Leptin therapy improves insulin-deficient type 1 diabetes by CNS-dependent mechanisms in mice. Proc Natl Acad Sci U S A. 2010;107:17391-17396. [PMID: 20855609 DOI: 10.1073/pnas.1008025107]

Diabetes-induced male infertility: potential mechanisms and treatment options

Male infertility is a physiological phenomenon in which a man is unable to impregnate a fertile woman during a 12-month period of continuous, unprotected sexual intercourse. A growing body of clinical and epidemiological evidence indicates that the increasing incidence of male reproductive problems, especially infertility, shows a very similar trend to the incidence of diabetes within the same age range. In addition, a large number of previous in vivo and in vitro experiments have also suggested that the complex pathophysiological changes caused by diabetes may induce male infertility in multiple aspects, including hypothalamic-pituitary-gonadal axis dysfunction, spermatogenesis and maturation disorders, testicular interstitial cell damage erectile dysfunction. Based on the above related mechanisms, a large number of studies have focused on the potential therapeutic association between diabetes progression and infertility in patients with diabetes and infertility, providing important clues for the treatment of this population. In this paper, we summarized the research results of the effects of diabetes on male reproductive function in recent 5 years, elaborated the potential pathophysiological mechanisms of male infertility induced by diabetes, and reviewed and prospected the therapeutic measures.

Systemic Glucose Regulation by a Hindbrain Inhibitory Circuit in a Mouse Model of Type 1 Diabetes

INTRODUCTION

Previous work showed that increasing the electrical activity of inhibitory neurons in the dorsal vagal complex (DVC) is sufficient to increase whole-body glucose concentration in normoglycemic mice. Here we tested the hypothesis that deactivating GABAergic neurons in the dorsal hindbrain of hyperglycemic mice decreases synaptic inhibition of parasympathetic motor neurons in the dorsal motor nucleus of the vagus (DMV) and reduces systemic glucose levels.

METHODS

Chemogenetic activation or inactivation of GABAergic neurons in the nucleus tractus solitarius (NTS) was used to assess effects of modulating parasympathetic output on blood glucose concentration in normoglycemic and hyperglycemic mice. Patch-clamp electrophysiology in vitro was used to assess cellular effects of chemogenetic manipulation of NTS GABA neurons.

RESULTS

Chemogenetic activation of GABAergic NTS neurons in normoglycemic mice increased their action potential firing, resulting in increased inhibitory synaptic input to DMV motor neurons and elevated blood glucose concentration. Deactivation of GABAergic DVC neurons in normoglycemic mice altered their electrical activity but did not alter systemic glucose levels. Conversely, stimulation of GABAergic DVC neurons in mice that were hyperglycemic subsequent to treatment with streptozotocin changed their electrical activity but did not alter whole-body glucose concentration, while deactivation of this inhibitory circuit significantly decreased circulating glucose concentration. Peripheral administration of a brain impermeant muscarinic acetylcholine receptor antagonist abolished these effects.

CONCLUSION

Disinhibiting vagal motor neurons decreases hyperglycemia in a mouse model of type 1 diabetes. This inhibitory brainstem circuit emerges as a key parasympathetic regulator of whole-body glucose homeostasis that undergoes functional plasticity in hyperglycemic conditions.

S100A9 exerts insulin-independent antidiabetic and anti-inflammatory effects

Type 1 diabetes mellitus (T1DM) is characterized by insulin deficiency leading to hyperglycemia and several metabolic defects. Insulin therapy remains the cornerstone of T1DM management, yet it increases the risk of life-threatening hypoglycemia and the development of major comorbidities. Here, we report an insulin signaling-independent pathway able to improve glycemic control in T1DM rodents. Co-treatment with recombinant S100 calcium-binding protein A9 (S100A9) enabled increased adherence to glycemic targets with half as much insulin and without causing hypoglycemia. Mechanistically, we demonstrate that the hyperglycemia-suppressing action of S100A9 is due to a Toll-like receptor 4-dependent increase in glucose uptake in specific skeletal muscles (i.e., soleus and diaphragm). In addition, we found that T1DM mice have abnormal systemic inflammation, which is resolved by S100A9 therapy alone (or in combination with low insulin), hence uncovering a potent anti-inflammatory action of S100A9 in T1DM. In summary, our findings reveal the S100A9-TLR4 skeletal muscle axis as a promising therapeutic target for improving T1DM treatment.

VMHdm/cSF-1 neuronal circuits regulate skeletal muscle PGC1-α via the sympathoadrenal drive

OBJECTIVE

To adapt to metabolically challenging environments, the central nervous system (CNS) orchestrates metabolism of peripheral organs including skeletal muscle. The organ-communication between the CNS and skeletal muscle has been investigated, yet our understanding of the neuronal pathway from the CNS to skeletal muscle is still limited. Neurons in the dorsomedial and central parts of the ventromedial hypothalamic nucleus (VMHdm/c) expressing steroidogenic factor-1 (VMHdm/cSF-1 neurons) are key for metabolic adaptations to exercise, including increased basal metabolic rate and skeletal muscle mass in mice. However, the mechanisms by which VMHdm/cSF-1 neurons regulate skeletal muscle function remain unclear. Here, we show that VMHdm/cSF-1 neurons increase the sympathoadrenal activity and regulate skeletal muscle peroxisome proliferator-activated receptor gamma coactivator 1 alpha (PGC-1α) in mice via multiple downstream nodes.

METHODS

Optogenetics was used to specifically manipulate VMHdm/cSF-1 neurons combined with genetically-engineered mice and surgical manipulation of the sympathoadrenal activity.

RESULTS

Optogenetic activation of VMHdm/cSF-1 neurons dramatically elevates mRNA levels of skeletal muscle Pgc-1α, which regulates a spectrum of skeletal muscle function including protein synthesis and metabolism. Mechanistically, the sympathoadrenal drive coupled with β2 adrenergic receptor (β2AdR) is essential for VMHdm/cSF-1 neurons-mediated increases in skeletal muscle PGC1-α. Specifically, both adrenalectomy and β2AdR knockout block augmented skeletal muscle PGC1-α by VMHdm/cSF-1 neuronal activation. Optogenetic functional mapping reveals that downstream nodes of VMHdm/cSF-1 neurons are functionally redundant to increase circulating epinephrine and skeletal muscle PGC1-α.

CONCLUSIONS

Collectively, we propose that VMHdm/cSF-1 neurons-skeletal muscle pathway, VMHdm/cSF-1 neurons→multiple downstream nodes→the adrenal gland→skeletal muscle β2AdR, underlies augmented skeletal muscle function for metabolic adaptations.

The Interplay of Adipokines and Pancreatic Beta Cells in Metabolic Regulation and Diabetes

The interplay between adipokines and pancreatic beta cells, often referred to as the adipo-insular axis, plays a crucial role in regulating metabolic homeostasis. Adipokines are signaling molecules secreted by adipocytes that have profound effects on several physiological processes. Adipokines such as adiponectin, leptin, resistin, and visfatin influence the function of pancreatic beta cells. The reciprocal communication between adipocytes and beta cells is remarkable. Insulin secreted by beta cells affects adipose tissue metabolism, influencing lipid storage and lipolysis. Conversely, adipokines released from adipocytes can influence beta cell function and survival. Chronic obesity and insulin resistance can lead to the release of excess fatty acids and inflammatory molecules from the adipose tissue, contributing to beta cell dysfunction and apoptosis, which are key factors in developing type 2 diabetes. Understanding the complex interplay of the adipo-insular axis provides insights into the mechanisms underlying metabolic regulation and pathogenesis of metabolic disorders. By elucidating the molecular mediators involved in this interaction, new therapeutic targets and strategies may emerge to reduce the risk and progression of diseases, such as type 2 diabetes and its associated complications. This review summarizes the interactions between adipokines and pancreatic beta cells, and their roles in the pathogenesis of diabetes and metabolic diseases.

The Importance of Dietary Fiber for Metabolic Health

Dietary fiber are non-digestible carbohydrates that are diverse, have varied functions, and are acquired by consuming plant-based foods. Some forms of fiber are digested by the gut microbiota and produce bioactive metabolites called short chain fatty acids-butyrate, acetate, and propionate. Dietary fiber is able to alter human physiology through multiple mechanisms that can result in health benefits. Unfortunately, nearly 19 out of 20 Americans do not consume the minimum recommended amount of fiber each day. This bears profound relevance to public health because at least six of the ten leading causes of death are potentially preventable or clinically improved through dietary means. Additionally, these same conditions share a common underlying pathophysiology-metabolic dysfunction. This can manifest as abdominal obesity, high blood pressure, insulin resistance, dyslipidemia, or collectively as metabolic syndrome. In this review, we will assess the evidence that consumption of dietary fiber undermines these forms of metabolic dysfunction, examine the mechanism of action for these physiologic effects, and consider the potential for dietary fiber to improve human health on a public health level by simply encouraging our patients to consume more plant-based foods in abundance and diversity.

The role of short-chain fatty acids produced by gut microbiota in the regulation of pre-eclampsia onset

Background

Preeclampsia (PE) is a common pregnancy-related disorder characterized by disrupted maternal-fetal immune tolerance, involving diffuse inflammatory responses and vascular endothelial damage. Alterations in the gut microbiota (GM) during pregnancy can affect intestinal barrier function and immune balance.

Aims and purpose

This comprehensive review aims to investigate the potential role of short-chain fatty acids (SCFAs), essential metabolites produced by the GM, in the development of PE. The purpose is to examine their impact on colonic peripheral regulatory T (Treg) cells, the pathogenic potential of antigen-specific helper T (Th) cells, and the inflammatory pathways associated with immune homeostasis.

Key insights

An increasing body of evidence suggests that dysbiosis in the GM can lead to alterations in SCFA levels, which may significantly contribute to the development of PE. SCFAs enhance the number and function of colonic Treg cells, mitigate the pathogenic potential of GM-specific Th cells, and inhibit inflammatory progression, thereby maintaining immune homeostasis. These insights highlight the potential significance of GM dysregulation and SCFAs produced by GM in the pathogenesis of PE. While the exact causes of PE remain elusive, and definitive clinical treatments are lacking, the GM and SCFAs present promising avenues for future clinical applications related to PE, offering a novel approach for prophylaxis and therapy.

Association between leptin and NAFLD: a two-sample Mendelian randomization study

BACKGROUND

The etiology of nonalcoholic fatty liver disease (NAFLD) involves a complex interaction of genetic and environmental factors. Previous observational studies have revealed that higher leptin levels are related to a lower risk of developing NAFLD, but the causative association remains unknown. We intended to study the causal effect between leptin and NAFLD using the Mendelian randomization (MR) study.

METHODS

We performed a two-sample Mendelian randomization (TSMR) analysis using summary GWAS data from leptin (up to 50,321 individuals) and NAFLD (8,434 cases and 770,180 controls) in a European population. Instrumental variables (IVs) that satisfied the three core assumptions of Mendelian randomization were selected. The TSMR analysis was conducted using the inverse variance weighted (IVW) method, MR-Egger regression method, and weighted median (WM) method. To ensure the accuracy and stability of the study results, heterogeneity tests, multiple validity tests, and sensitivity analyses were conducted.

RESULTS

The findings of the TSMR correlation analysis between NAFLD and leptin were as follows: IVW method (odds ratio (OR) 0.6729; 95% confidence interval (95% CI) 0.4907-0.9235; P = 0.0142), WM method (OR 0.6549; 95% CI 0.4373-0.9806; P = 0.0399), and MR-Egger regression method (P = 0.6920). Additionally, the findings of the TSMR correlation analysis between NAFLD and circulating leptin levels adjusted for body mass index (BMI) were as follows: IVW method (OR 0.5876; 95% CI 0.3781-0.9134; P = 0.0181), WM method (OR 0.6074; 95% CI 0.4231-0.8721; P = 0.0069), and MR-Egger regression method (P = 0.8870). It has also been shown that higher levels of leptin are causally linked to a lower risk of developing NAFLD, suggesting that leptin may serve as a protective factor for NAFLD.

CONCLUSIONS

Using TSMR analysis and the GWAS database, we investigated the genetic relationship between elevated leptin levels and lowered risk of NAFLD in this study. However, further research is required to understand the underlying mechanisms.

Pectin mediates the mechanism of host blood glucose regulation through intestinal flora

Pectin is a complex polysaccharide found in plant cell walls and interlayers. As a food component, pectin is benefit for regulating intestinal flora. Metabolites of intestinal flora, including short-chain fatty acids (SCFAs), bile acids (BAs) and lipopolysaccharides (LPS), are involved in blood glucose regulation. SCFAs promote insulin synthesis through the intestine-GPCRs-derived pathway and hepatic adenosine 5'-monophosphate (AMP)-activated protein kinase (AMPK) pathway to promote hepatic glycogen synthesis. On the one hand, BAs stimulate intestinal L cells and pancreatic α cells to secrete Glucagon-like peptide-1 (GLP-1) and peptide YY (PYY) through receptors G protein-coupled receptor (TGR5) and farnesoid X receptor (FXR). On the other hand, BAs promote hepatic glycogen synthesis through AMPK pathway. LPS inhibits the release of inflammatory cytokines through Toll-like receptors (TLRs)-myeloid differentiation factor 88 (MYD88) pathway and mitogen-activated protein kinase (MAPK) pathway, thereby alleviating insulin resistance (IR). In brief, both SCFAs and BAs promote GLP-1 secretion through different pathways, employing strategies of increasing glucose consumption and decreasing glucose production to maintain normal glucose levels. Notably, pectin can also directly inhibit the release of inflammatory cytokines through the -TLRs-MYD88 pathway. These data provide valuable information for further elucidating the relationship between pectin-intestinal flora-glucose metabolism.

The sympathetic nervous system in the 21st century: Neuroimmune interactions in metabolic homeostasis and obesity

The sympathetic nervous system maintains metabolic homeostasis by orchestrating the activity of organs such as the pancreas, liver, and white and brown adipose tissues. From the first renderings by Thomas Willis to contemporary techniques for visualization, tracing, and functional probing of axonal arborizations within organs, our understanding of the sympathetic nervous system has started to grow beyond classical models. In the present review, we outline the evolution of these findings and provide updated neuroanatomical maps of sympathetic innervation. We offer an autonomic framework for the neuroendocrine loop of leptin action, and we discuss the role of immune cells in regulating sympathetic terminals and metabolism. We highlight potential anti-obesity therapeutic approaches that emerge from the modern appreciation of SNS as a neural network vis a vis the historical fear of sympathomimetic pharmacology, while shifting focus from post- to pre-synaptic targeting. Finally, we critically appraise the field and where it needs to go.

Action mechanism of hypoglycemic principle 9-(R)-HODE isolated from cortex lycii based on a metabolomics approach

The 9-(R)-HODE is an active compound isolated from cortex lycii that showed significant hypoglycemic effects in our previous in vitro study. In this study, 9-(R)-HODE’s in vivo hypoglycemic activity and effect on alleviating diabetic complications, together with its molecular mechanism, was investigated using a metabolomics approach. The monitored regulation on dynamic fasting blood glucose, postprandial glucose, body weight, biochemical parameters and histopathological analysis confirmed the hypoglycemic activity and attenuation effect, i.e., renal lesions, of 9-(R)-HODE. Subsequent metabolomic studies indicated that 9-(R)-HODE induced metabolomic alterations primarily by affecting the levels of amino acids, organic acids, alcohols and amines related to amino acid metabolism, glucose metabolism and energy metabolism. By mediating the related metabolism or single molecules related to insulin resistance, e.g., kynurenine, myo-inositol and the branched chain amino acids leucine, isoleucine and valine, 9-(R)-HODE achieved its therapeutic effect. Moreover, the mediation of kynurenine displayed a systematic effect on the liver, kidney, muscle, plasma and faeces. Lipidomic studies revealed that 9-(R)-HODE could reverse the lipid metabolism disorder in diabetic mice mainly by regulating phosphatidylinositols, lysophosphatidylcholines, lysophosphatidylcholines, phosphatidylserine, phosphatidylglycerols, lysophosphatidylglycerols and triglycerides in both tissues and plasma. Treatment with 9-(R)-HODE significantly modified the structure and composition of the gut microbiota. The SCFA-producing bacteria, including Rikenellaceae and Lactobacillaceae at the family level and Ruminiclostridium 6, Ruminococcaceae UCG 014, Mucispirillum, Lactobacillus, Alistipes and Roseburia at the genus level, were increased by 9-(R)-HODE treatment. These results were consistent with the increased SCFA levels in both the colon content and plasma of diabetic mice treated with 9-(R)-HODE. The tissue DESI‒MSI analysis strongly confirmed the validity of the metabolomics approach in illustrating the hypoglycemic and diabetic complications-alleviation effect of 9-(R)-HODE. The significant upregulation of liver glycogen in diabetic mice by 9-(R)-HODE treatment validated the interpretation of the metabolic pathways related to glycogen synthesis in the integrated pathway network. Altogether, 9-(R)-HODE has the potential to be further developed as a promising candidate for the treatment of diabetes.

Central and peripheral regulations mediated by short-chain fatty acids on energy homeostasis

The human gut microbiota influences obesity, insulin resistance, and the subsequent development of type 2 diabetes (T2D). The gut microbiota digests and ferments nutrients resulting in the production of short-chain fatty acids (SCFAs), which generate various beneficial metabolic effects on energy and glucose homeostasis. However, their roles in the central nervous system (CNS)-mediated outputs on the metabolism have only been minimally studied. Here, we explore what is known and future directions that may be worth exploring in this emerging area. Specifically, we searched studies or data in English by using PubMed, Google Scholar, and the Human Metabolome Database. Studies were filtered by time from 1978 to March 2022. As a result, 195 studies, 53 reviews, 1 website, and 1 book were included. One hundred and sixty-five of 195 studies describe the production and metabolism of SCFAs or the effects of SCFAs on energy homeostasis, glucose balance, and mental diseases through the gut-brain axis or directly by a central pathway. Thirty of 195 studies show that inappropriate metabolism and excessive of SCFAs are metabolically detrimental. Most studies suggest that SCFAs exert beneficial metabolic effects by acting as the energy substrate in the TCA cycle, regulating the hormones related to satiety regulation and insulin secretion, and modulating immune cells and microglia. These functions have been linked with AMPK signaling, GPCRs-dependent pathways, and inhibition of histone deacetylases (HDACs). However, the studies focusing on the central effects of SCFAs are still limited. The mechanisms by which central SCFAs regulate appetite, energy expenditure, and blood glucose during different physiological conditions warrant further investigation.

Construction of a double-responsive modified guar gum nanoparticles and its application in oral insulin administration

The use of intelligent insulin delivery systems has become more important for treating diabetes. In this study, a dual-responsive oral insulin delivery nanocarrier that responds to glucose and pH has been developed. First, the oleic acid hydrophobic modified guar gum (GG) was synthesized by the esterification reaction, and the γ-polyglutamic acid (γ-PGA) was coupled with GG by the amidation reaction. The obtained pH-responsive copolymer (γ-PGA-GG) was cross-linked by concanavalin A to obtain pH/glucose dual-responsive nanocarriers, and insulin was effectively loaded into the dual-responsive nanocarriers. The insulin-loaded nanoparticles can achieve effective pH and glucose responses, releasing insulin on demand. In vitro and in vivo studies demonstrated the dual-responsive nanoparticles can protect insulin against the pH changes in the digestive tract and deliver insulin into the body to exert a hypoglycemic effect. Moreover, the dual-responsive nanoparticles have significant potential to be employed for oral insulin delivery.

Hyperglycemia and reduced adiposity of streptozotocin-induced diabetic mice are not alleviated by oral benzylamine supplementation

BACKGROUND

Benzylamine (Bza) oral administration delays the onset of hyperglycemia in insulin-resistant db^-/- mice; a genetic model of obesity and type 2 diabetes.

AIM

To extend the antihyperglycemic properties of oral benzylamine to a model of insulin-deficient type 1 diabetes.

METHODS

Male Swiss mice were rendered diabetic by streptozotocin treatment (STZ) and divided in two groups: one received 0.5% Bza as drinking solution for 24 d (STZ Bza-drinking) while the other was drinking water ad libitum. Similar groups were constituted in age-matched, nondiabetic mice. Food intake, liquid intake, body weight gain and nonfasting blood glucose levels were followed during treatment. At the end of treatment, fasted glycemia, liver and white adipose tissue (WAT) mass were measured, while glucose uptake assays were performed in adipocytes.

RESULTS

STZ diabetic mice presented typical features of insulin-deficient diabetes: reduced body mass and increased blood glucose levels. These altered parameters were not normalized in the Bza-drinking group in spite of restored food and water intake. Bza consumption could not reverse the severe fat depot atrophy of STZ diabetic mice. In the nondiabetic mice, no difference was found between control and Bza-drinking mice for any parameter. In isolated adipocytes, hexose uptake was partially activated by 0.1 mmol/L Bza in a manner that was obliterated in vitro by the amine oxidase inhibitor phenelzine and that remained unchanged after Bza supplementation. Oxidation of 0.1 mmol/L Bza in WAT was lower in STZ diabetic than in normoglycemic mice.

CONCLUSION

Bza supplementation could not normalize the altered glucose handling of STZ diabetic mice with severe WAT atrophy. Consequently, its antidiabetic potential in obese and diabetic rodents does not apply to lipoatrophic type 1 diabetic mice.

The acromegaly lipodystrophy

Growth hormone (GH) and insulin-like growth factor 1 (IGF-1) are essential to normal growth, metabolism, and body composition, but in acromegaly, excesses of these hormones strikingly alter them. In recent years, the use of modern methodologies to assess body composition in patients with acromegaly has revealed novel aspects of the acromegaly phenotype. In particular, acromegaly presents a unique pattern of body composition changes in the setting of insulin resistance that we propose herein to be considered an acromegaly-specific lipodystrophy. The lipodystrophy, initiated by a distinctive GH-driven adipose tissue dysregulation, features insulin resistance in the setting of reduced visceral adipose tissue (VAT) mass and intra-hepatic lipid (IHL) but with lipid redistribution, resulting in ectopic lipid deposition in muscle. With recovery of the lipodystrophy, adipose tissue mass, especially that of VAT and IHL, rises, but insulin resistance is lessened. Abnormalities of adipose tissue adipokines may play a role in the disordered adipose tissue metabolism and insulin resistance of the lipodystrophy. The orexigenic hormone ghrelin and peptide Agouti-related peptide may also be affected by active acromegaly as well as variably by acromegaly therapies, which may contribute to the lipodystrophy. Understanding the pathophysiology of the lipodystrophy and how acromegaly therapies differentially reverse its features may be important to optimizing the long-term outcome for patients with this disease. This perspective describes evidence in support of this acromegaly lipodystrophy model and its relevance to acromegaly pathophysiology and the treatment of patients with acromegaly.

Protein Tyrosine Phosphatase 1B Deficiency Improves Glucose Homeostasis in Type 1 Diabetes Treated With Leptin

Leptin, a hormone secreted by adipocytes, exhibits therapeutic potential for the treatment of type 1 diabetes (T1D). Protein tyrosine phosphatase 1B (PTP1B) is a key enzyme that negatively regulates leptin receptor signaling. Here, the role of PTP1B in the treatment of T1D was investigated using PTP1B-deficient (knockout [KO]) mice and a PTP1B inhibitor. T1D wild-type (WT) mice induced by streptozotocin showed marked hyperglycemia compared with non-T1D WT mice. KO mice displayed significantly improved glucose metabolism equivalent to non-T1D WT mice, whereas peripheral or central administration of leptin partially improved glucose metabolism in T1D WT mice. Peripheral combination therapy of leptin and a PTP1B inhibitor in T1D WT mice improved glucose metabolism to the same level as non-T1D WT mice. Leptin was shown to act on the arcuate nucleus in the hypothalamus to suppress gluconeogenesis in liver and enhance glucose uptake in both brown adipose tissue and soleus muscle through the sympathetic nervous system. These effects were enhanced by PTP1B deficiency. Thus, treatment of T1D with leptin, PTP1B deficiency, or a PTP1B inhibitor was shown to enhance leptin activity in the hypothalamus to improve glucose metabolism. These findings suggest a potential alternative therapy for T1D.

Pancreatic Islets as a Target of Adipokines

Rising rates of obesity are intricately tied to the type 2 diabetes epidemic. The adipose tissues can play a central role in protection against or triggering metabolic diseases through the secretion of adipokines. Many adipokines may improve peripheral insulin sensitivity through a variety of mechanisms, thereby indirectly reducing the strain on beta cells and thus improving their viability and functionality. Such effects will not be the focus of this article. Rather, we will focus on adipocyte-secreted molecules that have a direct effect on pancreatic islets. By their nature, adipokines represent potential druggable targets that can reach the islets and improve beta-cell function or preserve beta cells in the face of metabolic stress. © 2022 American Physiological Society. Compr Physiol 12:1-27, 2022.

Leptin signaling and leptin resistance

With the prevalence of obesity and associated comorbidities, studies aimed at revealing mechanisms that regulate energy homeostasis have gained increasing interest. In 1994, the cloning of leptin was a milestone in metabolic research. As an adipocytokine, leptin governs food intake and energy homeostasis through leptin receptors (LepR) in the brain. The failure of increased leptin levels to suppress feeding and elevate energy expenditure is referred to as leptin resistance, which encompasses complex pathophysiological processes. Within the brain, LepR-expressing neurons are distributed in hypothalamus and other brain areas, and each population of the LepR-expressing neurons may mediate particular aspects of leptin effects. In LepR-expressing neurons, the binding of leptin to LepR initiates multiple signaling cascades including janus kinase (JAK)-signal transducers and activators of transcription (STAT) phosphatidylinositol 3-kinase (PI3K)-protein kinase B (AKT), extracellular regulated protein kinase (ERK), and AMP-activated protein kinase (AMPK) signaling, etc., mediating leptin actions. These findings place leptin at the intersection of metabolic and neuroendocrine regulations, and render leptin a key target for treating obesity and associated comorbidities. This review highlights the main discoveries that shaped the field of leptin for better understanding of the mechanism governing metabolic homeostasis, and guides the development of safe and effective interventions to treat obesity and associated diseases.

Hepatic non-parenchymal S100A9-TLR4-mTORC1 axis normalizes diabetic ketogenesis

Unrestrained ketogenesis leads to life-threatening ketoacidosis whose incidence is high in patients with diabetes. While insulin therapy reduces ketogenesis this approach is sub-optimal. Here, we report an insulin-independent pathway able to normalize diabetic ketogenesis. By generating insulin deficient male mice lacking or re-expressing Toll-Like Receptor 4 (TLR4) only in liver or hepatocytes, we demonstrate that hepatic TLR4 in non-parenchymal cells mediates the ketogenesis-suppressing action of S100A9. Mechanistically, S100A9 acts extracellularly to activate the mechanistic target of rapamycin complex 1 (mTORC1) in a TLR4-dependent manner. Accordingly, hepatic-restricted but not hepatocyte-restricted loss of Tuberous Sclerosis Complex 1 (TSC1, an mTORC1 inhibitor) corrects insulin-deficiency-induced hyperketonemia. Therapeutically, recombinant S100A9 administration restrains ketogenesis and improves hyperglycemia without causing hypoglycemia in diabetic mice. Also, circulating S100A9 in patients with ketoacidosis is only marginally increased hence unveiling a window of opportunity to pharmacologically augment S100A9 for preventing unrestrained ketogenesis. In summary, our findings reveal the hepatic S100A9-TLR4-mTORC1 axis in non-parenchymal cells as a promising therapeutic target for restraining diabetic ketogenesis.

Excess ketogenesis can lead to ketoacidosis, a serious complication in patients with diabetes. Here the authors report an insulin independent pathway, the hepatic nonparenchymal S100A9-TLR4-mTORC1 axis, that is able to normalize diabetic ketogenesis and pre-clinical data to suggest potential for development of S100A9 based adjunctive therapy to insulin.

The ventromedial hypothalamic nucleus: watchdog of whole-body glucose homeostasis

The brain, particularly the ventromedial hypothalamic nucleus (VMH), has been long known for its involvement in glucose sensing and whole-body glucose homeostasis. However, it is still not fully understood how the brain detects and responds to the changes in the circulating glucose levels, as well as brain-body coordinated control of glucose homeostasis. In this review, we address the growing evidence implicating the brain in glucose homeostasis, especially in the contexts of hypoglycemia and diabetes. In addition to neurons, we emphasize the potential roles played by non-neuronal cells, as well as extracellular matrix in the hypothalamus in whole-body glucose homeostasis. Further, we review the ionic mechanisms by which glucose-sensing neurons sense fluctuations of ambient glucose levels. We also introduce the significant implications of heterogeneous neurons in the VMH upon glucose sensing and whole-body glucose homeostasis, in which sex difference is also addressed. Meanwhile, research gaps have also been identified, which necessities further mechanistic studies in future.

Harnessing the Power of Leptin: The Biochemical Link Connecting Obesity, Diabetes, and Cognitive Decline

In this review, the current understanding of leptin’s role in energy balance, glycemic regulation, and cognitive function is examined, and its involvement in maintaining the homeostatic “harmony” of these physiologies is explored. The effects of exercise on circulating leptin levels are summarized, and the results of clinical application of leptin to metabolic disease and neurologic dysfunction are reviewed. Finally, pre-clinical evidence is presented which suggests that synthetic peptide leptin mimetics may be useful in resolving not only the leptin resistance associated with common obesity and other elements of metabolic syndrome, but also the peripheral insulin resistance characterizing type 2 diabetes mellitus, and the central insulin resistance associated with certain neurologic deficits in humans.

Roles of plasma leptin and resistin in novel subgroups of type 2 diabetes driven by cluster analysis

Background

A novel classification has been introduced to promote precision medicine in diabetes. The current study aimed to investigate the relationship between leptin and resistin levels with novel refined subgroups in patients with type 2 diabetes mellitus (T2DM).

Methods

The k-means analysis was conducted to cluster 541 T2DM patients into the following four subgroups: mild obesity-related diabetes (MOD), severe insulin-deficient diabetes (SIDD), severe insulin-resistant diabetes (SIRD) and mild age-related diabetes (MARD). Individuals meeting the exclusion criteria were eliminated, the data for 285 patients were analyzed. Characteristics were determined using various clinical parameters. Both the leptin and resistin levels were determined using enzyme-linked immunosorbent assay.

Results

The highest levels of plasma leptin were in the MOD group with relatively lower levels in the SIDD and SIRD groups (P < 0.001). The SIRD group had a higher resistin concentration than the MARD group (P = 0.024) while no statistical significance in resistin levels was found between the SIDD and MOD groups. Logistic regression demonstrated that plasma resistin was associated with a higher risk of diabetic nephropathy (odds ratios (OR) = 2.255, P = 0.001). According to receiver operating characteristic (ROC) curves, the area under the curve (AUC) of resistin (0.748, 95% CI 0.610–0.887) was significantly greater than that of HOMA2-IR (0.447, 95% CI 0.280–0.614) (P < 0.05) for diabetic nephropathy in the SIRD group.

Conclusions

Leptin levels were different in four subgroups of T2DM and were highest in the MOD group. Resistin was elevated in the SIRD group and was closely related to diabetic nephropathy.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12944-022-01623-z.

Central Nervous System Control of Glucose Homeostasis: A Therapeutic Target for Type 2 Diabetes?

Historically, pancreatic islet beta cells have been viewed as principal regulators of glycemia, with type 2 diabetes (T2D) resulting when insulin secretion fails to compensate for peripheral tissue insulin resistance. However, glycemia is also regulated by insulin-independent mechanisms that are dysregulated in T2D. Based on evidence supporting its role both in adaptive coupling of insulin secretion to changes in insulin sensitivity and in the regulation of insulin-independent glucose disposal, the central nervous system (CNS) has emerged as a fundamental player in glucose homeostasis. Here, we review and expand upon an integrative model wherein the CNS, together with the islet, establishes and maintains the defended level of glycemia. We discuss the implications of this model for understanding both normal glucose homeostasis and T2D pathogenesis and highlight centrally targeted therapeutic approaches with the potential to restore normoglycemia to patients with T2D.

Peripheral combination treatment of leptin and an SGLT2 inhibitor improved glucose metabolism in insulin-dependent diabetes mellitus mice

We investigated whether peripheral combination treatment of a sodium-glucose cotransporter 2 (SGLT2) inhibitor and leptin improves glucose metabolism in insulin-dependent diabetes mellitus (IDDM) model mice. Twelve-week-old male C57BL6 mice were intraperitoneally administered a high dose of streptozotocin to produce IDDM. IDDM mice were then divided into five groups: SGLT2 inhibitor treatment alone, leptin treatment alone, leptin and SGLT2 inhibitor co-treatment, untreated IDDM mice, and healthy mice groups. The blood glucose (BG) level at the end of the dark cycle was measured, and a glucose tolerance test (GTT) was performed and compared between the five groups. Leptin was peripherally administered at 20 μg/day using an osmotic pump, and an SGLT2 inhibitor, ipragliflozin, was orally administered at 3 mg/kg/day. Monotherapy with SGLT2 inhibitor or leptin significantly improved glucose metabolism in mice as evaluated by BG and GTT compared with the untreated group, whereas the co-treatment group with SGLT2 inhibitor and leptin further improved glucose metabolism as compared with the monotherapy group. Notably, glucose metabolism in the co-treatment group improved to the same level as that in the healthy mice group. Thus, peripheral combination treatment with leptin and SGLT2 inhibitor improved glucose metabolism in IDDM mice without the use of insulin.

Partial Replacement of Dietary Fat with Polyunsaturated Fatty Acids Attenuates the Lipopolysaccharide-Induced Hepatic Inflammation in Sprague-Dawley Rats Fed a High-Fat Diet

In this study, we investigated whether the partial replacement of dietary fat with polyunsaturated fatty acids (PUFAs) ameliorated the lipopolysaccharide (LPS)-induced hepatic inflammation in rats fed a high-fat diet. Male Sprague-Dawley rats were divided into three groups and provided each of the following diets: (1) high-fat diet (HFD), (2) HFD with perilla oil (PO), and (3) HFD with corn oil (CO). After 12 weeks of dietary intervention, the rats were intraperitoneally injected with LPS (5 mg/kg) from Escherichia coli O55:B5 or phosphate-buffered saline (PBS). Following LPS stimulation, serum insulin levels were increased, while PO and CO lowered the serum levels of glucose and insulin. In the liver, LPS increased the triglyceride levels, while PO and CO alleviated the LPS-induced hepatic triglyceride accumulation. In the LPS injected rats, the mRNA expression of genes related to inflammation and endoplasmic reticulum (ER) stress was attenuated by PO and CO in the liver. Furthermore, hepatic levels of proteins involved in the nuclear factor kappa-light-chain-enhancer of activated B cells/mitogen-activated protein kinase pathways, antioxidant response, and ER stress were lowered by PO- and CO-replacement. Therefore, the partial replacement of dietary fat with PUFAs alleviates LPS-induced hepatic inflammation during HFD consumption, which may decrease metabolic abnormalities.

Trajectory of leptin and leptin receptor in vertebrates: Structure, function and their regulation

The present review provides a comparative insight into structure, function and control of leptin system in fishes, herptiles, birds and mammals. In general, leptin acts as an anorexigenic hormone since its administration results in decrease of food intake in vertebrates. Nonetheless, functional paradox arises in fishes from contradictory observations on level of leptin during fasting and re-feeding. In addition, leptin is shown to modulate metabolic functions in fishes, reptiles, birds and mammals. Leptin also regulates reproductive and immune functions though more studies are warranted in non-mammalian vertebrates. The expression of leptin and its receptor is influenced by numerous factors including sex steroids, stress and stress-induced catecholamines and glucocorticoids though their effect in non-mammalian vertebrates is hard to be generalized due to limited studies.

Rap1 in the VMH regulates glucose homeostasis

The hypothalamus is a critical regulator of glucose metabolism and is capable of correcting diabetes conditions independently of an effect on energy balance. The small GTPase Rap1 in the forebrain is implicated in high-fat diet–induced (HFD-induced) obesity and glucose imbalance. Here, we report that increasing Rap1 activity selectively in the medial hypothalamus elevated blood glucose without increasing the body weight of HFD-fed mice. In contrast, decreasing hypothalamic Rap1 activity protected mice from diet-induced hyperglycemia but did not prevent weight gain. The remarkable glycemic effect of Rap1 was reproduced when Rap1 was specifically deleted in steroidogenic factor-1–positive (SF-1–positive) neurons in the ventromedial hypothalamic nucleus (VMH) known to regulate glucose metabolism. While having no effect on body weight regardless of sex, diet, and age, Rap1 deficiency in the VMH SF1 neurons markedly lowered blood glucose and insulin levels, improved glucose and insulin tolerance, and protected mice against HFD-induced neural leptin resistance and peripheral insulin resistance at the cellular and whole-body levels. Last, acute pharmacological inhibition of brain exchange protein directly activated by cAMP 2, a direct activator of Rap1, corrected glucose imbalance in obese mouse models. Our findings uncover the primary role of VMH Rap1 in glycemic control and implicate Rap1 signaling as a potential target for therapeutic intervention in diabetes.

Central nervous system regulation of organismal energy and glucose homeostasis

Growing evidence implicates the brain in the regulation of both immediate fuel availability (for example, circulating glucose) and long-term energy stores (that is, adipose tissue mass). Rather than viewing the adipose tissue and glucose control systems separately, we suggest that the brain systems that control them are components of a larger, highly integrated, 'fuel homeostasis' control system. This conceptual framework, along with new insights into the organization and function of distinct neuronal systems, provides a context within which to understand how metabolic homeostasis is achieved in both basal and postprandial states. We also review evidence that dysfunction of the central fuel homeostasis system contributes to the close association between obesity and type 2 diabetes, with the goal of identifying more effective treatment options for these common metabolic disorders.

A neural basis for brain leptin action on reducing type 1 diabetic hyperglycemia

Central leptin action rescues type 1 diabetic (T1D) hyperglycemia; however, the underlying mechanism and the identity of mediating neurons remain elusive. Here, we show that leptin receptor (LepR)-expressing neurons in arcuate (LepRArc) are selectively activated in T1D. Activation of LepRArc neurons, Arc GABAergic (GABAArc) neurons, or arcuate AgRP neurons, is able to reverse the leptin's rescuing effect. Conversely, inhibition of GABAArc neurons, but not AgRP neurons, produces leptin-mimicking rescuing effects. Further, AgRP neuron function is not required for T1D hyperglycemia or leptin's rescuing effects. Finally, T1D LepRArc neurons show defective nutrient sensing and signs of cellular energy deprivation, which are both restored by leptin, whereas nutrient deprivation reverses the leptin action. Our results identify aberrant activation of LepRArc neurons owing to energy deprivation as the neural basis for T1D hyperglycemia and that leptin action is mediated by inhibiting LepRArc neurons through reversing energy deprivation.

Investigating potential protein markers of cardiovascular disease in children with type 1 diabetes mellitus

BACKGROUND

Type 1 diabetes mellitus (T1DM) is a metabolic disease characterized by dysglycaemia. Cardiovascular disease (CVD) is a major complication among T1DM patients and the leading cause of mortality later in life.

METHODS

The study subjects consisted of T1DM children with poor glycemic control (HbA1c > 7.5%) and healthy age and gender matched controls. Venous blood samples were collected and tested by utilizing a novel immunoassay panel with 96 protein biomarkers. Data were analyzed using non-linear regression analysis and the expression of biomarkers was compared between T1DM and healthy control groups using an unpaired student's t-test. Dynamic principal component analysis (PCA) was operated based on the differentially expressed proteins.

RESULTS

Ten T1DM children and 10 healthy controls were analyzed. Twelve CVD markers show significant differential expression between T1DM patients and healthy controls (p < 0.05). Dynamic PCA clustering based on differentially expressed proteins demonstrated an obvious clustering between the two populations.

CONCLUSIONS

This preliminary study reveals the feasibility of utilizing a novel immunoassay panel to investigate potential biomarkers for predicting incipient CVD in children with T1DM. In future, longitudinal studies are required to track the relationships between measurements of the selected protein markers and the development of CVD in T1DM patients.

Association of insulin resistance and leptin receptor gene polymorphism in type 2 diabetes mellitus

BACKGROUND

Type 2 diabetes mellitus (T2DM) is a chronic disease that is characterized by impaired glucose metabolism and insulin resistance. The objectives of the study were to evaluate the pattern of leptin receptor gene polymorphism Gln223Arg in T2DM and to identify its association with the serum leptin and insulin levels as well as with insulin resistance in diabetes.

METHODS

In this cross-sectional study, genotyping of leptin receptor was done for Gln223Arg alleles by PCR-restriction fragment length polymorphism in 39 patients with type 2 diabetes. Serum leptin and insulin levels were assayed using enzyme linked sorbent assay in 39 cases and 45 nondiabetic controls. Insulin resistance was calculated by the homeostasis model assessment of insulin resistance (HOMA-IR) formula. Statistical analysis was performed with Graph pad Instat version 3.

RESULTS

Hardy-Weinberg Equilibrium for the leptin receptor (LEPR) gene variants showed that alleles were in equilibrium. Leptin levels were insignificantly low in patients with diabetes compared to those in controls. Women in the control group showed significantly higher leptin levels (p < 0.05) compared with men. There was a significant difference in the serum insulin levels and insulin resistance (HOMA-IR) among patients with different genotypes (p = 0.04 and p = 0.0378, respectively).

CONCLUSION

Leptin receptor gene polymorphism affected glucose metabolism by altering insulin resistance and pancreatic beta cells. Thus, single-nucleotide polymorphism of LEPR may affect the pathogenesis of T2DM.

Central regulation of glucose metabolism in an insulin-dependent and -independent manner

The central nervous system (CNS) contributes significantly to glucose homeostasis. The available evidence indicates that insulin directly acts on the CNS, in particular the hypothalamus, to regulate hepatic glucose production, thereby controlling whole-body glucose metabolism. Additionally, insulin also acts on the brain to regulate food intake and fat metabolism, which may indirectly regulate glucose metabolism. Studies conducted over the last decade have found that the CNS can regulate glucose metabolism in an insulin-independent manner. Enhancement of central leptin signalling reverses hyperglycaemia in insulin-deficient rodents. Here, I review the mechanisms by which central insulin and leptin actions regulate glucose metabolism. Although clinical studies have shown that insulin treatment is currently indispensable for managing diabetes, unravelling the neuronal mechanisms underlying the central regulation of glucose metabolism will pave the way for the design of novel therapeutic drugs for diabetes.

Increasing hepatic glycogen moderates the diabetic phenotype in insulin-deficient Akita mice

Hepatic glycogen metabolism is impaired in diabetes. We previously demonstrated that strategies to increase liver glycogen content in a high-fat-diet mouse model of obesity and insulin resistance led to a reduction in food intake and ameliorated obesity and glucose tolerance. These effects were accompanied by a decrease in insulin levels, but whether this decrease contributed to the phenotype observed in this animal was unclear. Here we sought to evaluate this aspect directly, by examining the long-term effects of increasing liver glycogen in an animal model of insulin-deficient and monogenic diabetes, namely the Akita mouse, which is characterized by reduced insulin production. We crossed Akita mice with animals overexpressing protein targeting to glycogen (PTG) in the liver to generate Akita mice with increased liver glycogen content (Akita-PTG^OE). Akita-PTG^OE animals showed lower glycemia, lower food intake, and decreased water consumption and urine output compared with Akita mice. Furthermore, Akita-PTG^OE mice showed a restoration of the hepatic energy state and a normalization of gluconeogenesis and glycolysis back to nondiabetic levels. Moreover, hepatic lipogenesis, which is reduced in Akita mice, was reverted in Akita-PTG^OE animals. These results demonstrate that strategies to increase liver glycogen content lead to the long-term reduction of the diabetic phenotype, independently of circulating insulin.

Tissue-Specific Effects of Leptin on Glucose and Lipid Metabolism

The discovery of leptin was intrinsically associated with its ability to regulate body weight. However, the effects of leptin are more far-reaching and include profound glucose-lowering and anti-lipogenic effects, independent of leptin's regulation of body weight. Regulation of glucose metabolism by leptin is mediated both centrally and via peripheral tissues and is influenced by the activation status of insulin signaling pathways. Ectopic fat accumulation is diminished by both central and peripheral leptin, an effect that is beneficial in obesity-associated disorders. The magnitude of leptin action depends upon the tissue, sex, and context being examined. Peripheral tissues that are of particular relevance include the endocrine pancreas, liver, skeletal muscle, adipose tissues, immune cells, and the cardiovascular system. As a result of its potent metabolic activity, leptin is used to control hyperglycemia in patients with lipodystrophy and is being explored as an adjunct to insulin in patients with type 1 diabetes. To fully understand the role of leptin in physiology and to maximize its therapeutic potential, the mechanisms of leptin action in these tissues needs to be further explored.

Metabolic diseases affect male reproduction and induce signatures in gametes that may compromise the offspring health

The most prevalent diseases worldwide are non-communicable such as obesity and type 2 diabetes. Noteworthy, the prevalence of obesity and type 2 diabetes is expected to steadily increase in the next decades, mostly fueled by bad feeding habits, stress, and sedentarism. The reproductive function of individuals is severely affected by abnormal metabolic environments, both at mechanical and biochemical levels. Along with mechanical dysfunctions, and decreased sperm quality (promoted both directly and indirectly by metabolic abnormalities), several studies have already reported the potentially harmful effects of metabolic disorders in the genetic and epigenetic cargo of spermatozoa, and the epigenetic inheritance of molecular signatures induced by metabolic profile (paternal diet, obesity, and diabetes). The inheritance of epigenetic factors towards the development of metabolic abnormalities means that more people in reproductive age can potentially suffer from these disorders and for longer periods. In its turn, these individuals can also transmit this (epi)genetic information to future generations, creating a vicious cycle. In this review, we collect the reported harmful effects related to acquired metabolic disorders and diet in sperm parameters and male reproductive potential. Besides, we will discuss the novel findings regarding paternal epigenetic inheritance, particularly the ones induced by paternal diet rich in fats, obesity, and type 2 diabetes. We analyze the data attained with in vitro and animal models as well as in long-term transgenerational population studies. Although the findings on this topic are very recent, epigenetic inheritance of metabolic disease has a huge societal impact, which may be crucial to tackle the 'fat epidemic' efficiently.

Leptin Receptors in RIP-Cre25Mgn Neurons Mediate Anti-dyslipidemia Effects of Leptin in Insulin-Deficient Mice

Leptin is a potent endocrine hormone produced by adipose tissue and regulates a broad range of whole-body metabolism such as glucose and lipid metabolism, even without insulin. Central leptin signaling can lower hyperglycemia in insulin-deficient rodents via multiple mechanisms, including improvements of dyslipidemia. However, the specific neurons that regulate anti-dyslipidemia effects of leptin remain unidentified. Here we report that leptin receptors (LEPRs) in neurons expressing Cre recombinase driven by a short fragment of a promoter region of Ins2 gene (RIP-Cre25Mgn neurons) are required for central leptin signaling to reverse dyslipidemia, thereby hyperglycemia in insulin-deficient mice. Ablation of LEPRs in RIP-Cre25Mgn neurons completely blocks glucose-lowering effects of leptin in insulin-deficient mice. Further investigations reveal that insulin-deficient mice lacking LEPRs in RIP-Cre25Mgn neurons (RIP-CreΔLEPR mice) exhibit greater lipid levels in blood and liver compared to wild-type controls, and that leptin injection into the brain does not suppress dyslipidemia in insulin-deficient RIP-CreΔLEPR mice. Leptin administration into the brain combined with acipimox, which lowers blood lipids by suppressing triglyceride lipase activity, can restore normal glycemia in insulin-deficient RIP-CreΔLEPR mice, suggesting that excess circulating lipids are a driving-force of hyperglycemia in these mice. Collectively, our data demonstrate that LEPRs in RIP-Cre25Mgn neurons significantly contribute to glucose-lowering effects of leptin in an insulin-independent manner by improving dyslipidemia.

Short-Chain Fatty Acids and Their Association with Signalling Pathways in Inflammation, Glucose and Lipid Metabolism

Short-chain fatty acids (SCFAs), particularly acetate, propionate and butyrate, are mainly produced by anaerobic fermentation of gut microbes. SCFAs play an important role in regulating energy metabolism and energy supply, as well as maintaining the homeostasis of the intestinal environment. In recent years, many studies have shown that SCFAs demonstrate physiologically beneficial effects, and the signalling pathways related to SCFA production, absorption, metabolism, and intestinal effects have been discovered. Two major signalling pathways concerning SCFAs, G-protein-coupled receptors (GPRCs) and histone deacetylases (HDACs), are well recognized. In this review, we summarize the recent advances concerning the biological properties of SCFAs and the signalling pathways in inflammation and glucose and lipid metabolism.

Diabetes mellitus and the impairment of male reproductive function: Possible signaling pathways

BACKGROUND AND AIMS

Today, it has been shown that diabetes mellitus (DM) can affect male fertility. Glucose metabolism is a vital process in spermatogenesis that is impacted by diabetes condition. But the mechanisms by which DM causes male infertility are not wholly clarified. The aim of this review is to provide brief information about the influence of hyperglycemia on male fertility and specific emphasis on the molecular signaling pathway that is involved.

METHODS

Broad literature search in the electronic database "Pubmed", "Google Scholar", the website of "World Health Organization" (WHO) and Control Disease and Prevention (CDC) took place. There was no time restriction. A key criterion for the selection of articles was English and language. Finally, one hundred thirty seven articles were included in the review.

RESULTS

Diabetes mellitus affects many signaling pathways that involved in the spermatogenesis. It seems that increased ROS and oxidative stress in the diabetes is the beginning of all fertility problems and affects all of involved signaling pathways in the spermatogenesis.

CONCLUSIONS

It seems that there was strong interconnected between oxidative stress and all of involved signaling pathways in the reproductive problems in diabetes. So, approaches that diminish oxidative stress in the testis can be effective in improving diabetes related infertility complications.

There and Back Again: Leptin Actions in White Adipose Tissue

Leptin is a hormone discovered almost 30 years ago with important implications in metabolism. It is primarily produced by white adipose tissue (WAT) in proportion to the amount of fat. The discovery of leptin was a turning point for two principle reasons: on one hand, it generated promising expectations for the treatment of the obesity, and on the other, it changed the classical concept that white adipose tissue was simply an inert storage organ. Thus, adipocytes in WAT produce the majority of leptin and, although its primary role is the regulation of fat stores by controlling lipolysis and lipogenesis, this hormone also has implications in other physiological processes within WAT, such as apoptosis, browning and inflammation. Although a massive number of questions related to leptin actions have been answered, the necessity for further clarification facilitates constantly renewing interest in this hormone and its pathways. In this review, leptin actions in white adipose tissue will be summarized in the context of obesity.

A leptin-BDNF pathway regulating sympathetic innervation of adipose tissue

Mutations in the leptin gene (ob) result in a metabolic disorder that includes severe obesity¹, and defects in thermogenesis² and lipolysis³, both of which are adipose tissue functions regulated by the sympathetic nervous system. However, the basis of these sympathetic-associated abnormalities remains unclear. Furthermore, chronic leptin administration reverses these abnormalities in adipose tissue, but the underlying mechanism remains to be discovered. Here we report that ob/ob mice, as well as leptin-resistant diet-induced obese mice, show significant reductions of sympathetic innervation of subcutaneous white and brown adipose tissue. Chronic leptin treatment of ob/ob mice restores adipose tissue sympathetic innervation, which in turn is necessary to correct the associated functional defects. The effects of leptin on innervation are mediated via agouti-related peptide and pro-opiomelanocortin neurons in the hypothalamic arcuate nucleus. Deletion of the gene encoding the leptin receptor in either population leads to reduced innervation in fat. These agouti-related peptide and pro-opiomelanocortin neurons act via brain-derived neurotropic factor-expressing neurons in the paraventricular nucleus of the hypothalamus (BDNF^PVH). Deletion of BDNF^PVH blunts the effects of leptin on innervation. These data show that leptin signalling regulates the plasticity of sympathetic architecture of adipose tissue via a top-down neural pathway that is crucial for energy homeostasis.

Targeting perivascular and epicardial adipose tissue inflammation: therapeutic opportunities for cardiovascular disease

Major shifts in human lifestyle and dietary habits toward sedentary behavior and refined food intake triggered steep increase in the incidence of metabolic disorders including obesity and Type 2 diabetes. Patients with metabolic disease are at a high risk of cardiovascular complications ranging from microvascular dysfunction to cardiometabolic syndromes including heart failure. Despite significant advances in the standards of care for obese and diabetic patients, current therapeutic approaches are not always successful in averting the accompanying cardiovascular deterioration. There is a strong relationship between adipose inflammation seen in metabolic disorders and detrimental changes in cardiovascular structure and function. The particular importance of epicardial and perivascular adipose pools emerged as main modulators of the physiology or pathology of heart and blood vessels. Here, we review the peculiarities of these two fat depots in terms of their origin, function, and pathological changes during metabolic deterioration. We highlight the rationale for pharmacological targeting of the perivascular and epicardial adipose tissue or associated signaling pathways as potential disease modifying approaches in cardiometabolic syndromes.

Adipokines as key players in β cell function and failure

The growing prevalence of obesity and its related metabolic diseases, mainly Type 2 diabetes (T2D), has increased the interest in adipose tissue (AT) and its role as a principal metabolic orchestrator. Two decades of research have now shown that ATs act as an endocrine organ, secreting soluble factors termed adipocytokines or adipokines. These adipokines play crucial roles in whole-body metabolism with different mechanisms of action largely dependent on the tissue or cell type they are acting on. The pancreatic β cell, a key regulator of glucose metabolism due to its ability to produce and secrete insulin, has been identified as a target for several adipokines. This review will focus on how adipokines affect pancreatic β cell function and their impact on pancreatic β cell survival in disease contexts such as diabetes. Initially, the "classic" adipokines will be discussed, followed by novel secreted adipocyte-specific factors that show therapeutic promise in regulating the adipose-pancreatic β cell axis.

Interaction of glucose sensing and leptin action in the brain

Background

In response to energy abundant or deprived conditions, nutrients and hormones activate hypothalamic pathways to maintain energy and glucose homeostasis. The underlying CNS mechanisms, however, remain elusive in rodents and humans.

Scope of review

Here, we first discuss brain glucose sensing mechanisms in the presence of a rise or fall of plasma glucose levels, and highlight defects in hypothalamic glucose sensing disrupt in vivo glucose homeostasis in high-fat fed, obese, and/or diabetic conditions. Second, we discuss brain leptin signalling pathways that impact glucose homeostasis in glucose-deprived and excessed conditions, and propose that leptin enhances hypothalamic glucose sensing and restores glucose homeostasis in short-term high-fat fed and/or uncontrolled diabetic conditions.

Major conclusions

In conclusion, we believe basic studies that investigate the interaction of glucose sensing and leptin action in the brain will address the translational impact of hypothalamic glucose sensing in diabetes and obesity.

New Frontiers for the Use of IP6 and Inositol Combination in Treating Diabetes Mellitus: A Review

Inositol, or myo-inositol, and associated analog molecules, including myo-inositol hexakisphosphate, are known to possess beneficial biomedical properties and are now being widely studied. The impact of these compounds in improving diabetic indices is significant, especially in light of the high cost of treating diabetes mellitus and associated disorders globally. It is theorized that, within ten years, the global population of people with the disease will reach 578 million individuals, with the cost of care projected to be approximately 2.5 trillion dollars. Natural alternatives to pharmaceuticals are being sought, and this has led to studies involving inositol, and myo-inositol-hexakisphosphate, also referred to as IP6. It has been reported that IP6 can improve diabetic indices and regulate the activities of some metabolic enzymes involved in lipid and carbohydrate metabolism. Current research activities have been focusing on the mechanisms of action of inositol and IP6 in the amelioration of the indices of diabetes mellitus. We demonstrated that an IP6 and inositol combination supplement may regulate insulin secretion, modulate serum leptin concentrations, food intake, and associated weight gain, which may be beneficial in both prediabetic and diabetic states. The supplement attenuates vascular damage by reducing red cell distribution width. Serum HDL is increased while serum triglycerides tend to decrease with consumption of the combination supplement, perhaps due to the modulation of lipogenesis involving reduced serum lipase activity. We also noted increased fecal lipid output following combination supplement consumption. Importantly, liver function was found to be preserved. Concurrently, serum reactive oxygen species production was reduced, indicating that inositol and IP6 supplement consumption may reduce free radical damage to tissues and organs as well as serum lipids and blood glucose by preserving liver function. This review provides an overview of the findings associated with inositol and IP6 supplementation in the effective treatment of diabetes with a view to proposing the potential mechanisms of action.

A case of generalized lipodystrophy-associated progeroid syndrome treated by leptin replacement with short and long-term monitoring of the metabolic and endocrine profiles

We herein report a case of a 28-year-old man with generalized lipodystrophy-associated progeroid syndrome treated by leptin replacement. He showed symptoms of generalized lipodystrophy around onset of puberty. His body mass index was 11.9 kg/m², and he had a short stature, birdlike facies, dental crowding due to micrognathia, partial graying and loss of hair, and a high-pitched voice, all of which are typical features of the progeroid syndrome. Laboratory examinations and abdominal ultrasonography revealed diabetes mellitus, insulin-resistance, dyslipidemia, decreased serum leptin levels (2.2 ng/mL), elevated serum hepatobiliary enzyme levels and fatty liver. Whole exome sequencing revealed de novo heterozygous LMNA p.T10I mutation, indicating generalized lipodystrophy-associated progeroid syndrome, which is a newly identified subtype of atypical progeroid syndrome characterized by severe metabolic abnormalities. Daily injection of metreleptin [1.2 mg (0.04 mg/kg)/day] was started. Metreleptin treatment significantly improved his diabetes from HbA1c 11.0% to 5.4% in six months. It also elevated serum testosterone levels. Elevated serum testosterone levels persisted even 1 year after the initiation of metreleptin treatment. To the best of our knowledge, this is the first Japanese case report of generalized lipodystrophy-associated progeroid syndrome. Furthermore, we evaluated short and long-term effectiveness of leptin replacement on generalized lipodystrophy by monitoring metabolic and endocrine profiles.

The effect of human wharton's jelly-derived mesenchymal stem cells on MC4R, NPY, and LEPR gene expression levels in rats with streptozotocin-induced diabetes

OBJECTIVES

Type 1 diabetes (T1D) is an autoimmune disease resulting from inflammatory destruction of islets β-cells. Nowadays, progress in cell therapy, especially mesenchymal stem cells (MSCs) proposes numerous potential remedies for T1D. We aimed to investigate the combination therapeutic effect of these cells with insulin and metformin on neuropeptide Y, melanocortin-4 receptor, and leptin receptor genes expression in TID.

MATERIALS AND METHODS

One hundreds male rats were randomly divided into seven groups: the control, diabetes, insulin (Ins.), insulin+metformin (Ins.Met.), Wharton's Jelly-derived MSCs (WJ-MSCs), insulin+metformin+WJ-MSCs (Ins.Met.MSCs), and insulin+WJ-MSCs (Ins.MSCs). Treatment was performed from the first day after diagnosis as diabetes. Groups of the recipient WJ-MSCs were intraportally injected with 2× 10⁶ MSCs/kg at the 7th and 28th days of study. Fasting blood sugar was monitored and tissues and genes analysis were performed.

RESULTS

The blood glucose levels were slightly decreased in all treatment groups within 20th and 45th days compared to the diabetic group. The C-peptide level enhanced in these groups compared to the diabetic group, but this increment in Ins.MSCs group on the 45th days was higher than other groups. The expression level of melanocortin-4 receptor and leptin receptor genes meaningfully up-regulated in the treatment groups, while the expression of neuropeptide Y significantly down-regulated in the treatment group on both times of study.

CONCLUSION

Our data exhibit that infusion of MSCs and its combination therapy with insulin might ameliorate diabetes signs by changing the amount of leptin and subsequent changes in the expression of neuropeptide Y and melanocortin-4 receptor.

Role of POMC and AgRP neuronal activities on glycaemia in mice

Leptin regulates both feeding and glycaemia primarily through its receptors expressed on agouti-related peptide (AgRP) and pro-opiomelanocortin-expressing (POMC) neurons; however, it is unknown whether activity of these neuronal populations mediates the regulation of these processes. To determine this, we injected Cre-dependent designer receptors exclusively activated by designer drugs (DREADD) viruses into the hypothalamus of normoglycaemic and diabetic AgRP-ires-cre and POMC-cre mice to chemogenetically activate or inhibit these neuronal populations. Despite robust changes in food intake, activation or inhibition of AgRP neurons did not affect glycaemia, while activation caused significant (P = 0.014) impairment in insulin sensitivity. Stimulation of AgRP neurons in diabetic mice reversed leptin’s ability to inhibit feeding but did not counter leptin’s ability to lower blood glucose levels. Notably, the inhibition of POMC neurons stimulated feeding while decreasing glucose levels in normoglycaemic mice. The findings suggest that leptin’s effects on feeding by AgRP neurons are mediated by changes in neuronal firing, while the control of glucose balance by these cells is independent of chemogenetic activation or inhibition. The firing-dependent glucose lowering mechanism within POMC neurons is a potential target for the development of novel anti-diabetic medicines.

Impact of leptin deficiency compared with neuronal-specific leptin receptor deletion on cardiometabolic regulation

The main goal of this study was to compare the impact of total body leptin deficiency with neuronal-specific leptin receptor (LR) deletion on metabolic and cardiovascular regulation. Liver fat, diacylglycerol acyltransferase-2 (DGTA2), and CD36 protein content were measured in wild-type (WT), nervous system LR-deficient (LR/Nestin-Cre), and leptin deficient (ob/ob) mice. Blood pressure (BP) and heart rate (HR) were recorded by telemetry, and motor activity (MA) and oxygen consumption (V̇o₂) were monitored at 24 wk of age. Female and male LR/Nestin-Cre and ob/ob mice were heavier than WT mice (62 ± 5 and 61 ± 3 vs. 31 ± 1 g) and hyperphagic (6.2 ± 0.5 and 6.1 ± 0.7 vs. 3.5 ± 1.0 g/day), with reduced V̇o₂ (27 ± 1 and 33 ± 1 vs 49 ± 3 ml·kg^-1·min^-1) and decreased MA (3 ± 1 and 7 ± 2 vs 676 ± 105 cm/h). They were also hyperinsulinemic and hyperglycemic compared with WT mice. LR/Nestin-Cre mice had high levels of plasma leptin, while ob/ob mice had undetectable leptin levels. Despite comparable obesity, LR/Nestin-Cre mice had lower liver fat content, DGTA2, and CD36 protein levels than ob/ob mice. Male WT, LR/Nestin-Cre, and ob/ob mice exhibited similar BP (111 ± 3, 110 ± 1 and 109 ± 2 mmHg). Female LR/Nestin-Cre and ob/ob mice, however, had higher BP than WT females despite similar metabolic phenotypes compared with male LR/Nestin-Cre and ob/ob mice. These results indicate that although nervous system LRs play a crucial role in regulating body weight and glucose homeostasis, peripheral LRs regulate liver fat deposition. In addition, our results suggest potential sex differences in the impact of obesity on BP regulation.

S100A9 extends lifespan in insulin deficiency

Tens of millions suffer from insulin deficiency (ID); a defect leading to severe metabolic imbalance and death. The only means for management of ID is insulin therapy; yet, this approach is sub-optimal and causes life-threatening hypoglycemia. Hence, ID represents a great medical and societal challenge. Here we report that S100A9, also known as Calgranulin B or Myeloid-Related Protein 14 (MRP14), is a leptin-induced circulating cue exerting beneficial anti-diabetic action. In murine models of ID, enhanced expression of S100A9 alone (i.e. without administered insulin and/or leptin) slightly improves hyperglycemia, and normalizes key metabolic defects (e.g. hyperketonemia, hypertriglyceridemia, and increased hepatic fatty acid oxidation; FAO), and extends lifespan by at least a factor of two. Mechanistically, we report that Toll-Like Receptor 4 (TLR4) is required, at least in part, for the metabolic-improving and pro-survival effects of S100A9. Thus, our data identify the S100A9/TLR4 axis as a putative target for ID care.

Insulin replacement is a valuable therapy for insulin deficiency, however, other therapies are being investigated to restore metabolic homeostasis. Here, the authors identify S100A9 as a leptin induced circulating cue that improves glucose and lipid homeostasis and extends survival in insulin deficient mice.

Leptin's hunger-suppressing effects are mediated by the hypothalamic-pituitary-adrenocortical axis in rodents

Leptin informs the brain about sufficiency of fuel stores. When insufficient, leptin levels fall, triggering compensatory increases in appetite. Falling leptin is first sensed by hypothalamic neurons, which then initiate adaptive responses. With regard to hunger, it is thought that leptin-sensing neurons work entirely via circuits within the central nervous system (CNS). Very unexpectedly, however, we now show this is not the case. Instead, stimulation of hunger requires an intervening endocrine step, namely activation of the hypothalamic-pituitary-adrenocortical (HPA) axis. Increased corticosterone then activates AgRP neurons to fully increase hunger. Importantly, this is true for 2 forms of low leptin-induced hunger, fasting and poorly controlled type 1 diabetes. Hypoglycemia, which also stimulates hunger by activating CNS neurons, albeit independently of leptin, similarly recruits and requires this pathway by which HPA axis activity stimulates AgRP neurons. Thus, HPA axis regulation of AgRP neurons is a previously underappreciated step in homeostatic regulation of hunger.