New Insights into the Regulation of Leptin Gene Expression

New concepts in the roles of AMPK in adipocyte stem cell biology

Obesity is a major risk factor for many life-threatening diseases. Adipose tissue dysfunction is emerging as a driving factor in the transition from excess adiposity to comorbidities such as metabolic-associated fatty liver disease, cardiovascular disease, Type 2 diabetes and cancer. However, the transition from healthy adipose expansion to the development of these conditions is poorly understood. Adipose stem cells, residing in the vasculature and stromal regions of subcutaneous and visceral depots, are responsible for the expansion and maintenance of organ function, and are now recognised as key mediators of pathological transformation. Impaired tissue expansion drives inflammation, dysregulation of endocrine function and the deposition of lipids in the liver, muscle and around vital organs, where it is toxic. Contrary to previous hypotheses, it is the promotion of healthy adipose tissue expansion and function, not inhibition of adipogenesis, that presents the most attractive therapeutic strategy in the treatment of metabolic disease. AMP-activated protein kinase, a master regulator of energy homeostasis, has been regarded as one such target, due to its central role in adipose tissue lipid metabolism, and its apparent inhibition of adipogenesis. However, recent studies utilising AMP-activated protein kinase (AMPK)-specific compounds highlight a more subtle, time-dependent role for AMPK in the process of adipogenesis, and in a previously unexplored repression of leptin, independent of adipocyte maturity. In this article, I discuss historic evidence for AMPK-mediated adipogenesis inhibition and the multi-faceted roles for AMPK in adipose tissue.

Leptin is a potential biomarker of childhood obesity and an indicator of the effectiveness of weight-loss interventions

Childhood obesity represents a significant public health concern, imposing a substantial burden on the healthcare system. Furthermore, weight-loss programs often exhibit reduced effectiveness in adults who have a history of childhood obesity. Therefore, early intervention against childhood obesity is imperative. Presently, the primary method for diagnosing childhood obesity relies on body mass index (BMI), yet this approach has inherent limitations. Leptin, a satiety hormone produced by adipocytes, holds promise as a superior tool for predicting both childhood and subsequent adulthood obesity. In this review, we elucidate the tools employed for assessing obesity in children, delve into the biological functions of leptin, and examine the factors governing its expression. Additionally, we discuss maternal and infantile leptin levels as predictors of childhood obesity. By exploring the relationship between leptin levels and weight loss, we present leptin as a potential indicator of the effectiveness of obesity interventions.

Impact of obesity‑associated myeloid‑derived suppressor cells on cancer risk and progression (Review)

Obesity is a chronic disease caused by the accumulation of excessive adipose tissue. This disorder is characterized by chronic low‑grade inflammation, which promotes the release of proinflammatory mediators, including cytokines, chemokines and leptin. Simultaneously, chronic inflammation can predispose to cancer development, progression and metastasis. Proinflammatory molecules are involved in the recruitment of specific cell populations in the tumor microenvironment. These cell populations include myeloid‑derived suppressor cells (MDSCs), a heterogeneous, immature myeloid population with immunosuppressive abilities. Obesity‑associated MDSCs have been linked with tumor dissemination, progression and poor clinical outcomes. A comprehensive literature review was conducted to assess the impact of obesity‑associated MDSCs on cancer in both preclinical models and oncological patients with obesity. A secondary objective was to examine the key role that leptin, the most important proinflammatory mediator released by adipocytes, plays in MDSC‑driven immunosuppression Finally, an overview is provided of the different therapeutic approaches available to target MDSCs in the context of obesity‑related cancer.

Molecular Characterization and Expression Pattern of leptin in Yellow Cheek Carp (Elopichthys bambusa) and Its Transcriptional Changes in Response to Fasting and Refeeding

Leptin, a secretory protein encoded by obese genes, plays an important role in regulating feeding and energy metabolism in fish. To study the structure and function of the Leptin gene in yellow cheek carp (Elopichthys bambusa), the full-length cDNA sequence of leptin was cloned, named EbLep. The full-length cDNA of Eblep was 1140 bp, and the length of the open reading frame (ORF), which can encode a protein of 174 amino acids, was 525 bp. The signal peptide was predicted to contain 33 amino acids. Sequence alignment showed that the amino acid sequence of Leptin was conserved in cyprinid fish. Despite large differences between primary structures, the tertiary structure of the EbLep protein was similar to that of the human protein and had four α-helices. The EbLep mRNA transcript was detected in all tested tissues, with the highest expression in the liver and lowest expression in the spleen. In this study, short-term fasting significantly increased the mRNA expression of EbLep in the liver, which returned to a normal level after 6 days of refeeding and was significantly lower than the normal level after 28 days of refeeding. In the brain, the mRNA expression of EbLep significantly decreased during short-term fasting and significantly increased to a higher value than the control group after 1 h of refeeding. It then rapidly decreased to a lower value than the control group after 6 h of refeeding, returning to the normal level after 1 day of refeeding, and significantly decreasing to a lower value than the control group after 28 days of refeeding. To sum up, the change in the mRNA expression of EbLep in the brain and liver may be an adaptive strategy for different energy levels.

Circulating leptin and its correlation with rheumatoid arthritis activity: a meta-analysis

Objective

The aim of the study was to investigate the association between the levels of leptin in the circulating of individuals with rheumatoid arthritis (RA) and the severity of the disease.

Methods

We looked through the databases of Embase, Medline, and the Cochrane Library. We conducted a meta-analysis on the correlations between circulating leptin and the Disease Activity Score 28-erythrocyte sedimentation rate (DAS28-ESR) and C-reactive protein (CRP) levels in RA patients, as well as a meta-analysis of circulating or circulating leptin levels in RA patients.

Results

This meta-analysis study analyzed 42 different comparisons from 37 different publications, including a total of 2,350 patients with RA and 1,815 controls. The RA group had substantially higher leptin levels than the control group (standardized mean difference [SMD]=0.507, 95% confidence interval [CI]=0.309~0.704, p<0.001). The finding that RA patients had higher leptin levels was unaffected by sample size. The correlation between circulating leptin levels and DAS28 is statistically significant (correlation coefficient=0.247, 95% CI=0.087~0.396, p=0.003). Leptin levels are also correlated with CRP levels (correlation coefficient=0.203, 95% CI=0.048~0.349, p=0.010).

Conclusion

This comprehensive meta-analysis demonstrates that the circulating leptin levels of RA patients are elevated, and provides compelling evidence of the significant relationship between leptin levels and the activity of RA. The findings of this research suggest that leptin plays a significant role in the pathophysiology of this disease.

LncOb rs10487505 variant is associated with leptin levels in pediatric non-alcoholic fatty liver disease

BACKGROUND

Low and high leptin levels are associated with non-alcoholic fatty liver disease (NAFLD). The LncOb rs10487505 variant has been associated with body mass index (BMI), and the C allele was reported as leptin-lowering. We evaluated the association of rs10487505 with leptin levels, liver histology, and surgery-induced weight loss in youths with NAFLD.

METHODS

One-hundred five obese youths with NAFLD, of whom 19 undergoing laparoscopic sleeve gastrectomy (LSG), were analyzed for rs10487505 and leptin circulating levels.

RESULTS

The G allele frequency was lower in youths with NAFLD than in controls (p = 0.049). No difference was found in anthropometrics, biochemistry and histology between G allele carriers and CC homozygotes, except for leptin levels (p = 0.016). Leptin correlated with body weight, BMI, BMI-z score, waist circumference, insulin resistance/sensitivity, and triglycerides (p ≤ 0.01). A multivariable regression model including body weight and homeostasis model assessment of insulin resistance was a good predictor of plasma leptin (R² = 0.45), and the addition of genotype to the model increased the R² to 0.50. Following LSG, leptin levels and body weight were more reduced in G allele carriers (p < 0.05).

CONCLUSIONS

LncOb rs10487505 variant was associated with pediatric NAFLD and high leptin levels, and with weight and leptin reduction after LSG in youths.

IMPACT

The interplay of environment, genetics and epigenetics is crucial inflating the risk of non-alcoholic fatty liver disease (NAFLD). Several long non-coding RNA (LncRNAs) are found associated with NAFLD pathogenesis. Here, we evaluated the impact of the genetic variant rs10487505 in LncOb which is involved in the regulation of leptin gene expression. The LncOb rs10487505 is associated with increased levels of leptin, but not with liver histology, in youths with NAFLD. The LncOb rs10487505 was also associated with the significant decrease of leptin and body weight after bariatric surgery.

Loss of vascular endothelial glutaminase inhibits tumor growth and metastasis, and increases sensitivity to chemotherapy

Glutamine is the most abundant non-essential amino acid in blood stream; yet it's concentration in tumor interstitium is markedly lower than that in the serum, reflecting the huge demand of various cell types in tumor microenvironment for glutamine. While many studies have investigated glutamine metabolism in tumor epithelium and infiltrating immune cells, the role of glutamine metabolism in tumor blood vessels remains unknown. Here, we report that inducible genetic deletion of glutaminase (GLS) specifically in host endothelium, GLSECKO, impairs tumor growth and metastatic dissemination in vivo. Loss of GLS decreased tumor microvascular density, increased perivascular support cell coverage, improved perfusion, and reduced hypoxia in mammary tumors. Importantly, chemotherapeutic drug delivery and therapeutic efficacy were improved in tumor-bearing GLSECKO hosts or in combination with GLS inhibitor, CB839. Mechanistically, loss of GLS in tumor endothelium resulted in decreased leptin levels, and exogenous recombinant leptin rescued tumor growth defects in GLSECKO mice. Together, these data demonstrate that inhibition of endothelial glutamine metabolism normalizes tumor vessels, reducing tumor growth and metastatic spread, improving perfusion, and reducing hypoxia, and enhancing chemotherapeutic delivery. Thus, targeting glutamine metabolism in host vasculature may improve clinical outcome in patients with solid tumors.

Leptin Methylation and mRNA Expression Associated With Psychopathology in Schizophrenia Inpatients

Leptin involved in the regulation of dopaminergic neurons of the central nervous system may confirm the hypothesis of neurodevelopment in schizophrenic patients. However, specific genetic mechanisms are undefined. Therefore, we aimed to explore the regulation of DNA methylation of leptin promoters and mRNA expression in patients with schizophrenia. A cross-sectional study enrolled 40 patients and 40 healthy controls from the Beijing Huilongguan Hospital in China. The leptin methylation levels and mRNA expression were examined by highly sensitive mass spectrometry based on the MassARRAY System and real-time quantitative polymerase chain reaction (qPCR). The Positive and Negative Symptoms Scale (PANSS) was applied to estimate the clinical symptoms of patients. The LEP-CpG7 and CpG15 methylation in patients were significantly higher than in healthy controls (P < 0.05). The LEP-CpG11, CpG33.34.35, CpG36 methylation, and mRNA expression decreased significantly in patients compared with healthy controls (P < 0.05). After controlling gender, age, BMI, dose of antipsychotic and duration of illness, LEP-CpG7 methylation was negatively associated with PANSS positive symptoms subscore (r = -0.485, P = 0.005). In addition, LEP-mRNA expression was negatively correlated with PANSS total score (r = -0.385, P = 0.03) and positive subscale (r = -0.392, P = 0.026). Nevertheless, only the LEP-CpG7 methylation level remained negatively correlated to the PANSS positive subscore following multiple stepwise regression (β = -17.071, P = 0.037). These results suggest that leptin methylation and mRNA expression might contribute to the pathogenesis of schizophrenia. LEP-CpG7 methylation may be negatively associated with positive symptoms in patients with schizophrenia.

Suggestive Evidence for Causal Effect of Leptin Levels on Risk for Anorexia Nervosa: Results of a Mendelian Randomization Study

Genetic correlations suggest a coexisting genetic predisposition to both low leptin levels and risk for anorexia nervosa (AN). To investigate the causality and direction of these associations, we performed bidirectional two-sample Mendelian randomization (MR) analyses using data of the most recent genome-wide association study (GWAS) for AN and both a GWAS and an exome-wide-association-study (EWAS) for leptin levels. Most MR methods with genetic instruments from GWAS showed a causal effect of lower leptin levels on higher risk of AN (e.g. IVW b = -0.923, p = 1.5 × 10^-4). Because most patients with AN are female, we additionally performed analyses using leptin GWAS data of females only. Again, there was a significant effect of leptin levels on the risk of AN (e.g. IVW b = -0.826, p = 1.1 × 10^-04). MR with genetic instruments from EWAS showed no overall effect of leptin levels on the risk for AN. For the opposite direction, MR revealed no causal effect of AN on leptin levels. If our results are confirmed in extended GWAS data sets, a low endogenous leptin synthesis represents a risk factor for developing AN.

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.

Endocrine role of bone in the regulation of energy metabolism

Bone mainly functions as a supportive framework for the whole body and is the major regulator of calcium homeostasis and hematopoietic function. Recently, an increasing number of studies have characterized the significance of bone as an endocrine organ, suggesting that bone-derived factors regulate local bone metabolism and metabolic functions. In addition, these factors can regulate global energy homeostasis by altering insulin sensitivity, feeding behavior, and adipocyte commitment. These findings may provide a new pathological mechanism for related metabolic diseases or be used in the diagnosis, treatment, and prevention of metabolic diseases such as osteoporosis, obesity, and diabetes mellitus. In this review, we summarize the regulatory effect of bone and bone-derived factors on energy metabolism and discuss directions for future research.

Spinal Cord Injury Reduces Serum Levels of Fibroblast Growth Factor-21 and Impairs Its Signaling Pathways in Liver and Adipose Tissue in Mice

Spinal cord injury (SCI) results in dysregulation of carbohydrate and lipid metabolism; the underlying cellular and physiological mechanisms remain unclear. Fibroblast growth factor 21 (FGF21) is a circulating protein primarily secreted by the liver that lowers blood glucose levels, corrects abnormal lipid profiles, and mitigates non-alcoholic fatty liver disease. FGF21 acts via activating FGF receptor 1 and ß-klotho in adipose tissue and stimulating release of adiponectin from adipose tissue which in turn signals in the liver and skeletal muscle. We examined FGF21/adiponectin signaling after spinal cord transection in mice fed a high fat diet (HFD) or a standard mouse chow. Tissues were collected at 84 days after spinal cord transection or a sham SCI surgery. SCI reduced serum FGF21 levels and hepatic FGF21 expression, as well as β-klotho and FGF receptor-1 (FGFR1) mRNA expression in adipose tissue. SCI also reduced serum levels and adipose tissue mRNA expression of adiponectin and leptin, two major adipokines. In addition, SCI suppressed hepatic type 2 adiponectin receptor (AdipoR2) mRNA expression and PPARα activation in the liver. Post-SCI mice fed a HFD had further suppression of serum FGF21 levels and hepatic FGF21 expression. Elevated serum free fatty acid (FFA) levels after HFD feeding were observed in post-SCI mice but not in sham-mice, suggesting defective FFA uptake after SCI. Moreover, after SCI several genes that are implicated in insulin's action had reduced expression in tissues of interest. These findings suggest that downregulated FGF21/adiponectin signaling and impaired responsiveness of adipose tissues to FGF21 may, at least in part, contribute to the overall picture of metabolic dysfunction after SCI.

Recent advances in understanding the role of leptin in energy homeostasis

The hormone leptin plays a critical role in energy homeostasis, although our overall understanding of acutely changing leptin levels still needs improvement. Several developments allow a fresh look at recent and early data on leptin action. This review highlights select recent publications that are relevant for understanding the role played by dynamic changes in circulating leptin levels. We further discuss the relevance for our current understanding of leptin signaling in central neuronal feeding and energy expenditure circuits and highlight cohesive and discrepant findings that need to be addressed in future studies to understand how leptin couples with physiological adaptations of food intake and energy expenditure.

Leptin and psychiatric illnesses: does leptin play a role in antipsychotic-induced weight gain?

Antipsychotic-induced weight gain is the most prevalent somatic adverse event occurring in patients treated by antipsychotics, especially atypical antipsychotics. It is of particular interest because of its repercussion on cardiovascular morbidity and mortality especially now that the use of second-generation antipsychotics has been extended to other mental health illnesses such as bipolar disorders and major depressive disorder. The mechanism underlying antipsychotics-induced weight gain is still poorly understood despite a significant amount of work on the topic. Recently, there has been an on-going debate of tremendous research interest on the relationship between antipsychotic-induced weight gain and body weight regulatory hormones such as leptin. Given that, researchers have brought to light the question of leptin's role in antipsychotic-induced weight gain. Here we summarize and discuss the existing evidence on the link between leptin and weight gain related to antipsychotic drugs, especially atypical antipsychotics.