Short term exposure to elevated levels of leptin reduces proximal tubule cell metabolic activity

Expression of leptin receptor in renal tubules is sparse but implicated in leptin-dependent kidney gene expression and function

Leptin regulates energy balance via leptin receptors expressed in central and peripheral tissues, but little is known about leptin-sensitive kidney genes and the role of the tubular leptin receptor (Lepr) in response to a high-fat diet (HFD). Quantitative RT-PCR analysis of Lepr splice variants A, B, and C revealed a ratio of ∼100:10:1 in the mouse kidney cortex and medulla, with medullary levels being ∼10 times higher. Leptin replacement in ob/ob mice for 6 days reduced hyperphagia, hyperglycemia, and albuminuria, associated with normalization of kidney mRNA expression of molecular markers of glycolysis, gluconeogenesis, amino acid synthesis, and megalin. Normalization of leptin for 7 h in ob/ob mice did not normalize hyperglycemia or albuminuria. Tubular knockdown of Lepr [Pax8-Lepr knockout (KO)] and in situ hybridization revealed a minor fraction of Lepr mRNA in tubular cells compared with endothelial cells. Nevertheless, Pax8-Lepr KO mice had lower kidney weight. Moreover, while HFD-induced hyperleptinemia, increases in kidney weight and glomerular filtration rate, and a modest blood pressure lowering effect were similar compared with controls, they showed a blunted rise in albuminuria. Use of Pax8-Lepr KO and leptin replacement in ob/ob mice identified acetoacetyl-CoA synthetase and gremlin 1 as tubular Lepr-sensitive genes that are increased and reduced by leptin, respectively. In conclusion, leptin deficiency may increase albuminuria via systemic metabolic effects that impinge on kidney megalin expression, whereas hyperleptinemia may induce albuminuria by direct tubular Lepr effects. Implications of Lepr variants and the novel tubular Lepr/acetoacetyl-CoA synthetase/gremlin 1 axis remain to be determined.NEW & NOTEWORTHY This study provides new insights into kidney gene expression of leptin receptor splice variants, leptin-sensitive kidney gene expression, and the role of the leptin receptor in renal tubular cells for the response to diet-induced hyperleptinemia and obesity including albuminuria.

The Causes and Potential Injurious Effects of Elevated Serum Leptin Levels in Chronic Kidney Disease Patients

Leptin is an adipokine that regulates appetite and body mass and has many other pleiotropic functions, including regulating kidney function. Increased evidence shows that chronic kidney disease (CKD) is associated with hyperleptinemia, but the reasons for this phenomenon are not fully understood. In this review, we focused on potential causes of hyperleptinemia in patients with CKD and the effects of elevated serum leptin levels on patient kidney function and cardiovascular risk. The available data indicate that the increased concentration of leptin in the blood of CKD patients may result from both decreased leptin elimination from the circulation by the kidneys (due to renal dysfunction) and increased leptin production by the adipose tissue. The overproduction of leptin by the adipose tissue could result from: (a) hyperinsulinemia; (b) chronic inflammation; and (c) significant lipid disturbances in CKD patients. Elevated leptin in CKD patients may further deteriorate kidney function and lead to increased cardiovascular risk.

CB1 receptor antagonist rimonabant protects against chronic intermittent hypoxia-induced renal injury in rats

BACKGROUND

Obstructive sleep apnoea (OSA) induced chronic kidney disease is mainly caused by chronic intermittent hypoxia (CIH). Our study investigate the mechanism underlying CIH-induced renal damage and whether the cannabinoid receptor 1 (CB1R) antagonist rimonabant (Ri) alleviates CIH-induced renal injury.

METHODS

Male Sprague-Dawley rats were randomly divided into five groups: one normal control (NC) group, two chronic intermittent hypoxia (CIH) groups, and two CIH + Ri groups. Rats in the NC groups were exposed to room air, while the CIH groups were exposed to a CIH environment for 4 weeks (4w CIH group) and 6 weeks (6w CIH group), respectively. Additionally, rats in the CIH + Ri groups were administered 1.5 mg/kg/day Ri for 4 weeks (4w CIH + Ri group) and 6 weeks (6w CIH + Ri group), respectively. Following this, the rats were euthanized and kidneys were excised for downstream analysis. In the renal tissues, the morphological alterations were examined via haematoxylin eosin (HE) staining and periodic acid schiff (PAS) staining, CB1R, Fis1, Mfn1, and p66Shc expression was assessed through western blot and immunohistochemistry, and the mitochondrial ultrastructural changes in kidney sections were assessed by electron microscopy.

RESULTS

CB1R expression in the 4w and 6w CIH groups was significantly elevated, and further increased with prolonged hypoxia; however, Ri prevented the increase in CIH-induced CB1R expression. Fis1 and p66Shc expression in the CIH groups were increased, but Mfn1 expression decreased. Ri decreased Fis1 and p66Shc expression and increased Mfn1 expression. Renal damage in the 4w or 6w CIH + Ri group was evidently improved compared with that in the 4w or 6w CIH group. CB1R expression was positively correlated with Fis1 and p66Shc and negatively correlated with Mfn1. Meanwhile, electron microscopy showed that the percentage of fragmented mitochondria in the tubular cells in each group was consistent with the trend of CB1R expression.

CONCLUSION

CIH causes endocannabinoid disorders and induces abnormal mitochondrial dynamics, resulting in renal injury. Treatment with CB1R antagonists reduces CIH-induced renal damage by inhibiting dysregulated renal mitochondrial dynamics.

Endocannabinoid System and the Kidneys: From Renal Physiology to Injury and Disease

Introduction: As the prevalence of kidney disease continues to rise worldwide, there is accumulating evidence that kidney injury and dysfunction, whether acute or chronic, is associated with major adverse outcomes, including mortality. Meanwhile, effective therapeutic options in the treatment of acute kidney injury (AKI) and chronic kidney disease (CKD) have been sparse. Many of the effective treatments that are routinely utilized for different pathologies in patients without kidney disease have failed to demonstrate efficacy in those with renal dysfunction. Hence, there is an urgent need for discovery of novel pathways that can be targeted for innovative and effective clinical therapies in renal disease states.

Discussion: There is now accumulating evidence that the endocannabinoid (EC) system plays a prominent role in normal renal homeostasis and function. In addition, numerous recent studies have described mechanisms through which alteration in the EC system can contribute to kidney damage and disease. These include a potential role for cannabinoid receptors in tubulo-glomerular damage and fibrosis, which are common features of AKI, interstitial nephritis, glomerulopathy, and other conditions leading to AKI and CKD.

Conclusion: These findings suggest that manipulating the EC system may be an effective therapeutic strategy for the treatment of kidney disease and injury. However, further mechanistic studies are needed to fully delineate the role of this system in various conditions affecting the kidneys. Furthermore, while most of the current literature is focused on the role of the EC system as a whole in renal pathophysiology, future studies will also need to clarify the contribution of each component of this system, including the EC mediators, in the pathogenesis of kidney disease and their potential role as part of a therapeutic strategy.

Uteroplacental insufficiency in rats induces renal apoptosis and delays nephrogenesis completion

AIM

Uteroplacental insufficiency in rats reduces nephron endowment, leptin concentrations and programmes cardiorenal disease in offspring. Cross-fostering growth-restricted (Restricted) offspring onto a mother with normal lactation restores leptin concentrations and nephron endowment. This study aimed to determine whether the reduced nephron endowment in Restricted offspring is due to delayed glomerular formation and dysregulation of renal genes regulating branching morphogenesis, apoptosis or leptin signalling. Furthermore, we aimed to investigate whether cross-fostering Restricted offspring onto Control mothers could improve glomerular maturation and restore renal gene abundance.

METHODS

Uteroplacental insufficiency was induced by bilateral uterine vessel ligation (Restricted) or sham (Control) surgery on gestation day 18 (E18). Kidneys were collected at E20, postnatal day 1 (PN1) and PN7. An additional cohort was cross-fostered onto separate mothers at birth and kidneys collected at PN7.

RESULTS

Kidneys were lighter in the Restricted group, but weight was restored with cross-fostering. At E20, abundance of Bax, Flt1 and Vegfa was increased in Restricted offspring, while Ret and Bcl2 transcripts were increased only in Restricted females. At PN7, abundance of Gdnf and Ret was higher in Restricted offspring, as was Casp3. Restricted offspring had a wider nephrogenic zone with more immature glomeruli suggesting a delayed or extended nephrogenic period. Cross-fostering had subtle effects on gene abundance and glomerular maturity.

CONCLUSION

Uteroplacental insufficiency induced apoptosis in the developing kidney and delayed and extended nephrogenesis. Cross-fostering Restricted offspring onto Control mothers had beneficial effects on kidney growth and renal maturity, which may contribute to the restoration of nephron endowment.

Cannabinoid receptors in the kidney

PURPOSE OF REVIEW

The endocannabinoid system modulates cell signaling targets that are essential for energy homeostasis. Endocannabinoids bind to G protein-coupled receptors in the central nervous system and periphery, including the kidney. Modulation of cannabinoid receptor 1 (CB1) and CB2 activity in the kidney in diabetes and obesity has been identified as potential therapeutic target to reduce albuminuria and renal fibrosis. This review will highlight the results of recent studies that have identified a role for CB1 and CB2 in normal and pathological renal conditions.

RECENT FINDINGS

CB1 and CB2 have been reported to play key roles in renal function and dysfunction. Recent studies have determined that antagonism of CB1 and agonism of CB2 in diabetic nephropathy and obesity associated kidney disease can reduce albuminuria, potentially by acting on both the glomeruli and tubules. Emerging studies have also identified a role for CB1 in renal diseases associated with fibrosis, with CB1 upregulated in multiple models of human nephropathies.

SUMMARY

Emerging studies using isolated cells, rodent models, and human studies have identified a critical role for the endocannabinoid system in renal function and disease. Thus, therapeutics that modulate the activity of CB1 and CB2 in renal disease could become clinically relevant.

Uteroplacental insufficiency reduces rat plasma leptin concentrations and alters placental leptin transporters: ameliorated with enhanced milk intake and nutrition

KEY POINTS

Uteroplacental insufficiency compromises maternal mammary development, milk production and pup organ development; this is ameliorated by cross-fostering, which improves pup growth and organ development and prevents adult diseases in growth-restricted (Restricted) offspring by enhancing postnatal nutrition. Leptin is transported to the fetus from the mother by the placenta; we report reduced plasma leptin concentrations in Restricted fetuses associated with sex-specific alterations in placental leptin transporter expression. Pup plasma leptin concentrations were also reduced during suckling, which may suggest reduced milk leptin transport or leptin reabsorption. Mothers suckled by Restricted pups had impaired mammary development and changes in milk fatty acid composition with no alterations in milk leptin; cross-fostering restored pup plasma leptin concentrations, which may be correlated to improved milk composition and intake. Increased plasma leptin and altered milk fatty acid composition in Restricted pups suckling mothers with normal lactation may improve postnatal growth and prevent adult diseases.

ABSTRACT

Uteroplacental insufficiency reduces birth weight and adversely affects fetal organ development, increasing adult disease risk. Cross-fostering improves postnatal nutrition and restores these deficits. Mothers with growth-restricted pups have compromised milk production and composition; however, the impact cross-fostering has on milk production and composition is unknown. Plasma leptin concentrations peak during the completion of organogenesis, which occurs postnatally in rats. Leptin is transferred to the fetus via the placenta and to the pup via the lactating mammary gland. This study investigated the effect of uteroplacental insufficiency on pup plasma leptin concentrations and placental leptin transporters. We additionally examined whether cross-fostering improves mammary development, milk composition and pup plasma leptin concentrations. Fetal growth restriction was induced by bilateral uterine vessel ligation surgery on gestation day 18 in Wistar Kyoto rats (termed uteroplacental insufficiency surgery mothers). Growth-restricted (Restricted) fetuses had reduced plasma leptin concentrations, persisting throughout lactation, and sex-specific alterations in placental leptin transporters. Mothers suckled by Restricted pups had impaired mammary development, altered milk fatty acid composition and increased plasma leptin concentrations, despite no changes in milk leptin. Milk intake was reduced in Restricted pups suckling uteroplacental insufficiency surgery mothers compared to Restricted pups suckling sham-operated mothers. Cross-fostering Restricted pups onto a sham-operated mother improved postnatal growth and restored plasma leptin concentrations compared to Restricted pups suckling uteroplacental insufficiency surgery mothers. Uteroplacental insufficiency alters leptin homeostasis. This is ameliorated with cross-fostering and enhanced milk fatty acid composition and consumption, which may protect the pups from developing adverse health conditions in adulthood.

Obesity and kidney disease: Beyond the hyperfiltration

In industrialized countries, overweight and obesity account for approximately 13.8% and 24.9% of the kidney disease observed in men and women, respectively. Moreover, obesity-associated glomerulopathy is now considered as "an emerging epidemic." Kidney function can be negatively impacted by obesity through several mechanisms, either direct or indirect. While it is well established that obesity represents the leading risk factor for type 2 diabetes and hypertension, awareness that obesity is associated with direct kidney damage independently of hypertension and diabetes is still not widespread. In this paper we will discuss the emerging role of adipose tissue, particularly in the visceral depot, in obesity-induced chronic kidney damage.

Leptin in pregnancy and development: a contributor to adulthood disease?

Emerging research has highlighted the importance of leptin in fetal growth and development independent of its essential role in the maintenance of hunger and satiety through the modulation of neuropeptide Y and proopiomelanocortin neurons. Alterations in maternal-placental-fetal leptin exchange may modify the development of the fetus and contribute to the increased risk of developing disease in adulthood. In addition, leptin also plays an important role in reproductive functions, with plasma leptin concentrations rising in pregnant women, peaking during the third trimester. Elevated plasma leptin concentrations occur at the completion of organogenesis, and research in animal models has demonstrated that leptin is involved in the development and maturation of a number of organs, including the heart, brain, kidneys, and pancreas. Elevated maternal plasma leptin is associated with maternal obesity, and reduced fetal plasma leptin is correlated with intrauterine growth restriction. Alterations in plasma leptin during development may be associated with an increased risk of developing a number of adulthood diseases, including cardiovascular, metabolic, and renal diseases via altered fetal development and organogenesis. Importantly, research has shown that leptin antagonism after birth significantly reduces maturation of numerous organs. Conversely, restoration of the leptin deficiency after birth in growth-restricted animals restores the offspring's body weight and improves organogenesis. Therefore, leptin appears to play a major role in organogenesis, which may adversely affect the risk of developing a number of diseases in adulthood. Therefore, greater understanding of the role of leptin during development may assist in the prevention and treatment of a number of disease states that occur in adulthood.

Acute leptin exposure reduces megalin expression and upregulates TGFβ1 in cultured renal proximal tubule cells

Increased leptin concentrations observed in obesity can lead to proteinuria, suggesting that leptin may play a role in obesity-related kidney disease. Obesity reduces activation of AMP-activated protein kinase (AMPK) and increases transforming growth factor-β1 (TGF-β1) expression in the kidney, leading to albuminuria. Thus we investigated if elevated leptin altered AMPK and TGF-β1 signaling in proximal tubule cells (PTCs). In opossum kidney (OK) PTCs Western blot analysis demonstrated that leptin upregulates TGF-β1 secretion (0.50 µg/ml) and phosphorylated AMPKα (at 0.25, and 0.50 µg/ml), and downregulates megalin expression at all concentrations (0.05-0.50 µg/ml). Using the AMPK inhibitor, Compound C, leptin exposure regulated TGF-β1 expression and secretion in PTCs via an AMPK mediated pathway. In addition, elevated leptin exposure (0.50 µg/ml) reduced albumin handling in OK cells independently of megalin expression. This study demonstrates that leptin upregulates TGF-β1, reduces megalin, and reduces albumin handling in PTCs by an AMPK mediated pathway.

Leptin inhibits the Na(+)/K(+) ATPase in Caco-2 cells via PKC and p38MAPK

We demonstrated previously an inhibitory effect of luminal leptin on glucose absorption in differentiated Caco-2 cells. Since this process is dependent on the Na(+) gradient established by the Na(+)/K(+)ATPase this work was undertaken to investigate if the ATPase is one of the hormone's targets. Fully differentiated Caco-2 cells were incubated with 10nM luminal leptin and the activity of the Na(+)/K(+) ATPase was assayed by measuring the amount of inorganic phosphate liberated. To elucidate the signaling pathway involved, the suspected mediators, namely PKC, p38MAPK, ERK and PI3K, were inhibited with specific pharmacological inhibitors and their implication was confirmed by determining changes in the protein expression of their active phosphorylated forms by Western blot analysis. Leptin reduced significantly the activity of the Na(+)/K(+) ATPase, by activating p38MAPK via inhibition of PKC, an upstream inhibitor of the kinase. ERK and PI3K are modulators of the pump and are not along the pathway activated by leptin but cross talk with it at the level of p38MAPK.

Adipokines as a link between obesity and chronic kidney disease

Adipocytes secrete a number of bioactive adipokines that activate a variety of cell signaling pathways in central and peripheral tissues. Obesity is associated with the altered production of many adipokines and is linked to a number of pathologies. As an increase in body weight is directly associated with an increased risk for developing chronic kidney disease (CKD), there is significant interest in the link between obesity and renal dysfunction. Altered levels of the adipokines leptin, adiponectin, resistin, and visfatin can decrease the glomerular filtration rate and increase albuminuria, which are pathophysiological changes typical of CKD. Specifically, exposure of the glomerulus to altered adipokine levels can increase its permeability, fuse the podocytes, and cause mesangial cell hypertrophy, all of which alter the glomerular filtration rate. In addition, the adipokines leptin and adiponectin can act on tubular networks. Thus, adipokines can act on multiple cell types in the development of renal pathophysiology. Importantly, most studies have been performed using in vitro models, with future studies in vivo required to further elucidate the specific roles that adipokines play in the development and progression of CKD.