Circadian Dysfunction and Obesity: Is Leptin the Missing Link?

Frozen Shoulder as a Metabolic and Immune Disorder: Potential Roles of Leptin Resistance, JAK-STAT Dysregulation, and Fibrosis

Frozen shoulder (FS) is a complex and multifactorial condition characterized by persistent inflammation, fibrosis, and metabolic dysregulation. Despite extensive research, the underlying drivers of FS remain poorly understood. Recent findings indicate the coexistence of pro-inflammatory and fibrosis-resolving macrophages within affected tissues, suggesting a dysregulated immune response influenced by metabolic and neuroendocrine factors. This review proposes that leptin resistance, a hallmark of metabolic syndrome and chronic inflammation, may play a central role in FS pathogenesis by impairing macrophage polarization, perpetuating inflammation, and disrupting fibrosis resolution. The JAK-STAT signaling pathway, critically modulated by leptin resistance, may further contribute to immune dysregulation by sustaining inflammatory macrophage activation and interfering with tissue remodeling. Additionally, FS shares pathogenic features with fibrotic diseases driven by TGF-β signaling, mitochondrial dysfunction, and circadian disruption, further linking systemic metabolic dysfunction to localized fibrotic pathology. Beyond immune and metabolic regulation, alterations in gut microbiota, bacterial translocation, and chronic psychosocial stress may further exacerbate systemic inflammation and neuroendocrine imbalances, intensifying JAK-STAT dysregulation and leptin resistance. By examining the intricate interplay between metabolism, immune function, and fibrotic remodeling, this review highlights targeting leptin sensitivity, JAK-STAT modulation, and mitochondrial restoration as novel therapeutic strategies for FS treatment. Future research should explore these interconnections to develop integrative interventions that address both the metabolic and immune dysregulation underlying FS, ultimately improving clinical outcomes.

Evaluating circadian light hygiene: Methodology and health implications

Background — A growing body of research demonstrates that a substantial daily range of light exposure, characterized by ample daylight followed by darkness during sleep, is essential for human well-being. This encompasses crucial aspects like sleep quality, mood regulation, and cardiovascular and metabolic health. Objective — This study characterizes Circadian Light Hygiene (CLH) as an essential factor in maintaining health, well-being, and longevity in modern society. CLH involves adjusting the 24-hour light exposure dynamic range to support the natural sleep-wake cycle and circadian rhythms. Three major challenges to CLH negatively impacting human health are: 1) light pollution (light at night, or LAN), characterized by excessive evening and nighttime artificial light; 2) insufficient natural daylight; and 3) irregular light exposure patterns. These interacting challenges necessitate a systematic approach to measurement and analysis. Material and Methods — A systematic review of peer-reviewed literature published through October 30, 2024, examined the methodologies and health effects of circadian and seasonal aspects of light exposure. Conclusion — This review elucidates fundamental principles of circadian light hygiene, synthesizing existing literature and our research to assess the benefits of adequate daylight, the risks of light at night, and adverse outcomes stemming from diminished light exposure range, mistimed light exposure, and irregular patterns. Novel indices for quantifying and optimizing circadian light hygiene are introduced.

The cross-talk between leptin and circadian rhythm signaling proteins in physiological processes: a systematic review

BACKGROUND

Today, modern lifestyles and disrupted sleep patterns cause circadian clock rhythm impairments that are associated with altered leptin levels, which subsequently affect a wide range of physiological processes and have significant health burdens on societies. Nevertheless, there has been no systematic review of circadian clock genes and proteins, leptin, and related signaling pathways.

METHODS

Accordingly, we systematically reviewed circadian clock proteins, leptin, and molecular mechanisms between them by searching Pubmed, Scopus, ProQuest, Web of Sciences, and Google Scholar until September 2022. After considering the inclusion and exclusion criteria, 20 animal studies were selected. The risk of bias was assessed in each study.

RESULTS

The results clarified the reciprocal interconnected relationship between circadian clock genes and leptin. Circadian clock genes regulate leptin expression and signaling via different mechanisms, such as CLOCK-BMAL1 heterodimers, which increase the expression of PPARs. PPARs induce the expression of C/EBPα, a key factor in upregulating leptin expression. CLOCK-BMAL1 also induces the expression of Per1 and Rev-erb genes. PER1 activates mTORC1 and mTORC1 enhances the expression of C/EBPα. In addition, REV-ERBs activate the leptin signaling pathway. Also, leptin controls the expression of circadian clock genes by triggering the AMPK and ERK/MAPK signaling pathways, which regulate the activity of PPARs. Moreover, the roles of these molecular mechanisms are elucidated in different physiological processes and organs.

CONCLUSIONS

Crosstalk between circadian clock genes and leptin and their affecting elements should be considered in the selection of new therapeutic targets for related disorders, especially obesity and metabolic impairments.

Hígado graso (parte 1): aspectos generales, epidemiología, fisiopatología e historia natural

El hígado graso no alcohólico (NAFLD) se define por la presencia de grasa o esteatosis en los hepatocitos y abarca un espectro que va desde la esteatosis simple, pasa por la esteatohepatitis no alcohólica (NASH) con inflamación y fibrosis, y finaliza en la cirrosis. Se considera una prevalencia mundial global cercana al 25% en la población general y se diagnóstica entre los 40 y 50 años, con variaciones respecto al sexo predominante y con diferencias étnicas (la población hispana es la más afectada). El hígado graso está asociado al síndrome metabólico (SM), y la obesidad se considera el principal factor de riesgo con su presencia y con su progresión. El hígado graso es un trastorno complejo y muy heterogéneo en su fisiopatología, que resulta de la interacción de múltiples elementos: factores genéticos, epigenéticos, ambientales, culturales, entre otros. Todo ello en conjunto lleva a incremento paulatino de grasa hepática, resistencia a la insulina y alteraciones hormonales y de la microbiota intestinal, lo que genera un daño hepatocelular a través de la formación de radicales libres de oxígeno y activación de la fibrogénesis hepática. La historia natural del hígado graso es dinámica: los pacientes con esteatosis simple tienen bajo riesgo de progresión a cirrosis, mientras que en los pacientes con NASH este riesgo se aumenta; sin embargo, el proceso puede ser reversible y algunas personas tendrán una mejoría espontánea. La fibrosis parece ser el determinante de la mortalidad global y de los desenlaces asociados a la enfermedad hepática; se considera que en todos los pacientes la fibrosis empeora una etapa cada 14 años y en NASH empeora en una etapa cada 7 años. Estudios previos concluyen que aproximadamente 20% de los casos de esteatosis simple progresan a NASH y que, de ellos, aproximadamente el 20% progresan a cirrosis, con presencia de hepatocarcinoma (HCC) en el 5% a 10% de ellos.

Physiological regulation of leptin as an integrative signal of reproductive readiness

Reproductive function is tightly regulated by both environmental and physiological factors. The adipose-derived hormone leptin has been identified as one such critical factor that relays information about peripheral energy availability to the centrally-governed HPG axis to ensure there is sufficient energy availability to support the high energy demands of mammalian reproduction. In the absence of adequate central leptin signaling, reproductive function is suppressed. While leptin levels are predominantly regulated by adiposity, circulating leptin levels are also under the modulatory influence of other factors, such as stress system activation, circadian rhythmicity, and immune activation and the inflammatory response. Furthermore, changes in leptin sensitivity can affect the degree to which leptin exerts its influence on the neuroendocrine reproductive axis. This review will discuss the different mechanisms by which leptin serves to integrate and relay information about metabolic, psychological, environmental and immune conditions to the central neuronal network that governs reproductive function.

Circadian Rhythm Disruption as a Contributor to Racial Disparities in Prostate Cancer

In the United States, African American (AA) men have a 2.4 times higher mortality rate due to prostate cancer than White men. The multifactorial causes of the racial disparities in prostate cancer involve various social determinants of health, socioeconomic status, and access to healthcare. However, emerging evidence also suggests that circadian rhythm disruption (CRD) contributes to prostate cancer, and AA men may be more susceptible to developing CRDs. Circadian rhythms play a significant role in metabolism, hormone secretion, and sleep/wake cycles. Disruption in these circadian rhythms can be caused by airplane travel/jetlag, night shift work, exposure to light, and neighborhood noise levels, which can contribute to sleep disorders and chronic conditions such as obesity, diabetes, cardiovascular disease, and depression. The drivers of the racial disparities in CRD include night shift work, racial discrimination, elevated stress, and residing in poor neighborhoods characterized by high noise pollution. Given the increased vulnerability of AA men to CRDs, and the role that CRDs play in prostate cancer, elucidating the clock-related prostate cancer pathways and their behavior and environmental covariates may be critical to better understanding and reducing the racial disparities in prostate cancer.

Recent evidence in support of traditional chinese medicine to restore normal leptin function in simple obesity

Reducing the incidence of obesity is the focus of global attention, and traditional Chinese medicine (TCM) may play an important role in achieving this goal. Numerous studies have shown that most individuals with obesity have leptin resistance, exogenous leptin is ineffective in individuals with obesity, and the effect of leptin decreases with increased serum leptin levels in individuals with obesity. At present, there are many hypotheses regarding the mechanism of leptin resistance, but there is no definite conclusion. TCM has a long history of treating obesity, and single and compound TCM is an effective obesity treatment method. However, TCM's mechanism of action is complex and resists further weight loss drug development. In the last decade, network pharmacology has become an important tool for exploring the mechanism of compound TCMs. In this study, we reviewed the interrelation between TCM obesity treatment and leptin resistance, and network pharmacology studies of TCM intervention in simple obesity revealed that their targets overlap with the leptin pathway. We also summarized TCM pairs that effectively interfere with leptin resistance and their related intervention mechanisms, providing targets for anti-obesity drug development.

Autonomic Nervous System in Obesity and Insulin-Resistance-The Complex Interplay between Leptin and Central Nervous System

The role of the autonomic nervous system in obesity and insulin-resistant conditions has been largely explored. However, the exact mechanisms involved in this relation have not been completely elucidated yet, since most of these mechanisms display a bi-directional effect. Insulin-resistance, for instance, can be caused by sympathetic activation, but, in turn, the associated hyperinsulinemia can activate the sympathetic branch of the autonomic nervous system. The picture is made even more complex by the implicated neural, hormonal and nutritional mechanisms. Among them, leptin plays a pivotal role, being involved not only in appetite regulation and glucose homeostasis but also in energy expenditure. The purpose of this review is to offer a comprehensive view of the complex interplay between leptin and the central nervous system, providing further insights on the impact of autonomic nervous system balance on adipose tissue and insulin-resistance. Furthermore, the link between the circadian clock and leptin and its effect on metabolism and energy balance will be evaluated.

Variants in Circadian Rhythm Gene Cry1 Interacts with Healthy Dietary Pattern for Serum Leptin Levels: a Cross-sectional Study

Circadian disruption causes obesity and other metabolic disorders. There is no research considering the role of Cryptochromes (Cry) 1 body clock gene and major dietary patterns on serum leptin level and obesity. We aimed to investigate the interaction between Cry1 circadian gene polymorphisms and major dietary patterns on leptin and obesity related measurements. This study was performed on 377 overweight and obese women. Mean age and body mass index (BMI) of study subjects were 36.64 ± 9.02 years and 30.81 ± 3.8 kg/m², respectively. Dietary assessment was done using a validated 147-item food frequency questionnaire. Cry1 rs2287161 were genotyped using polymerase chain reaction-restriction fragment length polymorphism. Generalized linear models were used for interaction analysis. Healthy and unhealthy dietary pattern (HDP and UDP, respectively) were extracted using factor analysis (principal component analysis). Our study revealed a significant higher weight (p = 0.003) and BMI (p = 0.042) in women carrying CC homozygote compared with G allele carriers. Moreover, our findings showed a significant gene-diet interaction between HDP and Cry1 rs2287161 on BMI (p = 0.034) and serum leptin level (p = 0.056) in which, BMI and serum leptin level were lower in subjects with CC genotype than in those with GG genotype while following HDP. This study suggests a significant interaction between Cry1 rs2287161 polymorphisms and HDP on BMI and serum leptin and the lowering effects were apparent among C allele carriers compared to G allele ones. This data highlights the role of dietary pattern in relation of gene and obesity.

Unraveling the Role of Leptin in Liver Function and Its Relationship with Liver Diseases

Since its discovery twenty-five years ago, the fat-derived hormone leptin has provided a revolutionary framework for studying the physiological role of adipose tissue as an endocrine organ. Leptin exerts pleiotropic effects on many metabolic pathways and is tightly connected with the liver, the major player in systemic metabolism. As a consequence, understanding the metabolic and hormonal interplay between the liver and adipose tissue could provide us with new therapeutic targets for some chronic liver diseases, an increasing problem worldwide. In this review, we assess relevant literature regarding the main metabolic effects of leptin on the liver, by direct regulation or through the central nervous system (CNS). We draw special attention to the contribution of leptin to the non-alcoholic fatty liver disease (NAFLD) pathogenesis and its progression to more advanced stages of the disease as non-alcoholic steatohepatitis (NASH). Likewise, we describe the contribution of leptin to the liver regeneration process after partial hepatectomy, the mainstay of treatment for certain hepatic malignant tumors.

Leptin: Master Regulator of Biological Functions that Affects Breathing

Obesity is a global epidemic in developed countries accounting for many of the metabolic and cardiorespiratory morbidities that occur in adults. These morbidities include type 2 diabetes, sleep-disordered breathing (SDB), obstructive sleep apnea, chronic intermittent hypoxia, and hypertension. Leptin, produced by adipocytes, is a master regulator of metabolism and of many other biological functions including central and peripheral circuits that control breathing. By binding to receptors on cells and neurons in the brainstem, hypothalamus, and carotid body, leptin links energy and metabolism to breathing. In this comprehensive article, we review the central and peripheral locations of leptin's actions that affect cardiorespiratory responses during health and disease, with a particular focus on obesity, SDB, and its effects during early development. Obesity-induced hyperleptinemia is associated with centrally mediated hypoventilation with decrease CO₂ sensitivity. On the other hand, hyperleptinemia augments peripheral chemoreflexes to hypoxia and induces sympathoexcitation. Thus, "leptin resistance" in obesity is relative. We delineate the circuits responsible for these divergent effects, including signaling pathways. We review the unique effects of leptin during development on organogenesis, feeding behavior, and cardiorespiratory responses, and how undernutrition and overnutrition during critical periods of development can lead to cardiorespiratory comorbidities in adulthood. We conclude with suggestions for future directions to improve our understanding of leptin dysregulation and associated clinical diseases and possible therapeutic targets. Lastly, we briefly discuss the yin and the yang, specifically the contribution of relative adiponectin deficiency in adults with hyperleptinemia to the development of metabolic and cardiovascular disease. © 2020 American Physiological Society. Compr Physiol 10:1047-1083, 2020.

Novel insights into the spatial and temporal complexity of hypothalamic organization through precision methods allowing nanoscale resolution

The mammalian hypothalamus contains an astounding heterogeneity of neurons to achieve its role in coordinating central responses to virtually any environmental stressor over the life-span of an individual. Therefore, while core features of intrahypothalamic neuronal modalities and wiring patterns are stable during vertebrate evolution, integration of the hypothalamus into hierarchical brain-wide networks evolved to coordinate its output with emotionality, cognition and conscious decision-making. The advent of single-cell technologies represents a recent milestone in the study of hypothalamic organization by allowing the dissection of cellular heterogeneity and establishing causality between opto- and chemogenetic activity modulation of molecularly-resolved neuronal contingents and specific behaviours. Thus, organizational rules to accumulate an unprecedented variety of hierarchical neuroendocrine command networks into a minimal brain volume are being unravelled. Here, we review recent understanding at nanoscale resolution on how neuronal heterogeneity in the mammalian hypothalamus underpins the diversification of hormonal and synaptic output and keeps those sufficiently labile for continuous adaptation to meet environmental demands. Particular emphasis is directed towards the dissection of neuronal circuitry for aggression and food intake. Mechanistic data encompass cell identities, synaptic connectivity within and outside the hypothalamus to link vegetative and conscious levels of innate behaviours, and context- and circadian rhythm-dependent rules of synaptic neurophysiology to distinguish hypothalamic foci that either tune the body's metabolic set-point or specify behaviours. Consequently, novel insights emerge to explain the evolutionary advantages of non-laminar organization for neuroendocrine circuits coincidently using fast neurotransmitters and neuropeptides. These are then accrued into novel therapeutic principles that meet therapeutic criteria for human metabolic diseases.

Regulation of the MAPK signaling pathway by miR-421-5p in rats under light pollution

The present study aimed to explore the difference in the expression profiles of ovarian microRNA sequences in rats in a light pollution environment and rats in a normal light environment. Rats in the control group were exposed to 12‑h light/dark cycles, while rats in the model group were continuously exposed to 24‑h light. The ovaries were extracted from the two groups of rats, and Illumina HiSeq 2500 high‑throughput sequencing technology was used to detect the differences in microRNA (miRNA) expression among the two groups. Fluorescence quantitative reverse transcription‑polymerase chain reaction was used to verify the differential expression of miRNA. The present study was designed to experimentally validate the interaction between miR‑421‑5p and mitogen‑activated protein kinase (MAPK) 7 by using the dual‑luciferase reporter system, and to explore the expression of proteins in the MAPK signaling pathway with a lentiviral vector‑mediated small hairpin RNA interference against microRNA‑421‑5p. The expression of 45 miRNAs was significantly different. In total, 13 miRNAs were upregulated, of which 5 miRNA sequences were known and 8 were predicted. Furthermore, 32 miRNAs were downregulated, of which 11 miRNA sequences were known and 21 were predicted. The results of the luciferase reporter assay confirmed the targeting association between miR‑421‑5p and MAPK7. The expression levels of MAPK and genes in its downstream signaling pathways, including c‑Fos, CREB and c‑Myc, were downregulated when miR‑421‑5p was overexpressed and upregulated when miR‑421‑5p was silenced. The differential expression of miRNAs may serve an important role in the development of the ovary in a light pollution environment. miR‑421‑5p may regulate ovarian growth and development by targeting the MAPK signaling pathway in light polluted rat ovaries.

Dark matters: effects of light at night on metabolism

Life on earth has evolved during the past several billion years under relatively bright days and dark night conditions. The wide-spread adoption of electric lights during the past century exposed animals, both human and non-human, to significant light at night for the first time in their evolutionary history. Endogenous circadian clocks depend on light to entrain to the external daily environment and seasonal rhythms depend on clear nightly melatonin signals to assess time of year. Thus, light at night can derange temporal adaptations. Indeed, disruption of naturally evolved light-dark cycles results in several physiological and behavioural changes with potentially serious implications for physiology, behaviour and mood. In this review, data from night-shift workers on their elevated risk for metabolic disorders, as well as data from animal studies will be discussed. Night-shift workers are predisposed to obesity and dysregulated metabolism that may result from disrupted circadian rhythms. Although studies in human subjects are correlative, animal studies have revealed several mechanisms through which light at night may exert its effects on metabolism by disrupting circadian rhythms that are associated with inflammation, both in the brain and in the periphery. Disruption of the typical timing of food intake is a key effect of light at night and subsequent metabolic dysregulation. Strategies to avoid the effects of light at night on body mass dysregulation should be pursued.

Nobiletin protects against insulin resistance and disorders of lipid metabolism by reprogramming of circadian clock in hepatocytes

SCOPE

Circadian clock plays a principal role in orchestrating our daily physiology and metabolism, and their perturbation can evoke metabolic diseases such as fatty liver and insulin resistance. Nobiletin (NOB) has been demonstrated to possess antitumor and neuroprotective activities. The objective of the current study is to determine potential effects of NOB on modulating the core clock gene Bmal1 regarding ameliorating glucolipid metabolic disorders.

RESULTS

Our results revealed that NOB partially reverse the relatively shallow daily oscillations of circadian clock genes and reset phase-shifting circadian rhythms in primary hepatocytes under metabolic disorders conditions. Importantly, NOB was found to be effective at amplifying glucose uptake via stimulating IRS-1/AKT signaling pathway, as well as blunting palmitate-induced lipogenesis in HepG2 cells via modulating AMPK-Sirt1 signaling pathway and key enzymes of de novo lipogenesis in a Bmal1-dependent manner. NOB attenuated palmitate-stimulated excessive secretions of ROS, restored the depletions of mitochondrial membrane potential, which is similar to the recovery in expressions of mitochondrial respiration complex I-IV.

CONCLUSION

This study is the first to provide compelling evidences that NOB prevent cellular glucolipid metabolic imbalance and mitochondrial function in a Bmal1-dependent manner. Overall, NOB may serve as a nutritional preventive strategy in recovering metabolic disorders relevant to circadian clock.

Nutrigenetics and Nutrimiromics of the Circadian System: The Time for Human Health

Even though the rhythmic oscillations of life have long been known, the precise molecular mechanisms of the biological clock are only recently being explored. Circadian rhythms are found in virtually all organisms and affect our lives. Thus, it is not surprising that the correct running of this clock is essential for cellular functions and health. The circadian system is composed of an intricate network of genes interwined in an intrincated transcriptional/translational feedback loop. The precise oscillation of this clock is controlled by the circadian genes that, in turn, regulate the circadian oscillations of many cellular pathways. Consequently, variations in these genes have been associated with human diseases and metabolic disorders. From a nutrigenetics point of view, some of these variations modify the individual response to the diet and interact with nutrients to modulate such response. This circadian feedback loop is also epigenetically modulated. Among the epigenetic mechanisms that control circadian rhythms, microRNAs are the least studied ones. In this paper, we review the variants of circadian-related genes associated to human disease and nutritional response and discuss the current knowledge about circadian microRNAs. Accumulated evidence on the genetics and epigenetics of the circadian system points to important implications of chronotherapy in the clinical practice, not only in terms of pharmacotherapy, but also for dietary interventions. However, interventional studies (especially nutritional trials) that include chronotherapy are scarce. Given the importance of chronobiology in human health such studies are warranted in the near future.