IGF-1-induced lipid accumulation impairs mesangial cell migration and contractile function

Klotho's impact on diabetic nephropathy and its emerging connection to diabetic retinopathy

Diabetic nephropathy (DN) is the leading cause of end-stage renal disease worldwide and is a significant burden on healthcare systems. α-klotho (klotho) is a protein known for its anti-aging properties and has been shown to delay the onset of age-related diseases. Soluble klotho is produced by cleavage of the full-length transmembrane protein by a disintegrin and metalloproteases, and it exerts various physiological effects by circulating throughout the body. In type 2 diabetes and its complications DN, a significant decrease in klotho expression has been observed. This reduction in klotho levels may indicate the progression of DN and suggest that klotho may be involved in multiple pathological mechanisms that contribute to the onset and development of DN. This article examines the potential of soluble klotho as a therapeutic agent for DN, with a focus on its ability to impact multiple pathways. These pathways include anti-inflammatory and oxidative stress, anti-fibrotic, endothelial protection, prevention of vascular calcification, regulation of metabolism, maintenance of calcium and phosphate homeostasis, and regulation of cell fate through modulation of autophagy, apoptosis, and pyroptosis pathways. Diabetic retinopathy shares similar pathological mechanisms with DN, and targeting klotho may offer new insights into the prevention and treatment of both conditions. Finally, this review assesses the potential of various drugs used in clinical practice to modulate klotho levels through different mechanisms and their potential to improve DN by impacting klotho levels.

Renal UTX-PHGDH-serine axis regulates metabolic disorders in the kidney and liver

Global obesity epidemics impacts human health and causes obesity-related illnesses, including the obesity-related kidney and liver diseases. UTX, a histone H3K27 demethylase, plays important roles in development and differentiation. Here we show that kidney-specific knockout Utx inhibits high-fat diet induced lipid accumulation in the kidney and liver via upregulating circulating serine levels. Mechanistically, UTX recruits E3 ligase RNF114 to ubiquitinate phosphoglycerate dehydrogenase, the rate limiting enzyme for de novo serine synthesis, at Lys³¹⁰ and Lys³³⁰, which leads to its degradation, and thus suppresses renal and circulating serine levels. Consistently, phosphoglycerate dehydrogenase and serine levels are markedly downregulated in human subjects with diabetic kidney disease or obesity-related renal dysfunction. Notably, oral administration of serine ameliorates high-fat diet induced fatty liver and renal dysfunction, suggesting a potential approach against obesity related metabolic disorders. Together, our results reveal a metabolic homeostasis regulation mediated by a renal UTX-PHGDH-serine axis.

The Iberian pig fed with high-fat diet: a model of renal disease in obesity and metabolic syndrome

BACKGROUND

The pathogenesis of renal disease in the context of overweight/obesity, metabolic syndrome, and insulin resistance is not completely understood. This may be due to the lack of a definitive animal model of disease, which limits our understanding of obesity-induced renal damage. We evaluated the changes in renal histology and lipid deposits induced by obesity in a model of insulin resistance: the Iberian swine fed with fat-enriched food.

METHODS

Twenty-eight female sows were randomized to standard (SD) or high-fat diet (HFD: 6.8% of saturated fat) for 100 days. Weight, adiposity, analytics, oral glucose tolerance tests, and measured renal function were determined. Renal histology and lipid deposits in renal tissue were analyzed.

RESULTS

Animals on HFD developed obesity, hypertension, high levels of LDL cholesterol, triglycerides, insulin resistance, and glomerular hyperfiltration. No animal developed overt diabetes. Animals on HFD showed "diabetoid changes", including mesangial expansion [21.40% ± 4 vs.13.20% ± 4.0, p < 0.0001], nodular glomerulosclerosis [7.40% ± 7, 0.75 vs. 2.40% ± 4.7, p = 0.02], and glomerulomegaly (18% vs. 10%, p = 0.010) than those on SD. Tubular atrophy, interstitial fibrosis, inflammation, arteriolar hyalinosis, or fibrointimal thickening were mild and similar between groups. Triglyceride content in renal tissue was higher in animals on HFD than in SD (15.4% ± 0.5 vs. 12.7% ± 0.7; p < 0.01).

CONCLUSIONS

Iberian pigs fed with fat-enriched food showed diabetoid changes and glomerulomegaly as observed in obese humans making this model suitable to study obesity-induced renal disease.

Changes in hormone profiles, growth factors, and mRNA expression of the related receptors in crop tissue, relative organ weight, and serum biochemical parameters in the domestic pigeon (Columba livia) during incubation and chick-rearing periods under artificial farming conditions

The present study was conducted to determine the changes in concentrations of hormones and growth factors and their related receptor gene expressions in crop tissue, relative organ weight, and serum biochemical parameters in male and female pigeons during incubation and chick-rearing periods under artificial farming conditions. Seventy-eight pairs of 60-week-old White King pigeons with 2 fertile eggs per pair were randomly divided into 13 groups by different breeding stages. Serum prolactin and insulin-like growth factor-1 (IGF-1) concentrations in crop tissue homogenates were the highest in both male and female pigeons at 1 d of chick-rearing (R1), while epidermal growth factor (EGF) in female pigeons peaked at d 17 of incubation (I17) (P < 0.05). mRNA expression of the prolactin and EGF receptors in the crop tissue increased at the end of incubation and the early chick-rearing stage in both sexes. However, estrogen, progesterone, and growth hormone receptor expression each decreased during the early chick-rearing stage (P < 0.05). In male pigeons, IGF-1 receptor gene expression reached its peak at R7, while in female pigeons, it increased at the end of incubation. The relative weight of breast and abdominal fat in both sexes and thighs in the males was lowest at R7, and then gradually increased to the incubation period level. Serum total protein, albumin, and globulin concentrations increased to the highest levels at I17 (P < 0.05). Total cholesterol, triglyceride, and low-density lipoprotein reached their highest values at I17 in male pigeons and R25 in female pigeons (P < 0.05). In conclusion, hormones, growth factors, and their receptors potentially underlie pigeon crop tissue development. Changes in organs and serum biochemical profiles suggested their different breeding-cycle patterns with sexual effects.

SCAP/SREBPs are Central Players in Lipid Metabolism and Novel Metabolic Targets in Cancer Therapy

Lipid metabolism reprogramming emerges as a new hallmark of malignancies. Sterol regulatory element-binding proteins (SREBPs), which are central players in lipid metabolism, are endoplasmic reticulum (ER)-bound transcription factors that control the expression of genes important for lipid synthesis and uptake. Their transcriptional activation requires binding to SREBP cleavageactivating protein (SCAP) to translocate their inactive precursors from the ER to the Golgi to undergo cleavage and subsequent nucleus translocation of their NH2-terminal forms. Recent studies have revealed that SREBPs are markedly upregulated in human cancers, providing the mechanistic link between lipid metabolism alterations and malignancies. Pharmacological or genetic inhibition of SCAP or SREBPs significantly suppresses tumor growth in various cancer models, demonstrating that SCAP/SREBPs could serve as promising metabolic targets for cancer therapy. In this review, we will summarize recent progress in our understanding of the underlying molecular mechanisms regulating SCAP/SREBPs and lipid metabolism in malignancies, discuss new findings about SREBP trafficking, which requires SCAP N-glycosylation, and introduce a newly identified microRNA-29-mediated negative feedback regulation of the SCAP/SREBP pathway. Moreover, we will review recently developed inhibitors targeting the SCAP/SREBP pathway for cancer treatment.

Nutritive values, flavor amino acids, healthcare fatty acids and flesh quality improved by manganese referring to up-regulating the antioxidant capacity and signaling molecules TOR and Nrf2 in the muscle of fish

Flesh quality, amino acid and fatty acid composition, antioxidant status and related molecule expression in fish muscle were estimated by feeding grass carp with diets containing 3.65-27.86mg/kg diet of manganese (Mn) for 8weeks. Results demonstrated that optimal Mn increased toughness, collagen content, and pH, and decreased the cooking loss, and cathepsin B and L activities to enhance the flesh quality of fish. Meanwhile, optimal Mn increased the protein, lipid, the total essential amino acid (AA) (especially umami AA), and healthcare fatty acids, C18: 1c+t, C20: 3n-3, C20: 4 and DHA contents. These might be partially related to the decreased lipid peroxidation and protein oxidation, and the enhanced activities of Mn superoxide dismutase (MnSOD), catalase (CAT) and glutathione peroxidase (GPx) modulated by their gene expression, Nrf2 and TOR signaling. We firstly demonstrated that Mn improved flesh quality, flavor and healthcare function in fish muscle.

Obesity-related glomerulopathy: clinical and pathologic characteristics and pathogenesis

The prevalence of obesity-related glomerulopathy is increasing in parallel with the worldwide obesity epidemic. Glomerular hypertrophy and adaptive focal segmental glomerulosclerosis define the condition pathologically. The glomerulus enlarges in response to obesity-induced increases in glomerular filtration rate, renal plasma flow, filtration fraction and tubular sodium reabsorption. Normal insulin/phosphatidylinositol 3-kinase/Akt and mTOR signalling are critical for podocyte hypertrophy and adaptation. Adipokines and ectopic lipid accumulation in the kidney promote insulin resistance of podocytes and maladaptive responses to cope with the mechanical forces of renal hyperfiltration. Although most patients have stable or slowly progressive proteinuria, up to one-third develop progressive renal failure and end-stage renal disease. Renin-angiotensin-aldosterone blockade is effective in the short-term but weight loss by hypocaloric diet or bariatric surgery has induced more consistent and dramatic antiproteinuric effects and reversal of hyperfiltration. Altered fatty acid and cholesterol metabolism are increasingly recognized as key mediators of renal lipid accumulation, inflammation, oxidative stress and fibrosis. Newer therapies directed to lipid metabolism, including SREBP antagonists, PPARα agonists, FXR and TGR5 agonists, and LXR agonists, hold therapeutic promise.

Obesity-Related Chronic Kidney Disease-The Role of Lipid Metabolism

Obesity is an independent risk factor for chronic kidney disease (CKD). The mechanisms linking obesity and CKD include systemic changes such as high blood pressure and hyperglycemia, and intrarenal effects relating to lipid accumulation. Normal lipid metabolism is integral to renal physiology and disturbances of renal lipid and energy metabolism are increasingly being linked with kidney disease. AMP-activated protein kinase (AMPK) and acetyl-CoA carboxylase (ACC) are important regulators of fatty acid oxidation, which is frequently abnormal in the kidney with CKD. A high fat diet reduces renal AMPK activity, thereby contributing to reduced fatty acid oxidation and energy imbalance, and treatments to activate AMPK are beneficial in animal models of obesity-related CKD. Studies have found that the specific cell types affected by excessive lipid accumulation are proximal tubular cells, podocytes, and mesangial cells. Targeting disturbances of renal energy metabolism is a promising approach to addressing the current epidemic of obesity-related kidney disease.

Superovulation Induced Changes of Lipid Metabolism in Ovaries and Embryos and Its Probable Mechanism

This research was intended to investigate the fetal origins of changed birth weight of the offspring born through assisted reproductive technology (ART). The association between hormone and lipid metabolism or body weight has been generally accepted, and as the basic and specific treatment in ART procedure, gonadotropin stimulation might have potential effects on intrauterine lipid metabolism. In our studies, the mice were superovulated with two doses of gonadotropin. The cholesterol metabolism in ovaries and the triglyceride metabolism in embryos were analyzed. The results showed gonadotropin probably accelerated luteinization and induced a longer time follicle development and ovulation, which resulted in histological and morphological alteration of ovary, and increased the cholesterol content and the expressions of steroidogenesis-related genes. In embryos, gonadotropin increased lipid accumulation and decreased fatty acid synthesis in a dose-dependent manner. Moreover, the changes of fatty acid composition were also shown in superovulation groups. Our studies firstly provided the evidence that the superovulation might affect the maternal and fetal lipid metabolism. These variations of lipid metabolism in our results may be associated with birth weight of ART infants.

Fatty kidney: emerging role of ectopic lipid in obesity-related renal disease

The global increase in chronic kidney disease (CKD) parallels the obesity epidemic. Obesity conveys a gradual but independent risk of progression of CKD that seems irrespective of the underlying nephropathy. Obesity has been associated with a secondary focal segmental glomerulosclerosis coined obesity-related glomerulopathy (ORG). Pathways through which obesity might cause renal disease are not well understood, and early clinical biomarkers for incipient ORG or renal relevant obesity are currently lacking. Recent human and experimental studies have associated ectopic lipid accumulation in the kidney (fatty kidney) with obesity-related renal disease. There is enough growing insight that ectopic lipid--the accumulation of lipid in non-adipose tissue--is associated with structural and functional changes of mesangial cells, podocytes, and proximal tubular cells to propose the development of ORG as a maladaptive response to hyperfiltration and albuminuria. Recent advances in metabolic imaging might validate ectopic lipid as a biomarker and research aid, to help translate novel therapeutics from experimental models to patients.

Absence of cumulus cells during in vitro maturation affects lipid metabolism in bovine oocytes

Cumulus cells (CC) surround the oocyte and are coupled metabolically through regulation of nutrient intake. CC removal before in vitro maturation (IVM) decreases bovine oocyte developmental competence without affecting nuclear meiotic maturation. The objective was to investigate the influence of CC on oocyte cytoplasmic maturation in relation to energy metabolism. IVM with either cumulus-enclosed (CEO) or -denuded (DO) oocytes was performed in serum-free metabolically optimized medium. Transmission electron microscopy revealed different distribution of membrane-bound vesicles and lipid droplets between metaphase II DO and CEO. By Nile Red staining, a significant reduction in total lipid level was evidenced in DO. Global transcriptomic analysis revealed differential expression of genes regulating energy metabolism, transcription, and translation between CEO and DO. By Western blot, fatty acid synthase (FAS) and hormone-sensitive phospholipase (HSL) proteins were detected in oocytes and in CC, indicating a local lipogenesis and lypolysis. FAS protein was significantly less abundant in DO that in CEO and more highly expressed in CC than in the oocytes. On the contrary, HSL protein was more abundant in oocytes than in CC. In addition, active Ser⁵⁶³-phosphorylated HSL was detected in the oocytes only after IVM, and its level was similar in CEO and DO. In conclusion, absence of CC during IVM affected lipid metabolism in the oocyte and led to suboptimal cytoplasmic maturation. Thus, CC may influence the oocyte by orienting the consumption of nutritive storage via regulation of local fatty acid synthesis and lipolysis to provide energy for maturation.

The conflicting effects of maternal nutrient restriction and early-life obesity on renal health

Epidemiological and animal studies have demonstrated that early-life nutrition alters the metabolic responses and generates structural changes in complex tissues, such as the kidneys, which may lead to a reduction in the offspring lifespan. Independently, obesity induces a spontaneous low-grade chronic inflammatory response by modulating several of the major metabolic pathways that ultimately compromise long-term renal health. However, the combined effects of maternal nutrition and early-life obesity in the development of renal diseases are far from conclusive. Previous results, using the ovine model, demonstrated that the combination of a reduction in fetal nutrition and juvenile obesity induced a series of adaptations associated with severe metabolic syndrome in the heart and adipose tissue. Surprisingly, exposure to an obesogenic environment in the kidney of those offspring produced an apparent reduction in glomerulosclerosis in relation to age- and weight-matched controls. However, this reduction in cellular apoptosis was accompanied by a rise in glomerular filtration rate and blood pressure of equal intensity when compared with obese controls. The intention of this review is to explain the adaptive responses observed in this model, based on insights into the mechanism of renal fetal programming, and their potential interactions with some of the metabolic changes produced by obesity.

IGF-1, IGFBP-3 and ALS in adult patients with chronic kidney disease

BACKGROUND

Insulin-like growth factor I (IGF-1) is for the most part bound in a ternary complex with IGF-binding protein-3 (IGFBP-3) and acid-labile subunit (ALS). This ternary complex is a storage form of IGF-1 in blood and passes not through the renal glomerulus. Little information is available in regard to the components of the ternary complex in adult renal disease.

OBJECTIVE

To investigate levels of serum IGF-1, IGFBP-3 and ALS in relation to renal function and extent of proteinuria.

DESIGN AND PATIENTS

We measured IGF-1, IGFBP-3 and ALS concentrations in 137 patients who were investigated due to proteinuria and/or haematuria and/or renal impairment. The patients received renal biopsies and the histological diagnosis was documented. Urinary albumin excretion and relevant clinical parameter were evaluated.

RESULTS

IGF-1 showed a highly positive correlation to IGFBP-3 and ALS, and the latter to IGFBP-3. IGF-1, IGFBP-3 and ALS decreased with increasing age. IGF-1 and IGFBP-3 showed no significant change depending on the creatinine clearance. However, ALS decreased with decreasing renal function. In patients with heavy proteinuria ALS levels, but not IGF-1 and IGFBP-3 levels, decreased significantly. Patients with chronic ischaemic renal damage and diabetic glomerulopathy showed higher IGF-1 and IGFBP-3 levels compared to patients with thin glomerular basement membrane disease despite their older age.

CONCLUSIONS

IGF-1 and IGFBP-3 levels seem to be independent of renal function and severity of proteinuria. However, ALS levels are altered in renal failure and nephrotic syndrome, which may be due to increased renal loss or diminished hepatic production or both.

Association between metabolic syndrome and chronic kidney disease in the Korean population

AIM

We performed a retrospective study to examine the association between the metabolic syndrome (MS)and risk for the development of chronic kidney disease (CKD).

METHODS

This cohort study included 60 921 healthy adults recruited from two health promotion centres.Anthropometric measures, blood pressure, fasting glucose, lipid profile and serum creatinine were evaluated. The glomerular filtration rate was estimated (eGFR) using the abbreviated equation developed by the Modification of Diet in Renal Disease (MDRD) formula. CKD was defined as an eGFR of <60 mL/min per 1.73 m2 or the presence of proteinuria.

RESULTS

The prevalence of MS and CKD was 19.0% and 7.2% respectively. Those with MS had a higher prevalence of CKD (11.0% vs 6.3%, P < 0.001) than those without MS. As the number of MS components increased, the prevalence of CKD increased and the eGFR decreased. The multiple linear analyses showed that each of the components of the MS was negatively correlated with the eGFR. Unadjusted and multivariate adjusted associations were identified between MS and CKD. Individuals with MS had a multivariate adjusted odds ratio of 1.680 (95% confidence interval, 0.566-1.801) for CKD compared with those without MS.

CONCLUSION

Our findings, which were obtained from a large Korean cohort, suggest that MS was associated with CKD.

Novel roles of the IGF-IGFBP axis in etiopathophysiology of diabetic nephropathy

Mechanisms contributing to development of diabetic nephropathy (DN) remain unclear. High ambient glucose level transforms intracellular pathways, promoting stable phenotypic changes in the glomerulus such as mesangial cell hypertrophy, podocyte apoptosis, and matrix expansion. Insulin-like growth factors (IGFs) and the high affinity IGF binding proteins (IGFBPs) exert major effects on cell growth and metabolism. Compared with diabetic patients without microalbuminuria (MA), MA diabetic patients display perturbed GH-IGF-IGFBP homeostasis, including increased circulating IGF-I and IGFBP-3 protease activity, increased excretion of bioactive GH, IGF-I, and IGFBP-3, but decreased circulating IGFBP-3 levels. In diabetic animal models, expression of IGF-I and IGFBP-1 to -4 increases in key renal tissues and glomerular ulrafiltrate. Epithelial, mesangial, and endothelial cells derived from the kidney respond to IGF-I binding with increased protein synthesis, migration, and proliferation. This article reviews classic and emerging concepts for the roles of the GH-IGF-IGFBP axis in the etiopathophysiology, treatment, and prevention of diabetic renal disease. We report IGF-independent actions of IGFBP-3 in the podocyte for the first time.

Obesity and obesity-initiated metabolic syndrome: mechanistic links to chronic kidney disease

There is an epidemic of obesity and the metabolic syndrome in the United States and across the world. Both entities are associated with high mortality, mainly as a result of cardiovascular disease. The epidemic of obesity has been paralleled by an increase in the incidence of chronic kidney disease (CKD). Several recent epidemiologic studies have shown that obesity and the metabolic syndrome are independent predictors of CKD. In addition to diabetes and hypertension, several other mechanisms have been postulated to initiate and maintain kidney injury in patients with obesity and the metabolic syndrome. This article reviews the recent epidemiologic data linking obesity and the metabolic syndrome to CKD and summarizes the potential mechanisms of renal injury in this setting, with a focus on the role of inflammation, lipotoxicity, and hemodynamic factors. Potential preventive and therapeutic modalities based on the limited evidence available are discussed.

Rat glomerular mesangial cells require laminin-9 to migrate in response to insulin-like growth factor binding protein-5

Temporal and spatial differences in extracellular matrix play critical roles in cell proliferation, differentiation and migration. Different migratory stimuli use different substrates and receptors to achieve cell migration. To understand the mechanism of insulin-like growth factor binding protein-5 (IGFBP-5)-induced migration in mesangial cells, the roles of integrins and substrates were examined. IGFBP-5 induced an increase in mRNA expression for laminin (LN) chains lama4, lamb2, and lamc1, suggesting that LN-9 might be required for migration. Antibodies to the LNalpha(4) and LNbeta(2) chains, but not LNbeta(1), blocked IGFBP-5-induced migration. Anti-sense morpholino oligonucleotide inhibition of expression of LNalpha(4) substantially reduced expression of LN-8/9 (alpha(4)beta(1)gamma(1)/alpha(4)beta(2)gamma(1), 411/421) and prevented IGFBP-5-induced migration. Anti-sense inhibition of lamb2 reduced expression of LN-9. Absence of LN-9 prevented IGFBP-5-induced migration, which was not preserved by continued expression of LN-8. The requirement for LN-9 was further supported by studies of T98G cells, which express predominantly LN-8. IGFBP-5 had little effect on migration in these cells, but increased migration when T98G cells were plated on LN-8/9. IGFBP-5-mediated mesangial cell migration was inhibited by antibodies that block attachment to alpha(6)beta(1)-integrins but was unaffected by antibodies and disintegrins that block binding to other integrins. Furthermore, in cells with anti-sense inhibited expression of LN-9, integrin alpha(6)beta(1) was no longer detected on the cell surface. These studies suggest the specificity of mechanisms of migration induced by specific stimuli and for the first time demonstrate a unique function for LN-9 in mediating IGFBP-5-induced migration.

Levosimendan protects against experimental endotoxemic acute renal failure

Endotoxemia induces a hemodynamic form of acute renal failure (ARF; renal vasoconstriction +/- reduced glomerular ultrafiltration coefficient, K(f); minimal/no histological damage). We tested whether levosimendan (LS), an ATP-sensitive K+ (K(ATP)) channel opener with cardiac ionotropic and possible anti-inflammatory properties, might have utility in combating this form of ARF. CD-1 mice were injected with LPS +/- LS. LS effects on LPS-induced systemic inflammation (plasma TNF-alpha/MCP-1; cardiorenal mRNAs), plasma NO levels, and azotemia were assessed. Because K(ATP) channel opening has been reported to mediate hypoxic tubular injury, possible adverse LS effects on ischemic ARF and ATP depletion injury were sought. Effects of diazoxide (another K(ATP) channel agonist) and glibenclamide (a channel antagonist) on hypoxic tubular injury also were assessed. Finally, the ability of LS to alter rat mesangial cell (MC) contraction in response to ANG II (elevated in sepsis) was tested. LS conferred almost complete protection against LPS-induced ARF, without any apparent reduction in the LPS-induced inflammatory response. Neither LS nor diazoxide altered ATP depletion-mediated tubule injury (in vivo or in vitro). Conversely, glibenclamide induced a marked and direct cytotoxic effect. LS completely blocked ANG II-induced MC contraction, an action likely to increase K(f). We concluded that 1) LS can confer marked protection against LPS-induced ARF; 2) this likely stems from vasoactive properties, rather than reductions in LPS-induced inflammation; and 3) K(ATP) channel agonists (but not antagonists) appear to be devoid of toxic proximal tubular cell effects. This suggests that LS, and other K(ATP) channel agonists, have a margin of safety if employed in situations (sepsis syndrome, heart failure) in which severe renal vasoconstriction might lead to ischemic ARF.

IGF-1 induces rat glomerular mesangial cells to accumulate triglyceride

Rat glomerular mesangial cells (MC) become lipid-laden foam cells when they are exposed to IGF-1. IGF-1 increased accumulation of triglyceride (TG) 2.5-fold in MC after 7 days. TG accumulation resulted from enhanced macropinocytosis and decreased efflux secondary to a 40-50% reduction in peroxisome proliferator-activated receptor (PPAR)-delta (PPARdelta). There was no evidence of primary or secondary changes in cholesterol or TG synthesis, increased uptake by LDL or scavenger receptors, or reduced efflux via ATP-binding cassette A-1. Although the lipid moiety taken up can be influenced by the concentration of cholesterol or TG in the medium, in standard medium MC preferentially accumulate TG. TG-rich MC foam cells fail to contract in response to angiotensin II (Berfield AK, Andress DL, and Abrass CK. Kidney Int 62: 1229-1237, 2002); however, their migratory response to IGF binding protein-5 is unaffected. This differs from cholesterol loading, which impairs both phagocytosis and migration. These findings have important implications for understanding the mechanisms that contribute to lipid accumulation in MC and the functional consequences of different forms of foam cells. These observations are relevant to understanding vascular disease and progressive renal diseases that are accelerated by abnormalities in lipid metabolism.

Saturated free fatty acids and apoptosis in microvascular mesangial cells: palmitate activates pro-apoptotic signaling involving caspase 9 and mitochondrial release of endonuclease G

Background

In type 2 diabetes, free fatty acids (FFA) accumulate in microvascular cells, but the phenotypic consequences of FFA accumulation in the microvasculature are incompletely understood. Here we investigated whether saturated FFA induce apoptosis in human microvascular mesangial cells and analyzed the signaling pathways involved.

Methods

Saturated and unsaturated FFA-albumin complexes were added to cultured human mesangial cells, after which the number of apoptotic cells were quantified and the signal transduction pathways involved were delineated.

Results

The saturated FFA palmitate and stearate were apoptotic unlike equivalent concentrations of the unsaturated FFA oleate and linoleate. Palmitate-induced apoptosis was potentiated by etomoxir, an inhibitor of mitochondrial β-oxidation, but was prevented by an activator of AMP-kinase, which increases fatty acid β-oxidation. Palmitate stimulated an intrinsic pathway of pro-apoptotic signaling as evidenced by increased mitochondrial release of cytochrome-c and activation of caspase 9. A caspase 9-selective inhibitor blocked caspase 3 activation but incompletely blocked apoptosis in response to palmitate, suggesting an additional caspase 9-independent pathway. Palmitate stimulated mitochondrial release of endonuclease G by a caspase 9-independent mechanism, thereby implicating endonuclease G in caspase 9-indpendent regulation of apoptosis by saturated FFA. We also observed that the unsaturated FFA oleate and linoleate prevented palmitate-induced mitochondrial release of both cytochrome-c and endonuclease G, which resulted in complete protection from palmitate-induced apoptosis.

Conclusions

Taken together, these results demonstrate that palmitate stimulates apoptosis by evoking an intrinsic pathway of proapoptotic signaling and identify mitochondrial release of endonuclease G as a key step in proapoptotic signaling by saturated FFA and in the anti-apoptotic actions of unsaturated FFA.

Attenuation of mouse mesangial cell contractility by high glucose and mannitol: involvement of protein kinase C and focal adhesion kinase

Hyperglycemia and mannitol activate protein kinase C (PKC) and induce mesangial cell hypocontractility that subsequently may modulate renal function. Since focal adhesion kinase (FAK) activation is known to be linked with PKC activity, FAK may also be involved in mesangial cell contraction. To facilitate our understanding of the PKC- and FAK-modulating mechanism, we developed an in vitro model of mouse mesangial cell hypocontractility induced by hyperglycemia or mannitol. Mouse mesangial cells (CRL-1927) were exposed to: normal D-glucose (group N), high D-glucose (group H), and control groups at the same osmolality as H plus L-glucose (group L) and mannitol (group M). Changes in the planar surface area of cells in response to 1 microM phorbol 12-myristate 13-acetate (PMA) were determined. Western blot analyses for PKC, phosphorylated (p)-PKC, tyrosine phosphorylation, FAK, and p-FAK were done on each of these four groups. The effects of mannitol in various doses on cell contraction and activation of PKC and FAK were also assayed. The planar surface areas of groups H and M both showed an attenuated change in response to PMA stimulation. Before PMA stimulation, the baseline PKC expression of groups H and M showed a higher expression of p-PKC alpha and delta than that seen in group N (p < 0.05). Results of tyrosine phosphorylation and immunoprecipitation showed that FAK may be involved in this contraction process. The total amount of FAK showed no significant difference among the four experimental groups; however, p-FAK was found to have significantly increased in group M (p < 0.05). The use of PKC and tyrosine kinase inhibitors reduced PMA-induced mesangial cell contraction in all four groups. Activation of PKC alpha, delta, and FAK with the resultant inhibition of mesangial cell contraction by mannitol was found to be dose-dependent. These results may provide a correlation between increased expression of several PKC isoforms and, in particular, increased phosphorylation levels of PKC alpha and delta and hypocontractility induced by high glucose and mannitol treatment. Furthermore, the mannitol-induced hypocontractility involving PKC and FAK occurred in a dose-dependent manner.

New concepts: growth hormone, insulin-like growth factor-I and the kidney

Both growth hormone (GH) and IGF-1 have major effects on normal kidney growth, structure and function and participate in the pathogenesis of certain kidney diseases. Furthermore when the kidneys fail there are profound changes in the circulating GH-IGF-1 system and the renal and systemic responses to these hormones. In this brief review we address the advances that have been made in our understanding of the relationship between growth hormone GH and IGF-1 and the kidney in health and the systemic and local perturbations that occur in kidney disease and identify key unanswered questions.