Characterization of mice deficient in melanocortin 2 receptor on a B6/Balbc mix background.

We have previously reported that Melanocortin 2 receptor (MC2R(-/-)) deficient mice on B6 N5 generations exhibited macroscopically detectable adrenal glands with markedly atrophied zona fasciculata (zF) and lack of detectable levels of corticosterone, and reduced serum concentrations of aldosterone and epinephrine. All MC2R(-/-) mice on B6/N8 background die within 2 days after birth, while about half of the MC2R(-/-) mice on B6/Balbc mix background survived to adulthood. Both male and female MC2R(-/-) mice were fertile, suggesting that normal development and function of reproductive organs. MC2R(-/-) mice delivered from MC2R(-/-) dams failed to survive due to lung failure, suggesting that fetal or maternal corticosterone is essential for lung maturation. MC2R(-/-) mice failed to activate the hypothalamic-pituitary-adrenal axis in response to both immune and non-immune stimuli. MC2R(-/-) mice maintained glomerular structure and achieved electrolyte homeostasis by the activation of the renin-angiotensin-aldosterone system under low aldosterone and undetectable levels of corticosterone.

Melanocortin 2 receptor is required for adrenal gland development, steroidogenesis, and neonatal gluconeogenesis.

ACTH (i.e., corticotropin) is the principal regulator of the hypothalamus-pituitary-adrenal axis and stimulates steroidogenesis in the adrenal gland via the specific cell-surface melanocortin 2 receptor (MC2R). Here, we generated mice with an inactivation mutation of the MC2R gene to elucidate the roles of MC2R in adrenal development, steroidogenesis, and carbohydrate metabolism. These mice, the last of the knockout (KO) mice to be generated for melanocortin family receptors, provide the opportunity to compare the phenotype of proopiomelanocortin KO mice with that of MC1R-MC5R KO mice. We found that the MC2R KO mutation led to neonatal lethality in three-quarters of the mice, possibly as a result of hypoglycemia. Those surviving to adulthood exhibited macroscopically detectable adrenal glands with markedly atrophied zona fasciculata, whereas the zona glomerulosa and the medulla remained fairly intact. Mutations of MC2R have been reported to be responsible for 25% of familial glucocorticoid deficiency (FGD) cases. Adult MC2R KO mice resembled FGD patients in several aspects, such as undetectable levels of corticosterone despite high levels of ACTH, unresponsiveness to ACTH, and hypoglycemia after prolonged (36 h) fasting. However, MC2R KO mice differ from patients with MC2R-null mutations in several aspects, such as low aldosterone levels and unaltered body length. These results indicate that MC2R is required for postnatal adrenal development and adrenal steroidogenesis and that MC2R KO mice provide a useful animal model by which to study FGD.

Cat-eye syndrome with isolated idiopathic hypogonadotropic hypogonadism.

A 34-year-old Japanese man diagnosed as having cat-eye syndrome (CES) with isolated idiopathic hypogonadotropic hypogonadism (IHH) was treated at our university. He showed preauricular pits/tags, downward slanting palpebral fissures, ocular hypertelorism, and strabismus. However, ocular coloboma and anal atresia, major characteristic features of CES, were negative. Chromosomal analysis revealed malformation in chromosome 22 and eunuchoid features and a low grade development of secondary sexual characteristics were also evident. Endocrinological examinations revealed that this patient was in a state of isolated IHH. Although CES with IHH is extremely rare, endocrine disorders should be given due attention.

Adult-onset idiopathic hypogonadotropic hypogonadism due to isolated pituitary gonadotropin deficiency.

A 25-year-old Japanese man with adult-onset idiopathic hypogonadotropic hypogonadism is reported. He had been delivered normally, had normal puberty, and experienced erectile dysfunction at age 24 years. Brain MRI revealed no abnormal findings and endocrinological data supported the diagnosis of isolated gonadotropin deficiency. Although most patients with idiopathic hypogonadotropic hypogonadism have a hypothalamic dysfunction, the lesion in this case may be considered to be in the pituitary since repetitive GnRH loading failed to increase serum LH and FSH.

Alternate promoter and 5'-untranslated exon usage of the mouse adrenocorticotropin receptor gene in adipose tissue.

Mouse adrenocorticotropin receptor (ACTH-R/MC2R) messenger ribonucleic acid (mRNA) is expressed predominantly in the adrenal gland and, to a lesser extent, in adipose tissue. In this study, we found a novel 135-bp exon 1 (exon 1f) of the ACTH-R gene transcribed in mouse adipose tissue by RNA ligase-mediated rapid amplification of cDNA ends, which was located 1.4 kb downstream in the genome of previously-reported exon 1 (exon 1a) transcribed in the adrenal gland. The novel promoter region, 1.4 kb upstream of exon 1f contained three CCAAT boxes. RT-PCR analysis revealed that ACTH-R mRNA from adipose tissue and differentiated 3T3-L1 adipocytes exclusively contained exon 1f. Thus, the promoter region flanking to exon 1f is thought to be essential for adipose tissue, while that flanking to exon 1a is specific for the adrenal gland. A search for a similar sequence of mouse ACTH-R exon 1f and its flanking region in the human genome sequence database of GenBank Human Genome Resources did not reveal such a sequence in the region of the human ACTH-R gene. This may explain the absence of ACTH-R expression in human adipose tissue.

Identification of a functional peroxisome proliferator-activated receptor responsive element within the murine perilipin gene.

Perilipin, a family of phosphoproteins located around lipid droplets in adipocytes, is essential for enlargement of lipid droplets and lipolytic reaction by hormone-sensitive lipase. Thiazolidinediones, peroxisome proliferator-activated receptor (PPAR) gamma agonists, have been shown to increase perilipin expression in fully differentiated adipocytes. However, the precise mechanism of transcriptional regulation of murine perilipin gene heretofore remains unclear. We determined the transcription start site of murine perilipin gene by RNA ligase-mediated rapid amplification of the cDNA ends method. We generated luciferase reporter gene constructs containing various lengths of the 5'-flanking region of the murine perilipin gene and assayed promoter/enhancer activities using differentiated 3T3-L1 adipocytes. We identified a functional PPAR-responsive element (PPRE) in the murine perilipin promoter, and this was confirmed by gel EMSAs using nuclear extracts from differentiated 3T3-L1 adipocytes. Furthermore, point mutations of the identified functional PPRE markedly reduced both the reporter gene activity in differentiated 3T3-L1 adipocytes and PPARgamma/thiazolidinedione-induced transactivation in NIH-3T3 fibroblasts. Real-time RT-PCR revealed that thiazolidinedione up-regulates endogenous perilipin mRNA levels. We propose that PPARgamma plays a significant role in the transcriptional regulation of murine perilipin gene via the PPRE in its promoter.