Role Of LRH-1 Research Articles

Abstract 281: Hepatic Liver Receptor Homolog-1, a Key Regulator of Lipid Storage and Phospholipid Diversity

Cardiovascular disease and malignancy are the most common cause of death in Non-alcoholic Steatohepatitis (NASH) patients. Aside from lifestyle modification, there is currently no treatment for NASH. Activation of Liver Receptor Homolog-1 (Lrh-1), known to bind phospholipid ligands, has been shown to effectively reduce liver triglyceride (TG) in DIO mice, raising Lrh-1 as a possible target for treating NASH. Despite this finding, hepatic TGs are equivalent in controls and liver-specific Lrh-1 knockout (LKO or Lrh1 AlbCre ) mice, regardless of diet. Given this discrepancy, we sought to characterize Lrh-1’s role in hepatic lipid metabolism by acutely deleting Lrh-1 in the adult liver, thus eliminating potential compensatory developmental effects associated with LKO. To acutely eliminate Lrh-1 in hepatocytes, 6-week old Lrh-1 fl/f l male mice were infected with AVV8-TBG-eGFP (Control) or AAV8-TBG-Cre (LKO AAVCre ) via retro-orbital injection and fed chow or high fat diet. LKO AAVCre mice developed hepatic steatosis after six weeks on standard chow or high fat diet. Furthermore, LKO AAVCre hepatocytes exhibited large lipid droplets, which were visible as early as 2 wks post-infection, thus suggesting that lipid handling is significantly altered in LKO AAVCre hepatocytes, independent of fatty acid transport or oxidation. LKO AAVCre exhibited lower Pcsk9 expression, which correlated with decreased fasting plasma LDL-C. Consistent with other studies showing that perturbations in phospholipid pools affect lipid storage, lipidomic analyses revealed a significant reduction in phospholipid species containing arachidonic acid (AA), thus reducing the overall diversity of key membrane phospholipids. RNA-Seq analyses from LKO AAVCre livers confirmed that factors promoting lipid droplet size ( Cidec , Plin4 ) were greatly increased while key enzymes in biosynthesis of unsaturated fatty acids were reduced ( Fads1, Fads2 and Elovl5 ). In addition, expression of human LRH-1 in LKO AAVCre decreased hepatic TG and improved glucose tolerance in DIO mice, in a ligand dependent manner. Collectively our data establish a novel role for Lrh-1 as a key regulator of lipid storage, thereby providing the first in vivo evidence as to why phospholipid serve as Lrh-1 ligands.

Editorial: Molecular Endocrinology Articles in the Spotlight for April 2012

We are pleased to feature the following articles in this month’s issue of Molecular Endocrinology. Interestingly, the 3 articles provide novel insights into various hypothalamic pathways that regulate important aspects of reproduction and metabolism. In “GnRH Pulse Frequency-Dependent Stimulation of FSH Transcription Is Mediated via Activation of PKA and CREB,” Thompson et al provide a mechanism of GnRH pulse frequency-dependent activation of FSH involving differential activation of protein kinase A (PKA) and subsequent differential levels of cAMP-responsive element-binding protein (CREB) phosphorylation. LH gene expression is unaffected by this pathway. Furthermore, GnRH preferentially stimulates CREB phosphorylation at slow pulse frequencies, whereas PKA (the main regulator of CREB phosphorylation in the murine LT2 gonadotrope cell model) activity increases to a greater extent at slow GnRH pulse frequencies, correlating with the increase in CREB phosphorylation. Because pulsatile GnRHregulatestheexpressionandsecretionofbothFSH and LH, this work identifies the intracellular mechanism downstream of GnRH receptor activation responsible for triggering the diverse reproductive consequences of the individual gonadotropins. “Nuclear Receptor LRH-1 Induces the Reproductive Neuropeptide Kisspeptin in the Hypothalamus” by Atkin et al (freely available at http://mend.endojournals.org/) provides novel insights into the molecular mechanism controlling kisspeptin’s differential secretion. The authors show that mice lacking LRH-1 in kisspeptin neurons have reduced plasma FSH levels and corresponding defects in follicle maturation and ovulation in the ovary. These knockout mice have a prolonged estrous cycle and deliver fewer pups per litter. On a molecular level, these findings help explain why kisspeptin is differentially regulatedindistinctregionsofthehypothalamus,thearcuate and anteroventral periventricular nuclei, and have revealed an important role for LRH-1 in regulating the female reproductive axis. Groba et al’s “Hypothyroidism Compromises Hypothalamic Leptin Signaling in Mice” reveals that leptin signaling in hypothalamic arcuate neurons is compromised under hypothyroid conditions. Activation of the Janus kinase (JAK)-signal transducer and activator of transcription (STAT) pathways by leptin is reduced in hypothyroid obese (ie, ob/ob) mice as evidenced by reduced phopho-STAT3 immunoreactivity and decreased SOCS3 expression. A diminished reduction in body weight and food intake in hypothyroid ob/ob mice was observed after leptin treatment. Importantly, hypothyroidism is associated with elevated transcript levels of shorter leptin receptor isoforms. Consequently, up-regulation of the shorter isoforms of the leptin receptor may represent a major mechanism by which hypothyroidism influences the leptin signaling pathway in hypothyroid mice.

Human CD34+ Myeloid Leukemic Progenitor Cells Are Susceptible to Lysis by Minor Histocompatibility Antigen LRH-1-Specific Cytotoxic T Lymphocytes.

Allogeneic stem cell transplantation (SCT) is a specialized form of immunotherapy for treating patients with hematological malignancies. The curative potential is attributed to the graft-versus-tumor (GVT) response during which donor-derived cytotoxic T lymphocytes (CTL) eliminate malignant cells of the recipient. Minor histocompatibility antigens (MiHA) are the major targets of the GVT response, and expansion of MiHA-specific CTL has been shown to coincide with tumor remission following SCT. Recently, we identified a novel hematopoietic cell-restricted MiHA, designated LRH-1, which is presented by HLA-B7 and encoded by the P2X5 purinergic receptor gene (J. Clin. Invest. 2005: 115:3506–3516). Interestingly, tetramer analysis showed a direct association between in vivo expansion of LRH-1-specific CD8+ T cells and the disappearance of Bcr-Abl positive tumor cells in the CML patient from whom LRH-1-specific CTL was originally isolated. In addition, we detected in vivo expansion of LRH-1-specific CTL in an AML patient who was in clinical remission without GVHD. Furthermore, we demonstrated that P2X5 mRNA is significantly expressed in leukemic CD34+ progenitor cells from most CML as well as AML patients. These findings indicate a role for LRH-1 in inducing GVT immunity against myeloid leukemic progenitor cells. Here, we investigated the ex vivo responsiveness of myeloid leukemic CD34+ progenitor cells to LRH-1-specific CTL. First, we addressed this question using the CD34+ KG1 cell line which is positive for LRH-1. By using a CFSE-based survival assay we demonstrated that KG1 cells stably transfected with HLA-B7 could be efficiently lysed by LRH-1-specific CTL. Next, we determined responsiveness of purified CD34+ progenitor cells from HLA-B7+ CML patients to LRH-1 CTL-mediated killing. In the CFSE-based survival assay as well as a hematopoietic progenitor cell inhibition assay we showed that LRH-1-specific CTL efficiently recognize and kill CD34+ progenitor cells from LRH-1+ CML patients. In contrast, LRH-1-specific CTL did not inhibit the proliferation of CD34+ progenitor cells from LRH-1- CML patients. These findings illustrate that the P2X5-encoded LRH-1 antigen is an attractive target for adequate eradication of myeloid leukemic progenitor cells after allogeneic SCT.

The nuclear receptor LRH-1 critically regulates extra-adrenal glucocorticoid synthesis in the intestine

The nuclear receptor liver receptor homologue-1 (LRH-1, NR5A2) is a crucial transcriptional regulator of many metabolic pathways. In addition, LRH-1 is expressed in intestinal crypt cells where it regulates the epithelial cell renewal and contributes to tumorigenesis through the induction of cell cycle proteins. We have recently identified the intestinal epithelium as an important extra-adrenal source of immunoregulatory glucocorticoids. We show here that LRH-1 promotes the expression of the steroidogenic enzymes and the synthesis of corticosterone in murine intestinal epithelial cells in vitro. Interestingly, LRH-1 is also essential for intestinal glucocorticoid synthesis in vivo, as LRH-1 haplo-insufficiency strongly reduces the intestinal expression of steroidogenic enzymes and glucocorticoid synthesis upon immunological stress. These results demonstrate for the first time a novel role for LRH-1 in the regulation of intestinal glucocorticoid synthesis and propose LRH-1 as an important regulator of intestinal tissue integrity and immune homeostasis.

Estrogen—the Good, the Bad, and the Unexpected

I. IntroductionII. The Concept of Local Estrogen BiosynthesisIII. Aromatase and Its GeneIV. The ArKO MouseV. The ArKO Mouse and the Metabolic SyndromeVI. The Metabolic Syndrome in Humans with Natural Mu-tations in AromataseVII. Summary of the Metabolic Effects of EstrogensVIII. Local Aromatase Expression in the Breast and BreastCancerIX. Role of LRH-1 in Aromatase Expression in the Breast

Liver receptor homologue-1 is expressed in the adrenal and can regulate transcription of 11 beta-hydroxylase.

Liver receptor homologue-1 (LRH-1, designated NR5A2) is a mammalian homologue of Drosophila fushi tarazu factor (dFTZ-F1) and structurally belongs to the orphan nuclear receptor superfamily. LRH-1 can recognize the DNA sequence 5'-AAGGTCA-3', the canonical recognition motif for steroidogenic factor 1 (SF-1). Herein, we hypothesized that LRH-1 might play a role in the regulation of human adrenal expression of steroidogenic enzymes. To test this hypothesis, LRH-1 expression in human adult and fetal adrenal glands was examined by RT-PCR analysis. The fetal and adult adrenal glands, as well as liver and pancreas, were observed to express LRH-1 mRNA using RT-PCR. The ability of LRH-1 to enhance transcription of the gene encoding human 11 beta- hydroxylase (hCYP11B1) was then examined using the H295R adrenal cell line. LRH-1 co-transfection with hCYP11B1 luciferase promoter constructs caused a 25-fold induction of luciferase activity. Furthermore, co-transfection of a hCYP11B1 reporter construct containing a mutation in the SF-1 binding cis-element abolished the stimulatory effect of both SF-1 and LRH-1. Electrophoretic mobility shift assay (EMSA) demonstrated that LRH-1 could bind to the SF-1 response element. Taken together, our data suggested that LRH-1 is expressed in the adrenal, and can substitute for SF-1 to enhance transcription of genes encoding certain of the steroid-metabolizing enzymes. A role for LRH-1 in the regulation of adrenal or gonadal steroid hormone production should be further studied.