Leptin Receptor Mediates Bmal1 Regulation of Estrogen Synthesis in Granulosa Cells

Abstract

Simple SummaryThere is increased interest in determining the effect of the biological clock system on reproduction, but how this biological system affects mammalian fertility and the regulation by clock genes on key genes of reproduction is poorly understood. This study examined the function of Leptin on reproduction through interaction with the Leptin receptor (Lepr) and the regulation of the key clock gene brain and muscle ARNT-like 1 (Bmal1) on Lepr. The results suggested that estrogen (E2) synthesis is regulated by Bmal1 through the Leptin–Lepr pathway as part of the regulatory mechanism of the circadian system on the fertility of female mammals.AbstractChronobiology affects female fertility in mammals. Lepr is required for leptin regulation of female reproduction. The presence of E-box elements in the Lepr promoter that are recognized and bound by clock genes to initiate gene transcription suggested that circadian systems might regulate fertility through Lepr. However, it is unclear whether Bmal1, a key oscillator controlling other clock genes, is involved in leptin regulation in hormone synthesis through Lepr. In this study, serum estradiol (E2) concentration and the expressions of Bmal1, Lepr, Cyp19a1, and Cyp11a1 genes were found to display well-synchronized circadian rhythms. Knockdown of Bmal1 significantly reduced expression levels of Lepr, Fshr, and Cyp19a1 genes; protein production of Bmal1, Lepr, and Cyp19a1; and the E2 concentration in granulosa cells. Knockdown of Lepr reduced the expression levels of Cyp19a1 and Cyp11a1 genes and Cyp19a1 protein, and also reduced E2 concentration. Addition of leptin affected the expression of Cyp19a1, Cyp11a1, and Fshr genes. Bmal1 deficiency counteracted leptin-stimulated upregulation of the genes encoding E2 synthesis in granulosa cells. These results demonstrated that Bmal1 participates in the process by which leptin acts on Lepr to regulate E2 synthesis.

Disruption of Circadian Rhythms: A Crucial Factor in the Etiology of Infertility

“…Interestingly, Bmal1 knockout mice showed a reduced expression of LepR and its ligand, reducing also estrogens concentration in granulosa cells. These results suggest that estrogens synthesis is regulated by Bmal1 through the Leptin-LepR pathway [96].…”

Critical Roles of the Circadian Transcription Factor BMAL1 in Reproductive Endocrinology and Fertility

“…BMAL1 knockdown by small interfering RNA (siRNA) in in vitro cultured porcine granulosa cells and luteinizing granulosa cells of rat and human, also led to a decrease in progesterone and estradiol synthesis ( 21 , 77 , 78 ). Additionally, evidence suggests that leptin and leptin receptor ( Lepr ) exerted positive effects on estradiol synthesis in murine granulosa cells, whereas BMAL1 knockdown reduced estradiol synthesis and suppressed the stimulating effect of leptin and lepr on estradiol synthesis and associated gene expressions ( 20 ). Therefore, BMAL1 plays a role in the process by which leptin signaling induces estradiol synthesis ( 20 ).…”

“…Additionally, evidence suggests that leptin and leptin receptor ( Lepr ) exerted positive effects on estradiol synthesis in murine granulosa cells, whereas BMAL1 knockdown reduced estradiol synthesis and suppressed the stimulating effect of leptin and lepr on estradiol synthesis and associated gene expressions ( 20 ). Therefore, BMAL1 plays a role in the process by which leptin signaling induces estradiol synthesis ( 20 ). Another hormone, prostaglandin E2 (PGE2), was also found to be reduced in the reproductive tissues of female BMAL1- KO mice ( 21 , 79 ).…”

“…In line with the impaired steroidogenesis, BMAL1- KO and interference altered the expression of most steroidogenic genes, including steroidogenic acute regulatory protein ( StAR ), cytochrome P450 family 11 subfamily A member 1( Cyp11a1 ), 3β-hydroxysteroid dehydrogenase 2 (Hsd3b2), 17-β-hydroxysteroid dehydrogenase 3 (Hsd17B3), cytochrome P450 family 17 subfamily A member 1( Cyp17a1 ), and cytochrome P450 aromatase (Cyp19a1). BMAL1- KO mice also altered the expression of related hormone receptor genes, including follicle-stimulating hormone receptor ( FSHr ), luteinizing hormone receptor ( LHr, Lhcgr ), and estrogen receptor β ( ERβ ) ( 15 , 20 – 23 , 41 , 77 , 94 , 95 ) ( Table 1 ). For example, BMAL1 knockdownin goat Leydig cells reduced testosterone production and the expression of StAR and HSD3B2, whereas BMAL1 overexpression enhanced testosterone production and the expression of StAR and Hsd17b2 ( 93 ).…”

Circadian Rhythms Within the Female HPG Axis: From Physiology to Etiology

“…Cyp19a1 itself also demonstrates a circadian rhythm. It was identified to peak at ZT16 during the dark period in a 12-hour light/12-hour dark cycle ( 52 ). Besides that, the circadian clock also participates in progesterone production, and steroid hormone–related enzyme (StAR) is a key enzyme in this process ( 8 ).…”