Systemic and renal growth hormone-IGF1 axis involvement in a mouse model of type 2 diabetes

Co-differential genes between DKD and aging: implications for a diagnostic model of DKD

Objective

Diabetic kidney disease (DKD) is a serious complication of diabetes mellitus (DM) that is closely related to aging. In this study, we found co-differential genes between DKD and aging and established a diagnostic model of DKD based on these genes.

Methods

Differentially expressed genes (DEGs) in DKD were screened using GEO datasets. The intersection of the DEGs of DKD and aging-related genes revealed DKD and aging co-differential genes. Based on this, a genetic diagnostic model for DKD was constructed using LASSO regression. The characteristics of these genes were investigated using consensus clustering, WGCNA, functional enrichment, and immune cell infiltration. Finally, the expression of diagnostic model genes was analyzed using single-cell RNA sequencing (scRNA-seq) in DKD mice (model constructed by streptozotocin (STZ) injection and confirmed by tissue section staining).

Results

First, there were 159 common differential genes between DKD and aging, 15 of which were significant. These co-differential genes were involved in stress, glucolipid metabolism, and immunological functions. Second, a genetic diagnostic model (including IGF1, CETP, PCK1, FOS, and HSPA1A) was developed based on these genes. Validation of these model genes in scRNA-seq data revealed statistically significant variations in FOS, HSPA1A, and PCK1 gene expression between the early DKD and control groups. Validation of these model genes in the kidneys of DKD mice revealed that Igf1, Fos, Pck1, and Hspa1a had lower expression in DKD mice, with Igf1 expression being statistically significant.

Conclusion

Our findings suggest that DKD and aging co-differential genes are significant in DKD diagnosis, providing a theoretical basis for novel research directions on DKD.

IGFBP-1 expression is reduced in human type 2 diabetic glomeruli and modulates β1-integrin/FAK signalling in human podocytes

AIMS/HYPOTHESIS

Podocyte loss or injury is one of the earliest features observed in the pathogenesis of diabetic kidney disease (DKD), which is the leading cause of end-stage renal failure worldwide. Dysfunction in the IGF axis, including in IGF binding proteins (IGFBPs), is associated with DKD, particularly in the early stages of disease progression. The aim of this study was to investigate the potential roles of IGFBPs in the development of type 2 DKD, focusing on podocytes.

METHODS

IGFBP expression was analysed in the Pima DKD cohort, alongside data from the Nephroseq database, and in ex vivo human glomeruli. Conditionally immortalised human podocytes and glomerular endothelial cells were studied in vitro, where IGFBP-1 expression was analysed using quantitative PCR and ELISAs. Cell responses to IGFBPs were investigated using migration, cell survival and adhesion assays; electrical cell-substrate impedance sensing; western blotting; and high-content automated imaging.

RESULTS

Data from the Pima DKD cohort and from the Nephroseq database demonstrated a significant reduction in glomerular IGFBP-1 in the early stages of human type 2 DKD. In the glomerulus, IGFBP-1 was predominantly expressed in podocytes and controlled by phosphoinositide 3-kinase (PI3K)-forkhead box O1 (FoxO1) activity. In vitro, IGFBP-1 signalled to podocytes via β1-integrins, resulting in increased phosphorylation of focal-adhesion kinase (FAK), increasing podocyte motility, adhesion, electrical resistance across the adhesive cell layer and cell viability.

CONCLUSIONS/INTERPRETATION

This work identifies a novel role for IGFBP-1 in the regulation of podocyte function and that the glomerular expression of IGFBP-1 is reduced in the early stages of type 2 DKD, via reduced FoxO1 activity. Thus, we hypothesise that strategies to maintain glomerular IGFBP-1 levels may be beneficial in maintaining podocyte function early in DKD.

IGF-1/IGF-1R blockade ameliorates diabetic kidney disease through normalizing Snail1 expression in a mouse model

This study investigated the role of insulin-like growth factor-1/insulin-like growth factor-1 receptor (IGF-1/IGF-1R) in the genesis and progression of diabetic kidney disease (DKD) in a streptozotocin (STZ)-induced mouse diabetes model. We showed elevated IGF-1 expression in the DKD kidneys after 16 wk of diabetic onset. Intraperitoneal administration of IGF-1R inhibitor (glycogen synthase kinase-3β, GSK4529) from week 8 to week 16 postdiabetes induction ameliorated urinary albumin excretion and kidney histological changes due to diabetes, including amelioration of glomerulomegaly, inflammatory infiltration, and tubulointerstitial fibrosis. The GSK4529 treatment also attenuated alterations in renal tubular expression of E-cad and matrix protein fibronectin. Moreover, renal fibrosis in DKD (without treatment) was associated with Snail1 overexpression that was effectively prevented by IGF-1R inhibition. Further experiments in cultured renal epithelial cells (NRK) showed that IGF-1 silencing reproduced in vivo effects of IGF-1R inhibition with markedly attenuated Snail1 expression and near normalization of the Ecad1 and fibronectin expression pattern. Further Snail1 silencing prevented high-glucose-induced changes without affecting IGF-1 expression, consistent with Snail1 acting downstream to IGF-1. The antifibrotic effects were also shown with benazepril or insulin treatment but to a much lesser degree. In summary, in STZ-induced diabetic mice, activation of IGF-1 in diabetic kidneys induces fibrogenesis through Snail1 upregulation. The diabetes-related histological and functional changes, as well as fibrogenesis, can be attenuated by IGF-1/IGF-1R inhibition.

Klotho protein supplementation reduces blood pressure and renal hypertrophy in db/db mice, a model of type 2 diabetes

AIMS

Klotho interacts with various membrane proteins, such as receptors for transforming growth factor (TGF)-β and insulin-like growth factor (IGF), to alter their function. Renal expression of klotho is diminished in diabetes. The present study examined whether exogenous klotho protein supplementation ameliorates kidney injury and renin-angiotensin system (RAS) in db/db mice.

METHODS

We investigated the effects of klotho supplementation on diabetic kidney injury and RAS. Recombinant human klotho protein (10 μg/kg/d) was administered to db/db mice daily.

RESULTS

Klotho protein supplementation reduced kidney weight, systolic blood pressure (SBP), albuminuria, glomerular filtration rate, and 8-epi-prostaglandin F2α excretion without affecting body weight. Although klotho supplementation did not alter glycated albumin, it reduced renal angiotensin II levels associated with reduced renal expression of angiotensinogen. Klotho supplementation improved renal expression of superoxide dismutase (SOD), and endogenous renal expression of klotho. Klotho supplementation reduced the levels of hypoxia-inducible factor, phosphorylated Akt, and phosphorylated mTOR and decreased the renal expression of TGF-β, tumour necrosis factor (TNF), and fibronectin.

CONCLUSIONS

These data indicate that klotho supplementation reduces blood pressure and albuminuria along with ameliorating renal RAS activation in db/db mice. Furthermore, these results suggest that klotho inhibits IGF signalling, induces SOD expression to reduce oxidative stress, and suppresses Akt-mTOR signalling to inhibit abnormal kidney growth. Collectively, the results suggest that klotho inhibits TGF-β and TNF signalling, resulting in a decline in renal fibrosis.

Uncoupled iron homeostasis in type 2 diabetes mellitus

Diabetes mellitus is frequently associated with iron overload conditions, such as primary and secondary hemochromatosis. Conversely, patients affected by type 2 diabetes mellitus (T2DM) show elevated ferritin levels, a biomarker for increased body iron stores. Despite these documented associations between dysregulated iron metabolism and T2DM, the underlying mechanisms are poorly understood. Here, we show that T2DM patients have reduced serum levels of hepcidin, the iron-regulated hormone that maintains systemic iron homeostasis. Consistent with this finding, we also observed an increase in circulating iron and ferritin levels. Our analysis of db/db mice demonstrates that this model recapitulates the systemic alterations observed in patients. Interestingly, db/db mice show an overall hepatic iron deficiency despite unaltered expression of ferritin and the iron importer TfR1. In addition, the liver correctly senses increased circulating iron levels by activating the BMP/SMAD signaling pathway even though hepcidin expression is decreased. We show that increased AKT phosphorylation may override active BMP/SMAD signaling and decrease hepcidin expression in 10-week old db/db mice. We conclude that the metabolic alterations occurring in T2DM impact on the regulation of iron homeostasis on multiple levels. As a result, metabolic perturbations induce an "iron resistance" phenotype, whereby signals that translate increased circulating iron levels into hepcidin production, are dysregulated.

KEY MESSAGES

T2DM patients show increased circulating iron levels. T2DM is associated with inappropriately low hepcidin levels. Metabolic alterations in T2DM induce an "iron resistance" phenotype.

Role of estrogen receptor signaling in skeletal response to leptin in female ob/ob mice

Leptin, critical in regulation of energy metabolism, is also important for normal bone growth, maturation and turnover. Compared to wild type (WT) mice, bone mass is lower in leptin-deficient ob/ob mice. Osteopenia in growing ob/ob mice is due to decreased bone accrual, and is associated with reduced longitudinal bone growth, impaired cancellous bone maturation and increased marrow adipose tissue (MAT). However, leptin deficiency also results in gonadal dysfunction, disrupting production of gonadal hormones which regulate bone growth and turnover. The present study evaluated the role of increased estrogen in mediating the effects of leptin on bone in ob/ob mice. Three-month-old female ob/ob mice were randomized into one of the 3 groups: (1) ob/ob + vehicle (veh), (2) ob/ob + leptin (leptin) or (3) ob/ob + leptin and the potent estrogen receptor antagonist ICI 182,780 (leptin + ICI). Age-matched WT mice received vehicle. Leptin (40 µg/mouse, daily) and ICI (10 µg/mouse, 2×/week) were administered by subcutaneous injection for 1 month and bone analyzed by X-ray absorptiometry, microcomputed tomography and static and dynamic histomorphometry. Uterine weight did not differ between ob/ob mice and ob/ob mice receiving leptin + ICI, indicating that ICI successfully blocked the uterine response to leptin-induced increases in estrogen levels. Compared to leptin-treated ob/ob mice, ob/ob mice receiving leptin + ICI had lower uterine weight; did not differ in weight loss, MAT or bone formation rate; and had higher longitudinal bone growth rate and cancellous bone volume fraction. We conclude that increased estrogen signaling following leptin treatment is dispensable for the positive actions of leptin on bone and may attenuate leptin-induced bone growth.

Leptin receptor deficient diabetic (db/db) mice are compromised in postnatal bone regeneration

Increased fragility fracture risk with improper healing is a frequent and severe complication of insulin resistance (IR). The mechanisms impairing bone health in IR are still not fully appreciated, which gives importance to studies on bone pathologies in animal models of diabetes. Mice deficient in leptin signaling are widely used models of IR and its comorbidities. Leptin was first recognized as a hormone, regulating appetite and energy balance; however, recent studies have expanded its role showing that leptin is a link between insulin-dependent metabolism and bone homeostasis. In the light of these findings, it is intriguing to consider the role of leptin resistance in bone regeneration. In this study, we show that obese diabetic mice lacking leptin receptor (db/db) are deficient in postnatal regenerative osteogenesis. We apply an ectopic osteogenesis and a fracture healing model, both showing that db/db mice display compromised bone acquisition and regeneration capacity. The underlying mechanisms include delayed periosteal mesenchymatic osteogenesis, premature apoptosis of the cartilage callus and impaired microvascular invasion of the healing tissue. Our study supports the use of the db/db mouse as a model of IR associated bone-healing deficits and can aid further studies of mesenchymatic cell homing and differentiation, microvascular invasion, cartilage to bone transition and callus remodeling in diabetic fracture healing.

Mechanisms of diabetic complications

It is increasingly apparent that not only is a cure for the current worldwide diabetes epidemic required, but also for its major complications, affecting both small and large blood vessels. These complications occur in the majority of individuals with both type 1 and type 2 diabetes. Among the most prevalent microvascular complications are kidney disease, blindness, and amputations, with current therapies only slowing disease progression. Impaired kidney function, exhibited as a reduced glomerular filtration rate, is also a major risk factor for macrovascular complications, such as heart attacks and strokes. There have been a large number of new therapies tested in clinical trials for diabetic complications, with, in general, rather disappointing results. Indeed, it remains to be fully defined as to which pathways in diabetic complications are essentially protective rather than pathological, in terms of their effects on the underlying disease process. Furthermore, seemingly independent pathways are also showing significant interactions with each other to exacerbate pathology. Interestingly, some of these pathways may not only play key roles in complications but also in the development of diabetes per se. This review aims to comprehensively discuss the well validated, as well as putative mechanisms involved in the development of diabetic complications. In addition, new fields of research, which warrant further investigation as potential therapeutic targets of the future, will be highlighted.

Altered gene expression involved in insulin signaling pathway in type II diabetic osteoporosis rats model

It is well established that both estrogen loss and type II diabetes mellitus (DMII) can impair bone metabolism, but whether estrogen loss exacerbates the effects of DMII is unclear. Therefore, we determined if ovariectomy (OVX) of rats on a long-term high-fat/sugar diet and injection of a low dose of streptozotocin (DMII) decreased bone mineral density (BMD) more than OVX or DMII alone. Bone insulin signaling is known to support bone metabolism; therefore, we also tested the hypothesis that OVX DMII rats (DOVX) would exhibit greater reductions in the expression of proteins important in insulin signaling, including IRS-1, IRS-2, and IGF-1. As hypothesized, BMD and plasma estrogen levels were decreased more in DOVX rats than in rats following OVX (NOVX) or DMII (DS) alone. IGF-1 expression was decreased in the liver, kidney, skeletal muscle, and bone of DOVX, DS, and NOVX rats; however, the decrease was larger and occurred sooner in DOVX rats. While IRS-1 and IRS-2 decreased in most groups in all tissues examined, the expression patterns differed in both a group- and tissue-dependent fashion. In conclusion, these data demonstrate that estrogen loss and DMII induced by a high-fat/sugar diet interact to produce osteoporosis and support the hypothesis that the bone loss may be mediated at least in part by concurrent decreases in the insulin signaling proteins in bone.

Impact of growth hormone hypersecretion on the adult human kidney

Acromegaly is most often secondary to a GH-secreting pituitary adenoma with increased Insulin-like Growth Factor type 1 (IGF-1) level. The consequences of GH/IGF-1 hypersecretion reflect the diversity of action of these hormones. The genes of the GH receptor (GHR), IGF-1, IGF-1 receptor (IGF-1R) and IGF-binding proteins (IGF-BP) are physiologically expressed in the adult kidney, suggesting a potential role of the somatotropic axis on renal structure and functions. The expression of these proteins is highly organized and differs according to the anatomical and functional segments of the nephron suggesting different roles of GH and IGF-1 in these segments. In animals, chronic exposure to high doses of GH induces glomerulosclerosis and increases albuminuria. Studies in patients with GH hypersecretion have identified numerous targets of GH/IGF-1 axis on the kidney: 1) an impact on renal filtration with increased glomerular filtration rate (GFR), 2) a structural impact with an increase in kidney weight and glomerular hypertrophy, and 3) a tubular impact leading to hyperphosphatemia, hypercalciuria and antinatriuretic effects. Despite the increased glomerular filtration rate observed in patients with GH hypersecretion, GH is an inefficient treatment for chronic renal failure. GH and IGF-1 seem to be involved in the physiopathology of diabetic nephropathy; this finding offers the possibility of targeting the GH/IGF-1 axis for the prevention and the treatment of diabetic nephropathy.

Metabolic imbalance of the insulin-like growth factor-I axis in Zucker diabetic fatty rats

In healthy conditions, insulin-like growth factor-I (IGF-I) acts in a coordinated fashion with insulin to lower glycemia, mainly by increasing insulin sensitivity in peripheral tissues. The aim of this study was to explore the relationship between glucose homeostasis and the endocrine IGF-I axis in Zucker diabetic fatty (ZDF) rats. The plasma levels of glucose, insulin, growth hormone, free IGF-I, total IGF-I (associated to insulin-like growth factor binding proteins plus free), and corticosterone were measured in 13-week-old ZDF rats and in age-matched controls under fasting and postprandial conditions. The plasma IGF-I binding capacity was measured by radioligand binding. In ZDF rats, fasting total and free IGF-I levels were reduced by 22% and 92%, respectively, compared with controls. Postprandial free IGF-I was reduced by 35%, whereas total IGF-I was unaffected. The plasma IGF-I binding capacity in ZDF rats was reduced by 24% after fasting and by 13% under postprandial conditions. A clear correlation between free IGF-I and insulin was observed in postprandial controls but not in ZDF rats. A principal component analysis clearly separated ZDF and control rats into 2 main components under both fasting and postprandial conditions. The first component was determined equally by total IGF-I, bound IGF-I, the free to total IGF-I ratio, and the IGF-I binding capacity. The second component was determined mostly by glucose and insulin. Our results show a marked alteration of the plasma IGF-I levels and of the capacity of plasma to bind IGF-I, and a disturbed relationship between IGF-I and postprandial insulinemia in a rat model of type 2 diabetes mellitus.

Impaired hypothalamic regulation of endocrine function and delayed counterregulatory response to hypoglycemia in Magel2-null mice

Hypothalamic dysfunction may underlie endocrine abnormalities in Prader-Willi syndrome (PWS), a genetic disorder that features GH deficiency, obesity, and infertility. One of the genes typically inactivated in PWS, MAGEL2, is highly expressed in the hypothalamus. Mice deficient for Magel2 are obese with increased fat mass and decreased lean mass and have blunted circadian rhythm. Here, we demonstrate that Magel2-null mice have abnormalities of hypothalamic endocrine axes that recapitulate phenotypes in PWS. Magel2-null mice had elevated basal corticosterone levels, and although male Magel2-null mice had an intact corticosterone response to restraint and to insulin-induced hypoglycemia, female Magel2-null mice failed to respond to hypoglycemia with increased corticosterone. After insulin-induced hypoglycemia, Magel2-null mice of both sexes became more profoundly hypoglycemic, and female mice were slower to recover euglycemia, suggesting an impaired hypothalamic counterregulatory response. GH insufficiency can produce abnormal body composition, such as that seen in PWS and in Magel2-null mice. Male Magel2-null mice had Igf-I levels similar to control littermates. Female Magel2-null mice had low Igf-I levels and reduced GH release in response to stimulation with ghrelin. Female Magel2-null mice did respond to GHRH, suggesting that their GH deficiency has a hypothalamic rather than pituitary origin. Female Magel2-null mice also had higher serum adiponectin than expected, considering their increased fat mass, and thyroid (T(4)) levels were low. Together, these findings strongly suggest that loss of MAGEL2 contributes to endocrine dysfunction of hypothalamic origin in individuals with PWS.

High-level secretory expression, purification and characterization of Ailuropoda melanoleuca growth hormone in Pichia pastoris

Growth hormone is one of the most important hormones, which is involved in many reproductive processes of giant panda Ailuropoda melanoleuca. In this study, the mature peptide of A. melanoleuca growth hormone (AmGH) was successfully expressed and secreted in Pichia pastoris under the control of AOX1 promoter. The expression condition for AmGH in P. pastoris, such as the expression time, pH value and methanol concentration in the BMMY were optimized and the AmGH expression level is about 100 mg/L using GS115 recombinant under optimized condition (96 h of 1.5% methanol induction). The secreted nascent AmGH were purified using ammonium sulfate fractionation. The mature AmGH protein exhibited a molecular mass of approximately 22 kDa on SDS-PAGE. This study would provide a new opportunity for large-scale expression and purification of AmGH, which might facilitate studies on the biological activity of AmGH.

Role of IGF-I in Type 2 diabetes: a focus on the mouse model

Insulin resistance, the key mechanism in Type 2 diabetes mellitus (T2DM) is also associated with the deregulation of other glucose homeostasis pathways, such as the growth hormone (GH)-IGF-I system. In this review, we summarize the endocrine and renal GH-IGF axis changes in db/db mice, a model of T2DM, and compare it with the nonobese diabetic mouse model of T1DM. In the latter, elevated circulating GH levels (associated with kidney disease) could be ameliorated with the use of GH antagonists. Contrary to that, in the obese db/db mice, serum GH and IGF-I levels are decreased and tissue levels of IGF-binding protein 1 (Igfbp1) are increased. The latter hinted again for the known inverse correlation between insulin and Igfbp1 and was mediated by changes in the transcription factor phosphorylated forkhead box O1 in obese animals. In addition, the decrease in circulating IGF-I and GH levels causes a state of low free and active IGF-I, which may further impair tissue viability (including pancreatic β-cells). Thus, further GH inhibition to modulate complications in T2DM is not indicated, but the therapeutic role of IGF-1 in this disease remains to be determined.