Obesity Disrupts Rhythmic Clock Gene Expression in Maternal Adipose Tissue during Rat Pregnancy

Adipose tissue-liver cross-talk: a route to hepatic dysfunction in pregnant women with obesity

Obesity during pregnancy has been escalating, becoming a huge problem that poses consequences not only for the health of the offspring but also for the maternal well-being. Women's adipose and hepatic tissue metabolism undergoes significant changes during the gestational period. During pregnancy, obesity is a primary instigator of steatosis, increasing the risk of non-alcholic fatty liver disease (NAFLD), now recognized under the updated nomenclature metabolic dysfunction-associated steatotic liver disease (MASLD). Pregnant women with obesity present higher levels of free fatty acids and glucose, reduction in insulin sensitivity, and adipose tissue endocrine dysregulation. Furthermore, obesity-induced modifications in clock genes and lipid-associated gene expression within adipose tissue disrupt crucial metabolic adaptations, potentially culminating in adipose tissue dysfunction. Thus, the liver experiences increased exposure to free fatty acids through the portal vein. Higher uptake of free fatty acids into the liver disrupts hepatic lipid oxidation while enhances lipogenesis, thereby predisposing to ectopic fat deposition within the liver. This review focuses on the obesity-induced changes during pregnancy in both liver and adipose tissue metabolism, elucidating how the metabolic crosstalk between these two organs can be dysregulated in pregnant women living with obesity.

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.

Nuclear receptors, gestational metabolism and maternal metabolic disorders

Normal pregnancy is characterised by a gradual alteration in metabolism that results in elevated serum bile acids, dyslipidaemia and impaired glucose tolerance in the third trimester. Nuclear receptors play important roles in regulating metabolic pathways that influence alterations in these parameters. There is evidence for altered function of FXR and LXR in gestation; these nuclear receptors play an integral role in bile acid and lipid homeostasis. There is some evidence for influence of clock genes in late pregnancy metabolic changes, and this may be linked to alterations in placental gene expression and function, thereby influencing fetal growth. This article will review the current data from human studies and investigation of animal models to illustrate the role of nuclear receptors (namely LXR, FXR, PPARs and clock genes) in gestational alterations in metabolism and the ways this may influence susceptibility to metabolic disorders of pregnancy such as gestational diabetes mellitus and intrahepatic cholestasis of pregnancy.