Leptin regulation of core body temperature involves mechanisms independent of the thyroid axis

The Role of Selected Adipocytokines in Ovarian Cancer and Endometrial Cancer

Due to their multidirectional influence, adipocytokines are currently the subject of numerous intensive studies. Significant impact applies to many processes, both physiological and pathological. Moreover, the role of adipocytokines in carcinogenesis seems particularly interesting and not fully understood. For this reason, ongoing research focuses on the role of these compounds in the network of interactions in the tumor microenvironment. Particular attention should be drawn to cancers that remain challenging for modern gynecological oncology-ovarian and endometrial cancer. This paper presents the role of selected adipocytokines, including leptin, adiponectin, visfatin, resistin, apelin, chemerin, omentin and vaspin in cancer, with a particular focus on ovarian and endometrial cancer, and their potential clinical relevance.

Roles of leptin on energy balance and thermoregulation in Eothenomys miletus

Leptin is a hormone mainly synthesized and secreted by white adipose tissue (WAT), which regulates various physiological processes. To investigate the role of leptin in energy balance and thermoregulation in Eothenomys miletus, voles were randomly divided into leptin-injected and PBS-injected groups and placed at 25°C ± 1°C with a photoperiod of 12 L:12 D. They were housed under laboratory conditions for 28 days and compared in terms of body mass, food intake, water intake, core body temperature, interscapular skin temperature, resting metabolic rate (RMR), nonshivering thermogenesis (NST), liver and brown adipose tissue (BAT) thermogenic activity, and serum hormone levels. The results showed that leptin injection decreased body mass, body fat, food intake, and water intake. But it had no significant effect on carcass protein. Leptin injection increased core body temperature, interscapular skin temperature, resting metabolic rate, non-shivering thermogenesis, mitochondrial protein content and cytochrome C oxidase (COX) activity in liver and brown adipose tissue, uncoupling protein 1 (UCP1) content and thyroxin 5'-deiodinase (T₄5'-DII) activity in brown adipose tissue significantly. Serum leptin, triiodothyronine (T₃), thyrotropin-releasing hormone (TRH) and corticotropin-releasing hormone (CRH) concentrations were also increased significantly. Correlation analysis showed that serum leptin levels were positively correlated with core body temperature, body mass loss, uncoupling protein 1 content, thyroxin 5'-deiodinase activity, nonshivering thermogenesis, and negatively correlated with food intake; thyroxin 5'-deiodinase and triiodothyronine levels were positively correlated, suggesting that thyroxin 5'-deiodinase may play an important role in leptin-induced thermogenesis in brown adipose tissue. In conclusion, our study shows that exogenous leptin is involved in the regulation of energy metabolism and thermoregulation in E. miletus, and thyroid hormone may play an important role in the process of leptin regulating energy balance in E. miletus.

Mammalian tumor-like organs. 2. Mammalian adipose has many tumor features and obesity is a tumor-like process

BACKGROUND

In previous publications, the author developed the theory of carcino-evo-devo, which predicts that evolutionarily novel organs should recapitulate some features of tumors in their development.

MAIN TEXT

Mammalian adipose is currently recognized as a multi-depot metabolic and endocrine organ consisting of several adipose tissues. Although lipid-storing cells and proteins are ancient, the adipose organ as a whole is evolutionarily novel to mammals. The adipose expansion has remarkable similarities with the growth of solid tumors. These similarities are the following: (1) The capability to unlimited expansion; (2) Reversible plasticity; (3) Induction of angiogenesis; (4) Chronic inflammation; (5) Remodeling and disfunction; (6) Systemic influence on the organism; (7) Hormone production; (8) Production of miRNAs that influence other tissues; (9) Immunosuppression; (10) DNA damage and resistance to apoptosis; (11) Destructive infiltration in other organs and tissues. These similarities include the majority of "hallmarks of cancer". In addition, lipomas are the most frequent soft tissue tumors, and similar drugs may be used for the treatment of obesity and cancer by preventing infiltration. This raises the possibility that obesity, at least in part, may represent an oncological problem. The existing similarities between adipose and tumors suggest the possible evolutionary origin of mammalian adipose from some ancestral benign mesenchymal hereditary tumors. Indeed, using a transgenic inducible zebrafish tumor model, we described many genes, which originated in fish and were expressed in fish tumors. Their human orthologs LEP, NOTCH1, SPRY1, PPARG, ID2, and CIDEA acquired functions connected with the adipose organ. They are also involved in tumor development in humans.

CONCLUSION

If the hypothesis of the evolutionary origin of the adipose organ from the ancestral hereditary tumor is correct, it may open new opportunities to resolve the oncological problem and the problem of the obesity epidemic. New interventions targeting LEP, NOTCH1, SPRY1, PPARG, ID2, and CIDEA gene network, in addition to what already is going on, can be designed for treatment and prevention of both obesity and tumors.

Leptin counteracts hypothermia in hypothyroidism through its pyrexic effects and by stabilizing serum thyroid hormone levels

Objective

Thyroid hormones (TH) are essential for the homeostatic control of energy metabolism and the regulation of body temperature. The hypothalamic–pituitary–thyroid (HPT) axis is regulated by negative feedback mechanisms, ensuring that TH levels are maintained at a constant level. However, the feedback mechanisms underlying the resetting of the HPT axis regulation in the control of body temperature are still not fully understood. Here, we aimed to determine the thermoregulatory response in hypothyroid mice to different environmental temperatures and the underlying mechanisms.

Methods

Distinct thermogenic challenges were induced in hypothyroid female C57BL/6N and leptin-deficient ob/ob mice through housing at either room temperature or thermoneutrality. The thermogenic and metabolic effects were analyzed through metabolic chambers, 18F-FDG-PET/MRI, infrared thermography, metabolic profiling, histology, gene expression and Western blot analysis.

Results

In hypothyroid mice maintained at room temperature, high leptin serum levels induce a pyrexic effect leading to the stabilization of body temperature through brown adipose tissue thermogenesis and white adipose tissue browning. Housing at thermoneutrality leads to the normalization of leptin levels and a reduction of the central temperature set point, resulting in decreased thermogenesis in brown and white adipose tissue and skeletal muscle and a significant decline in body temperature. Furthermore, anapyrexia in hypothyroid leptin-deficient ob/ob mice indicates that besides its pyrexic actions, leptin exerts a stimulatory effect on the HPT axis to stabilize the remaining TH serum levels in hypothyroid mice.

Conclusion

This study led to the identification of a previously unknown endocrine loop in which leptin acts in concert with the HPT axis to stabilize body temperature in hypothyroid mice.

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Thyroid hormones are essential for the regulation of body temperature.

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Thyroid hormone-deficient (hypothyroid) mice show distinct leptin serum concentrations in response to changes in ambient housing temperature.

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High leptin serum levels confer a stimulatory effect on the hypothalamic-pituitary-thyroid axis.

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High leptin serum level prevents fall in body temperature in hypothyroid mice at room temperature through its pyrexic effects.

Leptin Improves Parameters of Brown Adipose Tissue Thermogenesis in Lipodystrophic Mice

Lipodystrophy syndromes (LD) are a heterogeneous group of very rare congenital or acquired disorders characterized by a generalized or partial lack of adipose tissue. They are strongly associated with severe metabolic dysfunction due to ectopic fat accumulation in the liver and other organs and the dysregulation of several key adipokines, including leptin. Treatment with leptin or its analogues is therefore sufficient to reverse some of the metabolic symptoms of LD in patients and in mouse models through distinct mechanisms. Brown adipose tissue (BAT) thermogenesis has emerged as an important regulator of systemic metabolism in rodents and in humans, but it is poorly understood how leptin impacts BAT in LD. Here, we show in transgenic C57Bl/6 mice overexpressing sterol regulatory element-binding protein 1c in adipose tissue (Tg (aP2-nSREBP1c)), an established model of congenital LD, that daily subcutaneous administration of 3 mg/kg leptin for 6 to 8 weeks increases body temperature without affecting food intake or body weight. This is associated with increased protein expression of the thermogenic molecule uncoupling protein 1 (UCP1) and the sympathetic nerve marker tyrosine hydroxylase (TH) in BAT. These findings suggest that leptin treatment in LD stimulates BAT thermogenesis through sympathetic nerves, which might contribute to some of its metabolic benefits by providing a healthy reservoir for excess circulating nutrients.

Decreased energy availability during training overload is associated with non-functional overreaching and suppressed ovarian function in female runners

Low energy availability (EA) suppresses many physiological processes, including ovarian function in female athletes. Low EA could also predispose athletes to develop a state of overreaching. This study compared the changes in ad libitum energy intake (EI), exercise energy expenditure (ExEE), and EA among runners completing a training overload (TO) phase. We tested the hypothesis that runners becoming overreached would show decreased EA, suppressed ovarian function and plasma leptin, compared with well-adapted (WA) runners. After 1 menstrual cycle (baseline), 16 eumenorrheic runners performed 4 weeks of TO followed by a 2-week recovery (131 ± 3% and 63 ± 6% of baseline running volume, respectively). Seven-day ExEE, EI, running performance (RUN_perf) and plasma leptin concentration were assessed for each phase. Salivary estradiol concentration was measured daily. Urinary luteinizing hormone concentration tests confirmed ovulation. Nine runners adapted positively to TO (WA, ΔRUN_perf: +4 ± 2%); 7 were non-functionally overreached (NFOR; ΔRUN_perf: -9 ± 2%) as RUN_perf remained suppressed after the recovery period. WA increased EI during TO, maintaining their baseline EA despite a large increase in ExEE (ΔEA = +1.9 ± 1.3 kcal·kg fat free mass (FFM)^-1·d^-1, P = 0.17). By contrast, NFOR showed no change in EI, leading to decreased EA (ΔEA = -5.6 ± 2.1 kcal·kg FFM^-1·d^-1, P = 0.04). Plasma leptin concentration mid-cycle and luteal salivary estradiol concentration decreased in NFOR only. Contrasting with WA, NFOR failed to maintain baseline EA during TO, resulting in poor performance outcomes and suppressed ovarian function. ClinicalTrials.gov no. NCT02224976. Novelty: Runners adapting positively to training overload (TO) increased ad libitum energy intake, maintaining baseline EA and ovarian function through TO. By contrast, NFOR runners failed to increase energy intake, showing suppressed EA and ovarian function during TO.

Behavioral, metabolic, and renal outcomes of 1-month isolation in adolescent male Dahl salt-sensitive rats

Social contact deficit is considered a stressful circumstance associated with various neural, hormonal, genetic, immune, and behavioral effects. A growing body of clinical and basic science evidence suggests that social isolation is linked to a higher risk of various neurological, cardiovascular, and metabolic diseases, including hypertension, diabetes mellitus, and obesity. However, the impact of the deficit of social interaction on kidney function is not well established. The Dahl salt-sensitive (SS) rat is a classical model of salt-induced hypertension and associated kidney injury. In this study, we investigated the effect of 30 days of social isolation (SI) on blood and urine electrolytes and metabolic, physiological, and behavioral parameters in adolescent male Dahl SS rats fed a normal 0.4% NaCl diet. SI rats demonstrated increased behavioral excitability compared with rats kept in groups. We also observed increased food consumption and a decrease in plasma leptin levels in the SI group without differences in water intake and weight gain compared with grouped animals. No changes in the level of blood and urine electrolytes, 24-h urine output, creatinine clearance, and albumin/creatinine ratio were identified between the SI and grouped rats. These findings indicate that 30 days of social isolation of adolescent Dahl SS rats affects metabolic parameters but has no apparent influence on kidney function.

Comparative gene expression profiling between optic nerve and spinal cord injury in Xenopus laevis reveals a core set of genes inherent in successful regeneration of vertebrate central nervous system axons

BACKGROUND

The South African claw-toed frog, Xenopus laevis, is uniquely suited for studying differences between regenerative and non-regenerative responses to CNS injury within the same organism, because some CNS neurons (e.g., retinal ganglion cells after optic nerve crush (ONC)) regenerate axons throughout life, whereas others (e.g., hindbrain neurons after spinal cord injury (SCI)) lose this capacity as tadpoles metamorphose into frogs. Tissues from these CNS regions (frog ONC eye, tadpole SCI hindbrain, frog SCI hindbrain) were used in a three-way RNA-seq study of axotomized CNS axons to identify potential core gene expression programs for successful CNS axon regeneration.

RESULTS

Despite tissue-specific changes in expression dominating the injury responses of each tissue, injury-induced changes in gene expression were nonetheless shared between the two axon-regenerative CNS regions that were not shared with the non-regenerative region. These included similar temporal patterns of gene expression and over 300 injury-responsive genes. Many of these genes and their associated cellular functions had previously been associated with injury responses of multiple tissues, both neural and non-neural, from different species, thereby demonstrating deep phylogenetically conserved commonalities between successful CNS axon regeneration and tissue regeneration in general. Further analyses implicated the KEGG adipocytokine signaling pathway, which links leptin with metabolic and gene regulatory pathways, and a novel gene regulatory network with genes regulating chromatin accessibility at its core, as important hubs in the larger network of injury response genes involved in successful CNS axon regeneration.

CONCLUSIONS

This study identifies deep, phylogenetically conserved commonalities between CNS axon regeneration and other examples of successful tissue regeneration and provides new targets for studying the molecular underpinnings of successful CNS axon regeneration, as well as a guide for distinguishing pro-regenerative injury-induced changes in gene expression from detrimental ones in mammals.

Leptin: Is It Thermogenic?

Animals that lack the hormone leptin become grossly obese, purportedly for 2 reasons: increased food intake and decreased energy expenditure (thermogenesis). This review examines the experimental evidence for the thermogenesis component. Analysis of the data available led us to conclude that the reports indicating hypometabolism in the leptin-deficient ob/ob mice (as well as in the leptin-receptor-deficient db/db mice and fa/fa rats) derive from a misleading calculation artefact resulting from expression of energy expenditure per gram of body weight and not per intact organism. Correspondingly, the body weight-reducing effects of leptin are not augmented by enhanced thermogenesis. Congruent with this, there is no evidence that the ob/ob mouse demonstrates atrophied brown adipose tissue or diminished levels of total UCP1 mRNA or protein when the ob mutation is studied on the inbred C57BL/6 mouse background, but a reduced sympathetic nerve activity is observed. On the outbred "Aston" mouse background, brown adipose tissue atrophy is seen, but whether this is of quantitative significance for the development of obesity has not been demonstrated. We conclude that leptin is not a thermogenic hormone. Rather, leptin has effects on body temperature regulation, by opposing torpor bouts and by shifting thermoregulatory thresholds. The central pathways behind these effects are largely unexplored.

Fibroblast Growth Factor-21, Leptin, and Adiponectin Responses to Acute Cold-Induced Brown Adipose Tissue Activation

BACKGROUND

Adipocyte-derived hormones play a role in insulin sensitivity and energy homeostasis. However, the relationship between circulating fibroblast growth factor 21 (FGF21), adipocytokines and cold-induced supraclavicular brown adipose tissue (sBAT) activation is underexplored.

OBJECTIVE

Our study aimed to investigate the relationships between cold-induced sBAT activity and plasma FGF21 and adipocytokines levels in healthy adults.

DESIGN

Nineteen healthy participants underwent energy expenditure (EE) and supraclavicular infrared thermography (IRT) within a whole-body calorimeter at baseline and at 2 hours post-cold exposure. 18F-fluorodeoxyglucose (18F-FDG) positron-emission tomography/magnetic resonance (PET/MR) imaging scans were performed post-cold exposure. PET sBAT mean standardized uptake value (SUV mean), MR supraclavicular fat fraction (sFF), anterior supraclavicular maximum temperature (Tscv max) and EE change (%) after cold exposure were used to quantify sBAT activity.

MAIN OUTCOME MEASURES

Plasma FGF21, leptin, adiponectin, and tumor necrosis factor alpha (TNFα) at baseline and 2 hours post-cold exposure. Body composition at baseline by dual-energy x-ray absorptiometry (DXA).

RESULTS

Plasma FGF21 and adiponectin levels were significantly reduced after cold exposure in BAT-positive subjects but not in BAT-negative subjects. Leptin concentration was significantly reduced in both BAT-positive and BAT-negative participants after cold exposure. Adiponectin concentration at baseline was positively strongly associated with sBAT PET SUV mean (coefficient, 3269; P = 0.01) and IRT Tscv max (coefficient, 6801; P  = 0.03), and inversely correlated with MR sFF (coefficient, -404; P  = 0.02) after cold exposure in BAT-positive subjects but not in BAT-negative subjects.

CONCLUSION

Higher adiponectin concentrations at baseline indicate a greater cold-induced sBAT activity, which may be a novel predictor for sBAT activity in healthy BAT-positive adults.

HIGHLIGHTS

A higher adiponectin concentration at baseline was associated with higher cold-induced supraclavicular BAT PET SUV mean and IRT Tscv max, and lower MR supraclavicular FF. Adiponectin levels maybe a novel predictor for cold-induced sBAT activity.

Rats that are predisposed to excessive obesity show reduced (leptin-induced) thermoregulation even in the preobese state

Both feeding behavior and thermogenesis are regulated by leptin. The sensitivity to leptin's anorexigenic effects on chow diet was previously shown to predict the development of diet-induced obesity. In this study, we determined whether the sensitivity to leptin's anorexigenic effects correlates with leptin's thermogenic response, and if this response is exerted at the level of the dorsomedial hypothalamus (DMH), a brain area that plays an important role in thermoregulation. Based on the feeding response to injected leptin on a chow diet, rats were divided into leptin-sensitive (LS) and leptin-resistant (LR) groups. The effects of leptin on core body, brown adipose tissue (BAT) and tail temperature were compared after intravenous versus intra-DMH leptin administration. After intravenous leptin injection, LS rats increased their BAT thermogenesis and reduced heat loss via the tail, resulting in a modest increase in core body temperature. The induction of these thermoregulatory mechanisms with intra-DMH leptin was smaller, but in the same direction as with intravenous leptin administration. In contrast, LR rats did not show any thermogenic response to either intravenous or intra-DMH leptin. These differences in the thermogenic response to leptin were associated with a 1°C lower BAT temperature and reduced UCP1 expression in LR rats under ad libitum feeding. The preexisting sensitivity to the anorexigenic effects of leptin, a predictor for obesity, correlates with the sensitivity to the thermoregulatory effects of leptin, which appears to be exerted, at least in part, at the level of the DMH.

Validation of an equation for energy expenditure that does not require the respiratory quotient

Background

Energy expenditure (EE) calculated from respirometric indirect calorimetry is most accurate when based on oxygen consumption (VO₂), carbon dioxide production (VCO₂) and estimated protein metabolism (PM). EE has a substantial dependence of ~7% on the respiratory quotient (RQ, VCO₂/VO₂) and a lesser dependence on PM, yet many studies have instead estimated EE from VO₂ only while PM has often been ignored, thus reducing accuracy. In 1949 Weir proposed a method to accurately calculate EE without using RQ, which also adjusts for estimated PM based on dietary composition. This RQ^- method utilizes the calorimeter airflow rate (FR), the change in fractional O₂ concentration (ΔFO₂) and the dietary protein fraction. The RQ^- method has not previously been empirically validated against the standard RQ⁺ method using both VO₂ and RQ. Our aim was to do that.

Methods

VO₂ and VCO₂ were measured repeatedly in 8 mice fed a high protein diet (HPD) during exposure to different temperatures (n = 168 measurements of 24h gas exchange). The HPD-adjusted RQ⁺ equation was: EE [kcal/time] = VO₂ [L/time]×(3.853+1.081RQ) while the corresponding RQ^- equation was: EE = 4.934×FR×ΔFO₂. Agreement was analyzed using the ratios of the RQ^- to RQ⁺ methods along with regression and Bland-Altman agreement analyses. We also evaluated the standard equation using the dietary food quotient (FQ) of 0.91 as a proxy for RQ (FQ⁺ method).

Results

Ratio analysis revealed that the mean error of the RQ^- method was only 0.11 ± 0.042% while the maximum error was only 0.21%. Error using the FQ⁺ method was 4 -and 10-fold greater, respectively. Bland-Altman analysis demonstrated that the RQ^- method very slightly overestimates EE as RQ decreases. Theoretically, this error can be eliminated completely by imposing an incurrent fractional oxygen concentration at a value only slightly greater than the atmospheric level.

Conclusions

The Weir ‘RQ-free’ method for calculating EE is a highly valid alternative to the ‘gold standard’ method that requires RQ. The RQ^- approach permits reduced cost and complexity in studies focused on EE and provides a way to rescue EE measurement in studies compromised by faulty CO₂ measurements. Practitioners of respirometry should consider adjusting EE calculations for estimated protein metabolism based on dietary composition.