Insulin receptors in the kidneys in health and disease

Identification of ligand and receptor interactions in CKD and MASH through the integration of single cell and spatial transcriptomics

BACKGROUND

Chronic Kidney Disease (CKD) and Metabolic dysfunction-associated steatohepatitis (MASH) are metabolic fibroinflammatory diseases. Combining single-cell (scRNAseq) and spatial transcriptomics (ST) could give unprecedented molecular disease understanding at single-cell resolution. A more comprehensive analysis of the cell-specific ligand-receptor (L-R) interactions could provide pivotal information about signaling pathways in CKD and MASH. To achieve this, we created an integrative analysis framework in CKD and MASH from two available human cohorts.

RESULTS

The analytical framework identified L-R pairs involved in cellular crosstalk in CKD and MASH. Interactions between cell types identified using scRNAseq data were validated by checking the spatial co-presence using the ST data and the co-expression of the communicating targets. Multiple L-R protein pairs identified are known key players in CKD and MASH, while others are novel potential targets previously observed only in animal models.

CONCLUSION

Our study highlights the importance of integrating different modalities of transcriptomic data for a better understanding of the molecular mechanisms. The combination of single-cell resolution from scRNAseq data, combined with tissue slide investigations and visualization of cell-cell interactions obtained through ST, paves the way for the identification of future potential therapeutic targets and developing effective therapies.

TYG Index as a Novel Predictor of Clinical Outcomes in Advanced Chronic Heart Failure with Renal Dysfunction Patients

Background

The triglyceride-glucose (TYG) index is a novel and reliable marker reflecting insulin resistance. Its predictive ability for cardiovascular disease onset and prognosis has been confirmed. However, for advanced chronic heart failure (acHF) patients, the prognostic value of TYG is challenged due to the often accompanying renal dysfunction (RD). Therefore, this study focuses on patients with aHF accompanied by RD to investigate the predictive value of the TYG index for their prognosis.

Methods and Results

717 acHF with RD patients were included. The acHF diagnosis was based on the 2021 ESC criteria for acHF. RD was defined as the eGFR < 90 mL/(min/1.73 m2). Patients were divided into two groups based on their TYG index values. The primary endpoint was major adverse cardiovascular events (MACEs), and the secondary endpoints is all-cause mortality (ACM). The follow-up duration was 21.58 (17.98-25.39) months. The optimal cutoff values for predicting MACEs and ACM were determined using ROC curves. Hazard factors for MACEs and ACM were revealed through univariate and multivariate COX regression analyses. According to the univariate COX regression analysis, high TyG index was identified as a risk factor for MACEs (hazard ratio = 5.198; 95% confidence interval [CI], 3.702-7.298; P < 0.001) and ACM (hazard ratio = 4.461; 95% CI, 2.962-6.718; P < 0.001). The multivariate COX regression analysis showed that patients in the high TyG group experienced 440.2% MACEs risk increase (95% CI, 3.771-7.739; P < 0.001) and 406.2% ACM risk increase (95% CI, 3.268-7.839; P < 0.001). Kaplan-Meier survival analysis revealed that patients with high TyG index levels had an elevated risk of experiencing MACEs and ACM within 30 months.

Conclusion

This study found that patients with high TYG index had an increased risk of MACEs and ACM, and the TYG index can serve as an independent predictor for prognosis.

Renal tubule-specific Atgl deletion links kidney lipid metabolism to glucagon-like peptide 1 and insulin secretion independent of renal inflammation or lipotoxicity

OBJECTIVE

Lipotoxic injury from renal lipid accumulation in obesity and type 2 diabetes (T2D) is implicated in associated kidney damage. However, models examining effects of renal ectopic lipid accumulation independent of obesity or T2D are lacking. We generated renal tubule-specific adipose triglyceride lipase knockout (RT-SAKO) mice to determine if this targeted triacylglycerol (TAG) over-storage affects glycemic control and kidney health.

METHODS

Male and female RT-SAKO mice and their control littermates were tested for changes in glycemic control at 10-12 and 16-18 weeks of age. Markers of kidney health and blood lipid and hormone concentrations were analyzed. Kidney and blood lysophosphatidic acid (LPA) levels were measured, and a role for LPA in mediating impaired glycemic control was evaluated using the LPA receptor 1/3 inhibitor Ki-16425.

RESULTS

All groups remained insulin sensitive, but 16- to 18-week-old male RT-SAKO mice became glucose intolerant, without developing kidney inflammation or fibrosis. Rather, these mice displayed lower circulating insulin and glucagon-like peptide 1 (GLP-1) levels. Impaired first-phase glucose-stimulated insulin secretion was detected and restored by Exendin-4. Kidney and blood LPA levels were elevated in older male but not female RT-SAKO mice, associated with increased kidney diacylglycerol kinase epsilon. Inhibition of LPA-mediated signaling restored serum GLP-1 levels, first-phase insulin secretion, and glucose tolerance.

CONCLUSIONS

TAG over-storage alone is insufficient to cause renal tubule lipotoxicity. This work is the first to show that endogenously derived LPA modulates GLP-1 levels in vivo, demonstrating a new mechanism of kidney-gut-pancreas crosstalk to regulate insulin secretion and glucose homeostasis.

Changes in Cells Associated with Insulin Resistance

Insulin is a polypeptide hormone synthesized and secreted by pancreatic β-cells. It plays an important role as a metabolic hormone. Insulin influences the metabolism of glucose, regulating plasma glucose levels and stimulating glucose storage in organs such as the liver, muscles and adipose tissue. It is involved in fat metabolism, increasing the storage of triglycerides and decreasing lipolysis. Ketone body metabolism also depends on insulin action, as insulin reduces ketone body concentrations and influences protein metabolism. It increases nitrogen retention, facilitates the transport of amino acids into cells and increases the synthesis of proteins. Insulin also inhibits protein breakdown and is involved in cellular growth and proliferation. On the other hand, defects in the intracellular signaling pathways of insulin may cause several disturbances in human metabolism, resulting in several chronic diseases. Insulin resistance, also known as impaired insulin sensitivity, is due to the decreased reaction of insulin signaling for glucose levels, seen when glucose use in response to an adequate concentration of insulin is impaired. Insulin resistance may cause, for example, increased plasma insulin levels. That state, called hyperinsulinemia, impairs metabolic processes and is observed in patients with type 2 diabetes mellitus and obesity. Hyperinsulinemia may increase the risk of initiation, progression and metastasis of several cancers and may cause poor cancer outcomes. Insulin resistance is a health problem worldwide; therefore, mechanisms of insulin resistance, causes and types of insulin resistance and strategies against insulin resistance are described in this review. Attention is also paid to factors that are associated with the development of insulin resistance, the main and characteristic symptoms of particular syndromes, plus other aspects of severe insulin resistance. This review mainly focuses on the description and analysis of changes in cells due to insulin resistance.

The role of endoplasmic reticulum-mitochondria-associated membranes in diabetic kidney disease

Diabetic kidney disease (DKD) is the leading cause of end-stage renal disease worldwide. The pathomechanisms of DKD are multifactorial, yet haemodynamic and metabolic changes in the early stages of the disease appear to predispose towards irreversible functional loss and histopathological changes. Recent studies highlight the importance of endoplasmic reticulum-mitochondria-associated membranes (ER-MAMs), structures conveying important cellular homeostatic and metabolic effects, in the pathology of DKD. Disruption of ER-MAM integrity in diabetic kidneys is associated with DKD progression, but the regulation of ER-MAMs and their pathogenic contribution remain largely unknown. Exploring the cell-specific components and dynamic changes of ER-MAMs in diabetic kidneys may lead to the identification of new approaches to detect and stratify diabetic patients with DKD. In addition, these insights may lead to novel therapeutic approaches to target and/or reverse disease progression. In this review, we discuss the association of ER-MAMs with key pathomechanisms driving DKD such as insulin resistance, dyslipidaemia, ER stress, and inflammasome activation and the importance of further exploration of ER-MAMs as diagnostic and therapeutic targets in DKD.

Targeting DNA methylation in diabetic kidney disease: A new perspective

Diabetic kidney disease (DKD) is a leading diabetic complication causing significant mortality among people around the globe. People with poor glycemic control accompanied by hyperinsulinemia, dyslipidemia, hypertension, and obesity develop diabetic complications. These diabetic patients develop epigenetic changes and suffer from diabetic kidney complications even after subsequent glucose control, the phenomenon that is recognized as metabolic memory. DNA methylation is an essential epigenetic modification that contributes to the development and progression of several diabetic complications, including DKD. The aberrant DNA methylation pattern at CpGs sites within several genes, such as mTOR, RPTOR, IRS2, GRK5, SLC27A3, LCAT, and SLC1A5, associated with the accompanying risk factors exacerbate the DKD progression. Although drugs such as azacytidine and decitabine have been approved to target DNA methylation for diseases such as hematological malignancies, none have been approved for the treatment of DKD. More importantly, no DNA hypomethylation-targeting drugs have been approved for any disease conditions. Understanding the alteration in DNA methylation and its association with the disease risk factors is essential to target DKD effectively. This review has discussed the abnormal DNA methylation pattern and the kidney tissue-specific expression of critical genes involved in DKD onset and progression. Moreover, we also discuss the new possible therapeutic approach that can be exploited for treating DNA methylation aberrancy in a site-specific manner against DKD.

Influence of renal function on the ability of TyG Index to predict all-cause mortality

BACKGROUND

The association between triglyceride-glucose (TyG) index and poor prognosis remains controversial. Whether renal function status affects the ability of the TyG index to predict poor prognosis has not yet been elucidated and merits further studies.

METHODS

This retrospective cohort study included 22,031 participants from communities in the U.S. By juxtaposing the TyG categories with the estimated glomerular filtration rate (eGFR, either < 60 mL/min/1.73m2 or ≥ 60 mL/min/1.73m2), participants were categorized into four distinct groups: (1) TyG_L/eGFR_H; (2) TyG_H/eGFR_H; (3) TyG_L/eGFR_L; and (4) TyG_H/eGFR_L. The endpoint was the all-cause mortality rate. Standard Kaplan-Meier plots were constructed and multifactor Cox regression analyses were carried out and restricted cubic spline regression analysis was utilized to assess the association between death and the TyG index for different renal function statuses.

RESULTS

No statistical differences were found in the TyG groups in participants with normal renal function after adjustment for all covariates (P = 0.070). However, in the high TyG index group with renal insufficiency, the risk of all-cause mortality rates was reduced by 18%. (HR, 0.82; CI, 0.69-0.98). The TyG index (high vs. low) and renal function (eGFR < 60 vs. eGFR ≥ 60) had statistically significant interactions with death (P < 0.001). When all covariates were adjusted, the risk of mortality for the TyG_L combined with eGFR_L group was 56% higher than that for the TyG_L combined with eGFR_H group (HR, 1.56; CI, 1.33-1.82). In the renal insufficiency population, a nonlinear relationship was observed between mortality and the TyG index, albeit with a differing pattern (P for nonlinearity < 0.001).

CONCLUSIONS

While it has been known that TyG index was a prognosis marker of CVD, this research highlights that higher TyG index was associated with higher all-cause mortality rates for all participants. Furthermore, renal function status significantly moderates the effect of the TyG index on all-cause mortality in community-dwelling adults.

Insulin and the kidneys: a contemporary view on the molecular basis

Insulin is a hormone that is composed of 51 amino acids and structurally organized as a hexamer comprising three heterodimers. Insulin is the central hormone involved in the control of glucose and lipid metabolism, aiding in processes such as body homeostasis and cell growth. Insulin is synthesized as a large preprohormone and has a leader sequence or signal peptide that appears to be responsible for transport to the endoplasmic reticulum membranes. The interaction of insulin with the kidneys is a dynamic and multicenter process, as it acts in multiple sites throughout the nephron. Insulin acts on a range of tissues, from the glomerulus to the renal tubule, by modulating different functions such as glomerular filtration, gluconeogenesis, natriuresis, glucose uptake, regulation of ion transport, and the prevention of apoptosis. On the other hand, there is sufficient evidence showing the insulin receptor's involvement in renal functions and its responsibility for the regulation of glucose homeostasis, which enables us to understand its contribution to the insulin resistance phenomenon and its association with the progression of diabetic kidney disease.

Renal insulin resistance in type 2 diabetes mellitus and progression of chronic kidney disease: potential pathogenic mechanisms

INTRODUCTION

A bidirectional association exists between insulin resistance (IR) and chronic kidney disease (CKD) in Type 2 Diabetes Mellitus (T2DM). Baseline measures of IR are predictive of CKD progression, and uremia in progressive CKD is itself, in turn, associated with a worsening of IR. Pre-clinical research reveals that intrinsic IR in glomerular podocytes and the renal tubule may serve as a pathogenic driver of CKD in T2DM.

AREAS COVERED

The present manuscript takes as its point of departure, the recently identified prognostic utility of severe insulin resistance as a predictor of CKD in T2DM. Findings from a series of studies describing the association of IR with pathological alterations in both established, and less commonly assessed dynamic measures of renal impairment are discussed. Drawing upon the pre-clinical mechanistic evidence base, the cellular and molecular basis of intrinsic renal IR as a promoter of CKD is considered.

EXPERT OPINION

Measurement of insulin sensitivity may add value to profiling of renal risk in T2DM. Rational selection of therapeutic strategies targeting the enhancement of insulin sensitivity merits special attention regarding the personalized management of CKD in insulin resistance predominant T2DM.

Soluble Insulin Receptor Levels in Plasma, Exosomes, and Urine and Its Association With HIV-Associated Neurocognitive Disorders

Background

HIV-associated neurocognitive disorders (HAND) are one of the HIV-associated comorbidities affecting 20-50% of the people with HIV (PWH) infection. We found that the soluble insulin receptor (sIR) levels in plasma and cerebrospinal fluid (CSF) were significantly higher in HIV-infected women. The mechanism of sIR release into the plasma remains unknown, but the detection of the sIR in exosomes may uncover novel mechanisms of sIR secretion from HIV-infected cells and its contribution to HIV disease progression and HAND development. Quantification of sIR in urine may represent a less invasive and more accessible diagnostic tool. Our objective was to quantify sIR levels in plasma, plasma-derived exosomes, and urine, and evaluate their association with HAND and renal function.

Methods

We measured full-length sIR in the plasma and urine of 38 controls and 76 HIV-infected women by ELISA, and sIR, HIV-1 Tat, and reactive oxygen species (ROS) in exosomes by flow cytometry.

Results

Plasma and exosomes with sIR were significantly higher in HIV-infected women when compared with controls and HAND. Exosomal sIR positively correlated with exosomal ROS and exosomal HIV-1 Tat in HIV-infected women. Exosomal ROS was significantly higher in HIV-infected women with more symptomatic cognitive impairment. Plasma-derived exosomes exhibited significantly higher levels of astrocyte (GFAP) and neuronal (L1CAM) markers in HIV-infected women, confirming the presence of circulating CNS-derived exosomes in the blood of HIV-infected women. Urine sIR positively correlated with eGFR in controls, but not in HIV-infected women, regardless there was no significant difference in renal function as determined by the estimated glomerular filtration rate (eGFR, p = 0.762). In HIV-infected women, higher plasma sIR correlated with lower urine sIR that could suggest sIR retention in blood or decreased renal filtration.

Discussion

Higher plasma sIR levels and their correlation with ROS in plasma-derived exosomes with HAND suggest a combined role of metabolic disturbances, oxidative stress, exosome release, and cognitive decline. Communication between CNS and periphery is compromised in PWH, thus plasma-derived exosomes may shed light on disrupted cellular mechanisms in the brain of PWH. High plasma and low urine sIR levels could suggest sIR retention in blood or decreased renal filtration.

Insulin Resistance and Vitamin D Deficiency: A Link Beyond the Appearances

Vitamin D is a steroid hormone that plays a key role in the regulation of body homeostasis, including cardiovascular function. Although the chronic deficiency of vitamin D is associated with cardiovascular risk factors, as well as with an adverse prognosis, randomized controlled trials have failed in demonstrating that dietary vitamin D supplementation could ameliorate the prognosis of patients with cardiovascular diseases, and suggested that vitamin D deficiency is the expression of the effects of other determinants of cardiovascular risk. Thus, the supplementation of vitamin D is not sufficient to improve the cardiovascular risk profile and prognosis. Insulin resistance is a complex phenomenon that plays a key role in the pathogenesis of conventional cardiovascular risk factors. Interestingly, defects of vitamin D and insulin resistance have a superimposable epidemiological distribution. According to the common view, Insulin resistance is considered the direct or indirect consequence of vitamin D deficiency. However, it is also reasonable to speculate that the deficit or the impaired action of vitamin D, in some circumstances, could be the result of the same pathogenic mechanisms responsible of insulin resistance development. In this case, vitamin D deficiency could be considered an epiphenomenon of insulin resistance. Insulin resistance is a reversible condition, being possibly ameliorated by physical activity and hypocaloric diets. Notably, both physical exercise and energy-restricted dietary regimens are associated with an increase of vitamin D levels. These findings indicate that improving insulin resistance condition is a necessary step to ameliorate vitamin D supplementation-based strategies in cardiovascular prevention.

OUP accepted manuscript

Background

In living kidney transplantation there are two different individuals, a healthy donor and a renal transplant recipient. This is an excellent human model to study factors that influence kidney function in the context of reduced renal mass and the adaptation of two comparable kidneys to different metabolic demands.

Methods

We analyzed the changes in measured glomerular filtration rate (GFR, iohexol) from pretransplantation to 12 months after transplantation in 30 donor–recipient pairs. Each donor was compared with his/her recipient. We defined a priori three different groups based on GFR differences at 12 months: donor > recipient (Group A; 78 ± 8 versus 57 ± 8 mL/min), donor < recipient (Group B; 65 ± 11 versus 79 ± 11 mL/min) and donor ≈ recipient (Group C; 66 ± 7 versus 67 ± 7 mL/min). Other factors like donor/recipient mismatches in body mass index (BMI), surface area and gender were evaluated.

Results

In Group A donors were mostly male and recipients were female (75% each). Donors had a higher baseline weight than their recipients. During follow-up, weight remained stable in donors but increased 7% in recipients. In Group B donors were mostly female (60%) and recipients male. At baseline, donors had a lower weight than recipients. At 12 months, weight was stable in donors but increased in recipients. In Group C donors were mostly (75%) female and recipients male. At baseline, donors had a higher BMI than their recipients. At 12 months, BMI was stable in donors but increased 14% in recipients. In multivariable analysis, higher GFR at 12 months was associated with higher baseline weight and GFR in donors and with male gender and higher baseline weight in recipients.

Conclusions

Kidneys from living donors are more ‘plastic’ than originally thought and respond to metabolic demands and weight changes of their new host. These changes should be taken into account when assessing GFR outcomes in this population.

Internal state effects on behavioral shifts in freely behaving praying mantises (Tenodera sinensis)

How we interact with our environment largely depends on both the external cues presented by our surroundings and the internal state from within. Internal states are the ever-changing physiological conditions that communicate the immediate survival needs and motivate the animal to behaviorally fulfill them. Satiety level constitutes such a state, and therefore has a dynamic influence on the output behaviors of an animal. In predatory insects like the praying mantis, hunting tactics, grooming, and mating have been shown to change hierarchical organization of behaviors depending on satiety. Here, we analyze behavior sequences of freely hunting praying mantises (Tenodera sinensis) to explore potential differences in sequential patterning of behavior as a correlate of satiety. First, our data supports previous work that showed starved praying mantises were not just more often attentive to prey, but also more often attentive to further prey. This was indicated by the increased time fraction spent in attentive bouts such as prey monitoring, head turns (to track prey), translations (closing the distance to the prey), and more strike attempts. With increasing satiety, praying mantises showed reduced time in these behaviors and exhibited them primarily towards close-proximity prey. Furthermore, our data demonstrates that during states of starvation, the praying mantis exhibits a stereotyped pattern of behavior that is highly motivated by prey capture. As satiety increased, the sequenced behaviors became more variable, indicating a shift away from the necessity of prey capture to more fluid presentations of behavior assembly.

Obesity and metabolic syndrome induce hyperfiltration, glomerulomegaly, and albuminuria in obese ovariectomized female mice and obese male mice

OBJECTIVE

Obese patients with metabolic syndrome have a high risk of chronic kidney disease. The prevalence of obesity, metabolic syndrome, and insulin resistance increase in women after menopause, as does the risk of chronic kidney disease. This may indicate an interaction between obesity, metabolic syndrome, and menopause in the induction of renal damage. However, the pathogenesis of kidney disease in postmenopausal obese women is poorly understood.

METHODS

We investigated the interaction of an obesogenic diet and menopause on renal dysfunction in ovariectomized and non-ovariectomized lean (n = 8 and 17) and obese (n = 12 and 20) female mice. Obese (n = 12) and lean (n = 10) male mice were also studied. Glucose metabolism, insulin resistance, and kidney function were evaluated with gold standards procedures. Changes in kidney histology and lipid deposition were analyzed. Females had a lower number of glomeruli than males at baseline.

RESULTS

Only female ovariectomized obese animals developed insulin resistance, hyperglycemia, and kidney damage, evidenced as glomerulomegaly, glomerular hyperfiltration, and increased urinary albumin excretion, despite a similar increase in weight than obese non-ovariectomized female mice. Male obese mice developed hyperglycemia, insulin resistance, and hyperfiltration without major renal histological changes. Males on high fat diet showed higher renal lipid content and females on high fat diet (ovariectomized or non-ovariectomized) showed higher total cholesterol content than males.

CONCLUSIONS

In mice, there is a clear interplay between obesity, metabolic syndrome, and menopause in the induction of kidney damage.

Insulin resistance in cardiovascular disease, uremia, and peritoneal dialysis

Diabetic nephropathy is highly correlated with the occurrence of other complications of type 1 diabetes (T1D) and type 2 diabetes (T2D) mellitus; for example, hypertension with cardiovascular disease (CVD) being the most frequent cause of death in patients with end-stage renal disease and undergoing renal dialysis. Hyperglycemia and insulin resistance (IR) are responsible for the micro- and macrovascular complications of diabetes through different mechanisms. In particular, IR plays a key role in the etiology of atherosclerosis in both diabetic and non-diabetic patients. IR - exacerbated by organ-level selectivity - is more important than glycemic control per se in determining cardiovascular outcomes. This may be exacerbated by the fact that IR is organ and pathway specific due to the only selective loss of sensitivity to insulin action of specific pathways/processes. Therefore, it is counterintuitive that the use of peritoneal dialysis (PD) in (frequently) diabetic renal disease patients should involve their exposure to high daily doses of glucose peritoneally. In view of the controversy about the causal association between glucose load and CVD in PD patients, we discuss the role that selective IR may play in the progression of CVD in diabetic renal end-stage patients. In discussing these associations, we propose that reducing glucose exposure in PD solutions may be beneficial especially if coupled with strategies that address IR directly, and the avoidance of excessive use of insulin treatment in T2D.

The effect of hypothyroidism on referential background metabolic activity on 18F-FDG PET/CT

Background

Background uptake activity is used as a reference to assess treatment response by positron emission tomography-computed tomography (PET/CT) with 2-deoxy-2-[F-18]fluoro- D-glucose (¹⁸F-FDG). Prior studies have reported decreased liver and increased muscle ¹⁸F-FDG uptake in patients with hyperthyroidism. We hypothesized that hyperthyroidism and hypothyroidism might have inverse effects on ¹⁸F-FDG uptake on PET/CT.

Methods

We recruited 36 patients with hypothyroidism and 36 age and gender-matched euthyroid participants. We recorded patient factors and background mean standardized uptake values normalized by lean body mass from the aortic blood pool, liver, and muscle. We compared the patient factors and background standardized uptake values normalized by lean body mass between hypothyroidism patients and the controls. We performed a multivariate analysis to determine the best predictors of the 3 different background standardized uptake values normalized by lean body mass.

Results

Patients with hypothyroidism had higher liver standardized uptake values normalized by lean body mass (1.77±0.33 vs. 1.58±0.26, P=0.009) and aortic blood-pool standardized uptake values normalized by lean body mass (1.21±0.22 vs. 1.11±0.20, P=0.040) than the controls. In contrast, the muscle standardized uptake value normalized by lean body mass (0.50±0.09 vs. 0.54±0.09, P=0.044) of the patients with hypothyroidism was lower than that of the controls. The serum level of thyroid-stimulating hormone was an independent predictor of liver standardized uptake values normalized by lean body mass (β=0.356, P<0.001) and blood-pool standardized uptake values normalized by lean body mass (β=0.288, P=0.001). The serum level of free triiodothyronine was an independent predictor of muscle standardized uptake values normalized by lean body mass (β=0.310, P=0.002).

Conclusions

PET/CT scans showed that hypothyroidism patients had increased liver and blood-pool ¹⁸F-FDG uptake and decreased skeletal muscle ¹⁸F-FDG uptake compared with euthyroid individuals. These alterations should be noted when a metabolic response to cancer treatment on PET/CT is determined.

Role of Insulin in Health and Disease: An Update

Insulin is a polypeptide hormone mainly secreted by β cells in the islets of Langerhans of the pancreas. The hormone potentially coordinates with glucagon to modulate blood glucose levels; insulin acts via an anabolic pathway, while glucagon performs catabolic functions. Insulin regulates glucose levels in the bloodstream and induces glucose storage in the liver, muscles, and adipose tissue, resulting in overall weight gain. The modulation of a wide range of physiological processes by insulin makes its synthesis and levels critical in the onset and progression of several chronic diseases. Although clinical and basic research has made significant progress in understanding the role of insulin in several pathophysiological processes, many aspects of these functions have yet to be elucidated. This review provides an update on insulin secretion and regulation, and its physiological roles and functions in different organs and cells, and implications to overall health. We cast light on recent advances in insulin-signaling targeted therapies, the protective effects of insulin signaling activators against disease, and recommendations and directions for future research.

Novel regulation of renal gluconeogenesis by Atp6ap2 in response to high fat diet via PGC1-α/AKT-1 pathway

Recent studies suggested that renal gluconeogenesis is substantially stimulated in the kidney in presence of obesity. However, the mechanisms responsible for such stimulation are not well understood. Recently, our laboratory demonstrated that mice fed high fat diet (HFD) exhibited increase in renal Atp6ap2 [also known as (Pro)renin receptor] expression. We hypothesized that HFD upregulates renal gluconeogenesis via Atp6ap2-PGC-1α and AKT pathway. Using real-time polymerase chain reaction, western blot analysis and immunostaining, we evaluated renal expression of the Atp6ap2 and renal gluconeogenic enzymes, PEPCK and G6Pase, in wild type and inducible nephron specific Atp6ap2 knockout mice fed normal diet (ND, 12 kcal% fat) or a high-fat diet (HFD, 45 kcal% fat) for 8 weeks. Compared with ND, HFD mice had significantly higher body weight (23%) (P < 0.05), renal mRNA and protein expression of Atp6ap2 (39 and 35%), PEPCK (44 and 125%) and G6Pase (39 and 44%) respectively. In addition, compared to ND, HFD mice had increased renal protein expression of PGC-1α by 32% (P < 0.05) and downregulated AKT by 33% (P < 0.05) respectively in renal cortex. Atp6ap2-KO abrogated these changes in the mice fed HFD. In conclusion, we identified novel regulation of renal gluconeogenesis by Atp6ap2 in response to high fat diet via PGC1-α/AKT-1 pathway.

High sucrose diet induces morphological, structural and functional impairments in the renal tubules of Drosophila melanogaster: A model for studying type-2 diabetes mediated renal tubular dysfunction

Continuous feeding of high dietary sugar is strongly associated with type 2 diabetes (T2D) and its secondary complications. Diabetic nephropathy (DN) is a major secondary complication that leads to glomerular and renal tubular dysfunction. The present study is aimed to investigate the effects of chronic exposure of high sugar diet (HSD) on renal tubules. Malpighian tubules (MTs), a renal organ of Drosophila, were used as a model in the study. Feeding of HSD develops T2D condition in Drosophila. The MTs showed structural abnormalities in 20 days of HSD fed flies. Impaired insulin signaling, oxidative stress, enhanced levels of AGE-RAGE and induction of apoptosis were observed in the MTs of these flies. Further, altered expression of transporters, enhanced uric acid level and reduced fluid secretion rate confirmed the impaired function of MTs in these flies. RNA-seq and RT-PCR analyses in the MTs of HSD fed-and control-flies revealed the altered expression of candidate genes that regulate several important pathways including extracellular matrix (ECM), advanced glycation end products-receptor for advanced glycation end products (AGE-RAGE), transforming growth factor β (TGF-β), galactose, starch and sucrose metabolism that are well known mediators of renal tubular dysfunction in DN patients. Disruption of insulin signaling in the MTs also causes renal tubular dysfunction similar to HSD fed flies. Overall, the study suggests that phenotypes observed in the MTs of HSD fed flies recapitulate several hallmarks of renal tubular dysfunction in DN patients. Therefore, we conclude that MTs of HSD fed flies may be used for deciphering the underlying mechanisms of T2D mediated renal tubular dysfunction.

The Interaction of the Endogenous Hydrogen Sulfide and Oxytocin Systems in Fluid Regulation and the Cardiovascular System

The purpose of this review is to explore the parallel roles and interaction of hydrogen sulfide (H2S) and oxytocin (OT) in cardiovascular regulation and fluid homeostasis. Their interaction has been recently reported to be relevant during physical and psychological trauma. However, literature reports on H2S in physical trauma and OT in psychological trauma are abundant, whereas available information regarding H2S in psychological trauma and OT in physical trauma is much more limited. This review summarizes recent direct and indirect evidence of the interaction of the two systems and their convergence in downstream nitric oxide-dependent signaling pathways during various types of trauma, in an effort to better understand biological correlates of psychosomatic interdependencies.

Establishment of Rat Model of Insulin Resistance Exposed to Chronic Renal Allograft Dysfunction

BACKGROUND

The main cause of chronic renal allograft dysfunction (CRAD) still remains unclear. Insulin resistance (IR) may be a potential inducement, but there is insufficient evidence about this association. We aimed to establish a rat model of CRAD complicated with IR and to explore the function and pathologic changes of the renal allograft induced by IR.

METHODS

F344-to-Lewis rats of CRAD were fed a high-fat diet to induce IR. They were divided into 3 groups: IR (CRAD+IR), CRAD, and control (CTL). Serum levels of blood urea nitrogen (BUN) and serum creatinine (Scr) were measured to evaluate the renal function. The Homeostasis Model Assessment (HOMA)-IR index was detected by comparing the values of fasting serum insulin levels (FINS) with fasting blood glucose levels (FBG). The pathologic analysis was conducted by the degree of renal lesions including glomerular lesions, renal tubular lesions, hemorrhage, inflammatory cell infiltration, fibrillation, and hyperplasia of the renal interstitium.

RESULTS

In the second, third, and fourth month after surgery, serum levels of Scr and BUN in the IR group were reduced more than those in the CRAD group, while they were both higher compared to the CTL group, suggesting that renal function in the CRAD group was declined. The HOMA-IR in the IR group was greater than that in the CRAD and CTL groups, showing that simple high-fat diet feeding significantly and steadily increased FINS and FBG in CRAD complicated with IR rats. Pathologic changes indicated that the CRAD rat model was successfully constructed and was still in the early-middle stages of renal lesions 4 months after surgery, yet IR presented a significant effect on CRAD.

CONCLUSION

These results indicate that the stable CRAD complicated with IR rat model can be established through a high-fat diet in CRAD rats in 4 months, and IR could be an influencing factor.

Sex-specific associations of insulin resistance with chronic kidney disease and kidney function: a bi-directional Mendelian randomisation study

AIMS/HYPOTHESIS

Reasons for the sexual disparity in chronic kidney disease (CKD) are unclear. To provide insight we contextualised these differences within evolutionary biology, and explored sex-specific effects of insulin resistance because it may have sex-specific effects on the reproductive axis. Impaired kidney function may also cause insulin resistance. We assessed these possibilities using bi-directional, sex-specific, two-sample Mendelian randomisation (MR).

METHODS

Given that fasting insulin, fasting glucose and HbA_1c are related, we used MR-Bayesian model averaging (MR-BMA) to identify the best-fitting model and most influential exposure. Genetic associations with glycaemic traits were obtained from genome-wide association studies (GWAS) in Europeans without diabetes (n = 108,557 for fasting insulin, as a proxy for insulin resistance, and for fasting glucose, n = 123,665 for HbA_1c in the Meta-Analyses of Glucose and Insulin-related traits Consortium [MAGIC]), and applied to GWAS of 480,698 Europeans for overall associations with CKD (cases n = 41,395) and eGFR. We also used sex-specific individual information in white British (179,917 men, 6016 CKD cases; 212,079 women, 5958 CKD cases) from the UK Biobank. Univariable or multivariable MR was used to assess the role of glycaemic trait(s) selected by MR-BMA in CKD and kidney function. Genetic variants predicting eGFR were used to assess the role of kidney function in the most influential exposure(s).

RESULTS

Fasting insulin was selected as the most likely exposure by both overall and sex-specific MR-BMA. It increased CKD in men (OR 7.23 per pmol/l higher fasting insulin [95% CI 2.46, 21.2]) but not in women (OR 1.05 [95% CI 0.21, 5.21]), and reduced eGFR in men (-0.04 [95% CI -0.07, -0.01]) but not in women (0.01 [95% CI -0.02, 0.03]). Genetically predicted eGFR was unrelated to fasting insulin.

CONCLUSIONS/INTERPRETATION

Genetically predicted fasting insulin was sex-specifically associated with CKD and unhealthier kidney function but was not affected by kidney function. Graphical abstract.

The roles of melatonin on kidney injury in obese and diabetic conditions

Obesity is a common and complex health problem worldwide and can induce the development of Type 2 diabetes. Chronic kidney disease (CKD) is a complication occurring as a result of obesity and diabetic conditions that lead to an increased mortality rate. There are several mechanisms and pathways contributing to kidney injury in obese and diabetic conditions. The expansion of adipocytes triggers proinflammatory cytokines release into blood circulation and bind with the receptors at the cell membranes of renal tissues leading to kidney injury. Obesity-mediated inflammation, oxidative stress, apoptosis, and mitochondrial dysfunction are the important causes and progression of CKD. Melatonin (N-acetyl-5-methoxytryptamine) is a neuronal hormone that is synthesized by the pineal gland and plays an essential role in regulating several physiological functions in the human body. Moreover, melatonin has pleiotropic effects such as antioxidant, anti-inflammation, antiapoptosis. In this review, the relationship between obesity, diabetic condition, and kidney injury and the renoprotective effect of melatonin in obese and diabetic conditions from in vitro and in vivo studies have been summarized and discussed.

Postprandial effects on electrolyte homeostasis in the kidney

Insulin is known to be an important regulator of a number of different channels and transporters in the kidney, but its role in the kidney to prevent Na⁺ and volume loss during the osmotic load after a meal has only recently been validated. With increasing numbers of people suffering from diabetes and hypertension, furthering our understanding of insulin signaling and renal Na⁺ handling in both normal and diseased states is essential for improving patient treatments and outcomes. The present review is focused on postprandial effects on Na⁺ reabsorption in the kidney and the role of the epithelial Na⁺ channels as an important channel contributing to insulin-mediated Na⁺ reclamation.