCLUSION

PIO could alleviate diabetic kidney injury in a dose-dependent pattern and the role may be associated with restraining urinary sediment podocalyxin excretion and preserving the glomerular podocalyxin expression.

Male bovine GH transgenic mice have decreased adiposity with an adipose depot-specific increase in immune cell populations

White adipose tissue (WAT) is composed of mature adipocytes and a stromal vascular fraction (SVF), which contains a variety of cells, including immune cells that vary among the different WAT depots. Growth hormone (GH) impacts immune function and adiposity in an adipose depot-specific manner. However, its effects on WAT immune cell populations remain unstudied. Bovine GH transgenic (bGH) mice are commonly used to study the in vivo effects of GH. These giant mice have an excess of GH action, impaired glucose metabolism, decreased adiposity, increased lean mass, and a shortened lifespan. Therefore, the purpose of this study was to characterize the WAT depot-specific differences in immune cell populations in the presence of excess GH in vivo. Three WAT depots were assessed: inguinal (sc), epididymal (EPI), and mesenteric (MES). Subcutaneous and MES bGH WAT depots showed a significantly higher number of total SVF cells, yet only MES bGH WAT had higher leukocyte counts compared with control samples. By means of flow cytometry analysis of the SVF, we detected greater macrophage and regulatory T-cell infiltration in sc and MES bGH WAT depots compared with controls. However, no differences were observed in the EPI WAT depot. RNA-sequencing confirmed significant alterations in pathways related to T-cell infiltration and activation in the sc depot with fewer significant changes in the EPI bGH WAT depot. These findings collectively point to a previously unrecognized role for GH in influencing the distribution of WAT immune cell populations in a depot-specific manner.

Glomerular endothelial cell injury and cross talk in diabetic kidney disease

Diabetic kidney disease (DKD) remains a leading cause of new-onset end-stage renal disease (ESRD), and yet, at present, the treatment is still very limited. A better understanding of the pathogenesis of DKD is therefore necessary to develop more effective therapies. Increasing evidence suggests that glomerular endothelial cell (GEC) injury plays a major role in the development and progression of DKD. Alteration of the glomerular endothelial cell surface layer, including its major component, glycocalyx, is a leading cause of microalbuminuria observed in early DKD. Many studies suggest a presence of cross talk between glomerular cells, such as between GEC and mesangial cells or GEC and podocytes. PDGFB/PDGFRβ is a major mediator for GEC and mesangial cell cross talk, while vascular endothelial growth factor (VEGF), angiopoietins, and endothelin-1 are the major mediators for GEC and podocyte communication. In DKD, GEC injury may lead to podocyte damage, while podocyte loss further exacerbates GEC injury, forming a vicious cycle. Therefore, GEC injury may predispose to albuminuria in diabetes either directly or indirectly by communication with neighboring podocytes and mesangial cells via secreted mediators. Identification of novel mediators of glomerular cell cross talk, such as microRNAs, will lead to a better understanding of the pathogenesis of DKD. Targeting these mediators may be a novel approach to develop more effective therapy for DKD.

Genetic dissection of IGF1-dependent and -independent effects of permanent GH excess on postnatal growth and organ pathology of mice

To study insulin-like growth factor 1 (IGF1)-independent effects of permanent growth hormone (GH) excess on body and organ growth and pathology in vivo, hemizygous bovine GH transgenic mice with homozygous disruption of the Igf1 gene (Igf1(-/-)/GH) were generated, and examined in comparison to Igf1(-/-), Igf1(+/-), wild-type (WT), Igf1(+/-)/GH, and GH mice. GH mice and Igf1(+/-)/GH mice showed increased serum IGF1 levels and the well-known giant-phenotype of GH transgenic mice. In contrast, the typical dwarf-phenotype of Igf1(-/-) mice was only slightly ameliorated in Igf1(-/-)/GH mice. Similar to GH mice, Igf1(-/-)/GH mice displayed hepatocellular hypertrophy, glomerulosclerosis, and reduced volumes of acidophilic cells in the pituitary gland. However, GH excess associated skin lesions of male GH mice were not observed in Igf1(-/-)/GH mice. Therefore, development of GH excess induced liver-, kidney-, and pituitary gland-alterations in GH transgenic mice is independent of IGF1 whereas GH stimulated body growth depends on IGF1.

Evaluation of growth hormone (GH) action in mice: discovery of GH receptor antagonists and clinical indications

The discovery of a growth hormone receptor antagonist (GHA) was initially established via expression of mutated GH genes in transgenic mice. Following this discovery, development of the compound resulted in a drug termed pegvisomant, which has been approved for use in patients with acromegaly. Pegvisomant treatment in a dose dependent manner results in normalization of IGF-1 levels in most patients. Thus, it is a very efficacious and safe drug. Since the GH/IGF-1 axis has been implicated in the progression of several types of cancers, many have suggested the use of pegvisomant as an anti-cancer therapeutic. In this manuscript, we will review the use of mouse strains that possess elevated or depressed levels of GH action for unraveling many of GH actions. Additionally, we will describe experiments in which the GHA was discovered, review results of pegvisomant's preclinical and clinical trials, and provide data suggesting pegvisomant's therapeutic value in selected types of cancer.

Molecular and cellular events mediating glomerular podocyte dysfunction and depletion in diabetes mellitus

The essential function of the kidney is to ensure formation of a relatively protein-free ultra-filtrate, urine. The rate of filtration and composition of the primary renal filtrate is determined by the transport of fluid and solutes across the glomerular filtration barrier consisting of endothelial cells, the glomerular basement membrane, and podocyte foot processes. In diabetes mellitus (DM), components of the kidney that enable renal filtration get structurally altered and functionally compromised resulting in proteinuria that often progresses to end-stage renal disease. Histological alterations in DM include early hypertrophy of glomerular and tubular components, subsequent thickening of basement membrane in glomeruli and tubules, progressive accumulation of extracellular matrix proteins in the glomerular mesangium and loss of podocytes, together constituting a clinical condition referred to as diabetic nephropathy (DN). The glomerulus has become the focus of research investigating the mechanism of proteinuria. In particular, the progressive dysfunction and/or loss of podocytes that is contemporaneous with proteinuria in DN have attracted intense scientific attention. The absolute number of podocytes predicts glomerular function and podocyte injury is a hallmark of various glomerular diseases. This review discusses the importance of podocytes in normal renal filtration and details the molecular and cellular events that lead to podocyte dysfunction and decreased podocyte count in DN.

Metabolic syndrome and associated chronic kidney diseases: nutritional interventions

Lifestyle changes such as dietary habits, sedentary life and consumption of energy-dense foods that have occurred over the years has led to an epidemic of abdominal obesity, which in turn resulted in dramatic increase in the prevalence of metabolic syndrome (MetS). Different expert panels have provided various definitions for MetS to enable a clinical diagnosis and treatment of patients at risk of associated complications. Obesity and obesity mediated MetS has been paralleled by escalation in the incidence of chronic kidney disease (CKD). A better understanding of the pathophysiology of MetS and identification of individuals with MetS early in the life course could be important for initiating interventions such as lifestyle modification and dietary restrictions that form the basis for prevention and treatment of MetS and related co-morbidities including CKD. This review is intended to provide a comprehensive summary of the evolution of definition of MetS and association of MetS with CKD. In particular, mechanism of obesity and diabetes mediated CKD and emerging dietary therapies for MetS associated CKD will be discussed.

Human conditions of insulin-like growth factor-I (IGF-I) deficiency

Insulin-like growth factor I (IGF-I) is a polypeptide hormone produced mainly by the liver in response to the endocrine GH stimulus, but it is also secreted by multiple tissues for autocrine/paracrine purposes. IGF-I is partly responsible for systemic GH activities although it possesses a wide number of own properties (anabolic, antioxidant, anti-inflammatory and cytoprotective actions). IGF-I is a closely regulated hormone. Consequently, its logical therapeutical applications seems to be limited to restore physiological circulating levels in order to recover the clinical consequences of IGF-I deficiency, conditions where, despite continuous discrepancies, IGF-I treatment has never been related to oncogenesis. Currently the best characterized conditions of IGF-I deficiency are Laron Syndrome, in children; liver cirrhosis, in adults; aging including age-related-cardiovascular and neurological diseases; and more recently, intrauterine growth restriction. The aim of this review is to summarize the increasing list of roles of IGF-I, both in physiological and pathological conditions, underlying that its potential therapeutical options seem to be limited to those proven states of local or systemic IGF-I deficiency as a replacement treatment, rather than increasing its level upper the normal range.

Divergent roles of Smad3 and PI3-kinase in murine adriamycin nephropathy indicate distinct mechanisms of proteinuria and fibrogenesis

Multiple transforming growth factor (TGF)-β-induced fibrogenic signals have been described in vitro. To evaluate mechanisms in vivo, we used an adriamycin nephropathy model in 129x1/Svj mice that display massive proteinuria by days 5 to 7 and pathological findings similar to human focal segmental glomerulosclerosis by day 14. TGF-β mRNA expression increased after day 7 along with nuclear translocation of the TGF-β receptor-specific transcription factor Smad3. Inhibiting TGF-β prevented both pathological changes and type-I collagen and fibronectin mRNA expression, but proteinuria persisted. Renal Akt was phosphorylated in adriamycin-treated mice, suggesting PI3-kinase activation. Expression of mRNA for the p110γ isozyme of PI3-kinase was specifically increased and p110γ colocalized with nephrin by immunohistochemistry early in disease. Nephrin levels subsequently decreased. Inhibition of p110γ by AS605240 preserved nephrin expression and prevented proteinuria. In cultured podocytes, adriamycin stimulated p110γ expression. AS605240, but not a TGF-β receptor kinase inhibitor, prevented adriamycin-induced cytoskeletal disorganization and apoptosis, supporting a role for p110γ in podocyte injury. AS605240, at a dose that decreased proteinuria, prevented renal collagen mRNA expression in vivo but did not affect TGF-β-stimulated collagen induction in vitro. Thus, PI3-kinase p110γ mediates initial podocyte injury and proteinuria, both of which precede TGF-β-mediated glomerular scarring.

The insulin-like growth factor system in kidney disease and hypertension

PURPOSE OF REVIEW

The insulin-like growth factor system plays an important role in renal physiology and it is perturbed in a range of kidney diseases.

RECENT FINDINGS

Some insulin-like growth factor (IGF) actions in the kidney are mediated by nitric oxide. Growth hormone and IGF-binding proteins may contribute to renal diseases via effects on podocytes and proximal tubule cells. In contrast, growth hormone and IGF-I may counteract the catabolic consequences of end-stage renal disease. Polymorphisms in the IGF system are associated with hypertension.

SUMMARY

Further studies are needed to determine whether modulating the IGF system may have a role in treating kidney diseases and/or hypertension.