PPARα mediates night neon light-induced weight gain: role of lipid homeostasis

PPARα suppresses low-intensity-noise-induced body weight gain in mice: the activated HPA axis plays an critical role

BACKGROUND

As the second most risky environmental pollution, noise imposes threats to human health. Exposure to high-intensity noise causes hearing impairment, psychotic disorders, endocrine modifications. The relationship among low-intensity noise, obesity and lipid-regulating nuclear factor PPARα is not yet clear.

METHODS

In this study, male wild-type (WT) and Pparα-null (KO) mice on a high-fat diet (HFD) were exposed to 75 dB noise for 12 weeks to explore the effect of low-intensity noise on obesity development and the role of PPARα. 3T3-L1 cells were treated with dexamethasone (DEX) and sodium oleate (OA) to verify the down-stream effect of hypothalamic-pituitary-adrenal (HPA) axis activation on the adipose tissues.

RESULTS

The average body weight gain (BWG) of WT mice on HFD exposed to noise was inhibited, which was not observed in KO mice. The mass and adipocyte size of adipose tissues accounted for the above difference of BWG tendency. In WT mice on HFD, the adrenocorticotropic hormone level was increased by the noise challenge. The aggravation of fatty liver by noise exposure occurred in both mouse lines, and the transport of hepatic redundant lipid to adipose tissues were similar. The lipid metabolism in adipose tissue driven by HPA axis accorded with the BWG inhibition in vivo, validated in 3T3-L1 adipogenic stem cells.

CONCLUSION

Chronic exposure to low-intensity noise aggravated fatty liver in both WT and KO mice. BWG inhibition was observed only in WT mice, which covered up the aggravation of fatty liver by noise exposure. PPARα mediates the activation of HPA axis by noise exposure in mice on HFD. Elevated adrenocorticotropic hormone (ACTH) promoted lipid metabolism in adipocytes, which contributed to the disassociation of BWG and fatty liver development in male WT mice. Summary of PPARα suppresses noise-induced body weight gain in mice on high-fat-diet. Chronic exposure to low-intensity noise exposure inhibited BWG by PPARα-dependent activation of the HPA axis.

Depression Exacerbates Hepatic Steatosis in C57BL/6J Mice by Activating the Hypothalamic-Pituitary-Adrenal Axis

BACKGROUND/AIM

Depression is associated with metabolic disorders, including non-alcoholic fatty liver disease (NAFLD). However, the mechanisms underlying the interaction between them are still poorly known.

MATERIALS AND METHODS

In this study, mice on a choline deficiency, L-amino acid-defined, high-fat diet (CDAHFD) developing steatosis were challenged with chronic restraint stress (CRS), a protocol widely used to induce depression. The development of depression and steatosis was evaluated using histopathology analysis, ELISA, q-PCR and Western Blot.

RESULTS

The contribution of the activated HPA axis to hepatic steatosis progress was fully established, which was validated using a hepatocyte model. Histopathological and biochemical analysis indicated that steatosis was exacerbated by CRS challenge, and behavioral tests indicated that the mice developed depression. Among the screened endocrinal pathways, the hypothalamic-pituitary-adrenal (HPA) axis was significantly activated and the synergistic effect of CDAHFD and CRS in activating the HPA axis was observed. In the hypothalamus, expression of corticotropin-releasing hormone (CRH) was increased by 86% and the protein levels of hypothalamic CRH were upregulated by 25% to 33% by CRS treatment. Plasma CRH levels were elevated by 45-56% and plasma adrenocorticotropic hormone (ACTH) levels were elevated by 29-58% by CRS treatment. In the liver, target genes of the HPA axis were activated, accompanied by disruption of the lipid metabolism and progression of steatohepatitis. The lipid metabolism in the Hepa1-6 cell line treated with endogenous corticosterone (CORT) was in accordance with the aforementioned in vivo responses.

CONCLUSION

Depression aggravated hepatic steatosis in CDAHFD-fed mice by activating the HPA axis. The risk of NAFLD development should be fully considered in depressive patients and improvement of psychotic disorders could be an etiological treatment strategy for them.

A CDAHFD-induced mouse model mimicking human NASH in the metabolism of hepatic phosphatidylcholines and acyl carnitines

Non-alcoholic steatohepatitis (NASH) is the hepatic manifestation of a cluster of conditions associated with lipid metabolism disorders. Ideal animal models mimicking the human NASH need to be explored to better understand the pathogenesis. A choline-deficient, L-amino acid-defined, high-fat diet (CDAHFD) has recently been used to induce the NASH model, but the advantages are not established. NASH models were induced using the well-known traditional methionine- and choline-deficient (MCD) diet for 5 weeks and the recently used CDAHFD for 3 weeks. Liver phenotypes were analyzed to evaluate the differences in markers related to NASH. Lipidomics and metabolism analyses were used to investigate the effects of dietary regimens on the lipidome of the liver. The CDAHFD induced stronger NASH responses than the MCD, including lipid deposition, liver injury, inflammation, bile acid overload and hepatocyte proliferation. A significant difference in the hepatic lipidome was revealed between the CDAHFD and MCD-induced NASH models. In particular, the CDAHFD reduced the hepatic levels of phosphatidylcholines (PCs) and acylcarnitines (ACs), which was supported by the metabolism analysis and in line with the tendency of human NASH. Pathologically, the CDAHFD could effectively induce a more human-like NASH model over the traditional MCD. The hepatic PCs, ACs and their metabolism in CDAHFD-treated mice were down-regulated, similar to those in human NASH.

Molecular mechanisms of artificial light at night affecting circadian rhythm disturbance

Artificial light at night (ALAN) pollution has been regarded as a global environmental concern. More than 80% of the global population is exposed to light pollution. Exacerbating this issue, artificially lit outdoor areas are growing by 2.2% per year, while continuously lit areas have brightened by 2.2% each year due to rapid population growth and expanding urbanization. Furthermore, the increasing prevalence of night shift work and smart device usage contributes to the inescapable influence of ALAN. Studies have shown that ALAN can disrupt endogenous biological clocks, resulting in a disturbance of the circadian rhythm, which ultimately affects various physiological functions. Up until now, scholars have studied various disease mechanisms caused by ALAN that may be related to the response of the circadian system to light. This review outlines the molecular mechanisms by which ALAN causes circadian rhythm abnormalities in sleep disorders, endocrine diseases, cardiovascular disease, cancer, immune impairment, depression, anxiety and cognitive impairments.

Exposure to low-intensity noise exacerbates nonalcoholic fatty liver disease by activating hypothalamus pituitary adrenal axis

Noise exposure induces metabolic disorders, in a latent, chronic and complex way. However, there is no direct evidence elucidating the relationship between low-intensity noise exposure and nonalcoholic fatty liver disease (NAFLD). Male mice (n = 5) on high-fat diet (HFD) were exposed to an average of 75 dB SPL noise for 3 months to reveal the effect of noise exposure on NAFLD, where the potential mechanisms were explored. In vivo (n = 5) and in vitro models challenged with dexamethasone (DEX) were used to verify the role of hypothalamus pituitary adrenal (HPA) axis activation in hepatic lipid metabolism. Typical chronic-restraint stress (CRS, n = 8) was used to explore the role of depression in modifying activity of HPA axis. Finally, animal experiment (n = 8) was repeated to validate the roles of depression and HPA axis activation in NAFLD development. Chronic low-intensity noise exposure exacerbated NAFLD in mice on HFD characterized by hepatocyte steatosis, modified lipid metabolism and inflammation level. Plasma ACTH in H + N group was 1.5-fold higher than that in HFD group. Transcription of glucocorticoid receptor target genes was increased by chronic low-intensity noise exposure in HFD-treated mice. Excessive glucocorticoids mimicking HPA axis activation induced NAFLD in vivo and in vitro. Plasma ACTH increase and lipid storage also occurred in depressive mice stressed by CRS. More interestingly, the same noise exposure simultaneously induced depression in mice, disrupted the HPA axis homeostasis and exacerbated NAFLD in a repeated experiment. Thus, three-month exposure to 75 dB SPL noise was sufficient to exacerbate NAFLD progress in mice, where activation of HPA axis played a critical role. Depression played an intermediate role and contributed to HPA axis activation up-stream of the exacerbation.

Association of outdoor artificial light at night with metabolic syndrome and the modifying effect of tree and grass cover

BACKGROUND

Epidemiological studies show that outdoor artificial light at night (ALAN) is linked to metabolic hazards, but its association with metabolic syndrome (MetS) remains unclear. We aimed to investigate the association of outdoor ALAN with MetS in middle-aged and elderly Chinese.

METHODS

From 2017-2020, we conducted a cross-sectional study in a total of 109,452 participants living in ten cities of eastern China. MetS was defined by fasting blood glucose (FG), triglyceride (TG), high-density lipoprotein cholesterol (HDL-C), blood pressure (BP), and waist circumference (WC). In 2021, we followed up 4395 participants without MetS at the baseline. Each participant's five-year average exposure to outdoor ALAN, as well as their exposure to green space type, were measured through matching to their address. Generalized linear models were used to assess the associations of outdoor ALAN with MetS. Stratified analyses were performed by sex, age, region, physical activity, and exposure to green space.

RESULTS

In the cross-sectional study, compared to the first quantile (Q1) of outdoor ALAN exposure, the odds ratios (ORs) of MetS were 1.156 [95 % confidence interval (CI): 1.111-1.203] and 1.073 (95 %CI: 1.021-1.128) respectively in the third and fourth quantiles (Q3, Q4) of outdoor ALAN exposure. The follow-up study found that, compared to the first quantile (Q1) of outdoor ALAN exposure, the OR of MetS in Q4 of ALAN exposure was 1.204 (95 %CI: 1.019-1.422). Adverse associations of ALAN with MetS components, including high FG, high TG, and obesity, were also found. Greater associations of ALAN with MetS were found in males, the elderly, urban residents, those with low frequency of physical activity, and those living in areas with low levels of grass cover and tree cover.

CONCLUSIONS

Outdoor ALAN exposure is associated with an increased MetS risk, especially in males, the elderly, urban residents, those lacking physical activity, and those living in lower levels of grass cover and tree cover.

Maternal circadian disruption before pregnancy impairs the ovarian function of female offspring in mice

Circadian disturbance brought on by shift employment, nighttime light pollution, and other factors is quite prevalent in contemporary culture. However, the effect of maternal circadian disruption before pregnancy on the reproduction of offspring in mice requires further research. Herein, we exposed female ICR mice to constant light to establish a model of preconceptional circadian disruption and then checked the ovarian function of female offspring (named the CLE group below). Our results revealed obesity, abnormal lipid metabolism and earlier puberty onset in the CLE group. Additionally, impaired ovarian follicle development, oocyte quality and preimplantation embryo development were shown in the CLE group. Moreover, the expression levels of Gnrh1 in the hypothalamus and Cyp17a1, Bmper, Bdnf and Lyve1 in ovaries, as well as circadian clock genes, including Clock, Cry1, Nr1d2 and Per2, were significantly downregulated in the CLE group. Mechanistically, immune responses, including the interleukin-17 (IL-17) signalling pathway, cytokine-cytokine receptor interaction and the chemokine signalling pathway, were altered in the CLE group, which may be responsible for the damaged ovarian function.

Down-regulation of hepatic CLOCK by PPARα is involved in inhibition of NAFLD

This work aimed to investigate the role of nuclear factor peroxisome proliferator-activated receptor α (PPARα) in modification of circadian clock and their relevance to development of nonalcoholic fatty liver disease (NAFLD). Both male wild-type (WT) and Pparα-null (KO) mice treated with high-fat diet (HFD) were used to explore the effect of PPARα and lipid diet on the circadian rhythm. WT, KO, and PPARα-humanized (hPPARα) mice were treated with PPARα agonist fenofibrate to reveal the hPPARα dependence of circadian locomotor output cycles kaput (CLOCK) down-regulation. The mouse model and hepatocyte experiments were designed to verify the action of PPARα in down-regulating CLOCK and lipid accumulation in vivo and in vitro. Strongest NAFLD developed in mice fed 45%HFD, and it was inhibited in WT mice. The activity rhythm of WT mice was found to be different from that of the KO mice on normal diet and HFD. The core circadian factor CLOCK was down-regulated by HFD in both WT and KO mice in the liver, not in the hypothalamus. More interestingly, hepatic CLOCK was down-regulated by basal PPARα and activated PPARα in dose dependence of fenofibrate. Accordingly, CLOCK down-regulation dependent of PPARα activity was involved in inhibition of lipid metabolism in hepatocytes. Down-regulation of hepatic CLOCK by basal PPARα contributes to tolerance against development of NAFLD. Inhibition of CLOCK by activated PPARα is involved in inhibition of NAFLD by PPARα agonists. KEY MESSAGES: • PPARα inhibited NAFLD development induced by HFD. • PPARα mediated modifications of circadian rhythm and the hepatic circadian factor CLOCK in NAFLD models. • Down-regulation of hepatic CLOCK by basal PPARα contributed to tolerance against development of NAFLD. • Inhibition of CLOCK by activated PPARα was involved in therapeutic actions against fatty liver diseases by PPARα agonists.

The role of light pollution in mammalian metabolic homeostasis and its potential interventions: A critical review

Irregular or unnatural artificial light causes severe environmental stress on the survival and health of organisms, which is rapidly becoming a widespread new type of environmental pollution. A series of disruptive behaviors to body homeostasis brought about by light pollution, including metabolic abnormalities, are likely to be the result of circadian rhythm disturbances. Recently, the proposed role of light pollution in metabolic dysregulation has accelerated it into an emerging field. Hence, the regulatory role of light pollution in mammalian metabolic homeostasis is reviewed in this contribution. Light at night is the most widely affected type of light pollution, which disrupts metabolic homeostasis largely due to its disruption of daily food intake patterns, alterations of hormone levels such as melatonin and glucocorticoids, and changes in the rhythm of inflammatory factor production. Besides, light pollution impairs mammalian metabolic processes in an intensity-, photoperiod-, and wavelength-dependent manner, and is also affected by species, gender, and diets. Nevertheless, metabolic disorders triggered by light pollution are not irreversible to some extent. Potential interventions such as melatonin supplementation, recovery to the LD cycle, time-restricted feeding, voluntary exercise, wearing blue light-shied goggles, and bright morning light therapy open a bright avenue to prevent light pollution. This work will help strengthen the relationship between light information and metabolic homeostasis and provide new insights for the better prevention of metabolic disorders and light pollution.

Monochromatic blue light not green light exposure is associated with continuous light-induced hepatic steatosis in high fat diet fed-mice via oxidative stress

Irregular light exposure is a newly identified environmental factor for the progression of lipid metabolism; however, the specific effect of light color exposure on lipid homeostasis remains unknown. Herein, 4-week-old male C57BL/6 J mice (n = 12) fed a high-fat diet (HFD) were exposed to a standard 12-h light: 12-h dark cycle (LD-WF) and a 24-h continuous monochromatic blue light (LL-BF), green light (LL-GF), or white light (LL-WF) condition for 12 weeks. LL-BF interfered with the expression of circadian genes in the hypothalamus and upregulated the plasma corticosterone (CORT) levels (p < 0.05) compared with LD-WF. Along with elevation of the CORT level, LL-BF enhanced glucocorticoid receptor synthesis, increased the Hsp90 mRNA level, reduced the antioxidant capacity, increased the production of ROS and MDA, and reduced the Pgc-1α mRNA level in the liver (p < 0.05). Furthermore, LL-BF disrupted the hepatic expression levels of genes involved in lipid metabolism, Acc and Hl, which further aggravated the hepatic steatosis status and significantly increased the liver pathological scores, TG, TC, IL-6, and TNF-α levels (p < 0.05). LL-BF consistently increased the body weight and incidence of dyslipidemia and lipid deposition. However, no difference was observed between LL-BF and LL-WF (p > 0.05). Surprisingly, LL-GF did not show any changes induced by LL-BF and LL-WF, and contrary to LL-BF, LL-GF and LD-WF showed no significantly differing changes (p > 0.05). Taken together, exposure to monochromatic blue light but not green light is associated with continuous light-aggravated hepatic steatosis in HFD-fed mice. The effect of continuous blue light exposure may be attributed to the disturbance of biological rhythm, increase in CORT secretion, induction of oxidative stress, and interference of the Acc and Hl levels in the liver.

Diurnal rhythms and obesity

PURPOSE OF REVIEW

This review will discuss the recent studies that implicate disturbed diurnal rhythms with the development of obesity. The second part of the review will discuss studies that use feeding time to restore diurnal rhythms and rescue obesity.

RECENT FINDINGS

Studies in patients with obesity and diabetes reveal attenuated circadian and metabolic rhythms in adipose tissue. The use of animal models furthers our mechanistic insight on how environmental disturbances such as high-fat diet and shift work disturb circadian and metabolic rhythms. Studies in both animals and humans describe how disturbance of diurnal rhythms can lead to increased adiposity and obesity. The effects of time-restricted feeding in animals and the time of feeding in humans provide new evidence on how restoring diurnal rhythms can reverse adiposity and obesity.

SUMMARY

Many more studies in humans were performed in recent years to confirm a number of findings from animal studies. It is becoming apparent that the time of feeding and maintaining a healthy daily schedule is important for metabolic health. Ongoing studies may soon improve current recommendations regarding the time of eating and time of day behavior.