Mitsumasa Kubo

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.

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.

Genomic organization of the mouse adrenocorticotropin receptor

As a step for analysis of the transcriptional regulation of the adrenocorticotropin (ACTH) receptor gene, I have made an attempt to obtain a full length cDNA and determined the genomic organization of the mouse ACTH receptor. Using the 5-RACE (rapid amplification of cDNA ends) method, a 374bp sequence upstream of the translation start codon ATG of the receptor was obtained. By comparison of the 374bp sequence with the 1.8kb genomic sequence within the phage clone, lambda mCTR8, containing the mouse ACTH receptor coding region as described previously, a 95bp sequence of the 5-RACE-generated cDNA was found to locate from the position of -1 to -95 from the ATG, and a 113bp sequence of the 5-RACE-generated cDNA was found in the genomic sequence approximately 1.6kb upstream of the ATG. Because of the absence of a 166bp sequence, -209 to -374, in lambda mCTR8, further screening of a mouse genomic library was performed. By analysis of two positive clones, a 109bp and a 57bp sequence, -266 to -374 and -209 to -265, respectively, were located approximately 6.0kb away from each other in the phage clones which were not overlapped with lambda mCTR8. The 3non-coding region of the mouse ACTH receptor cDNA obtained by 3-RACE method was contiguous to the coding region by comparing it with the 1.4kb genomic sequence downstream of the ATG. The polyadenylation signal AATAAA was located at the position of 1291 from the ATG. Taken together, the mouse ACTH receptor gene consists of at least 4 exons and three of the exons encoded 5-untranslated sequences. Moreover, two mRNAs in the presence and absence of the 57bp putative exon 2 generated by alternative splicing were determined by reverse transcription/polymerase chain reaction between putative exon 1 and 4. Finally, the longest cDNA of this gene determined from this experiment was 1707bp while northern analysis revealed approximately 1.8kb mRNA in mouse adrenal gland. It awaits further investigation to clarify the significance of 5-untranslated non-coding exons and alternative splicing in this receptor gene.

Giant cell granulamatous hypophysitis with remarkable uptake on Gallium‐67 scintigraphy

We treated a man with giant cell granulomatous hypophysitis with pituitary enlargement, as seen on magnetic resonance imaging. Endocrinological examination revealed panhypopituitarism and diabetes insipidus. Microscopic examination of the specimen obtained by transsphenoidal pituitary biopsy revealed a granulomatous lesion, composed of epitheliod cells, Langhans multinucleated giant cells, lymphocytes and other chronic inflammatory cells. On whole body gallium‐67 scintigraphy, there was extensive uptake in the pituitary gland. Gallium‐67 scintigraphy may greatly aid in the diagnosis of granulomatous hypophysitis.

A rare case of acromegaly associated with pachydermoperiostosis

Pachydermoperiostosis (PDP) is a rare syndrome manifested clinically by finger clubbing, extremity enlargement, hypertrophic skin changes, and periosteal bone formation. The pathogenesis of the disorder has not been clarified and few endocrine abnormalities were apparent. We report here a 58-year-old man with acromegaly associated with PDP, the features of clubbed fingers, coarse skin, and cutis verticis gyrata. Acromegaly due to GH-producing pituitary adenoma was confirmed in endocrinological and pathological studies.

A rare case of Gitelman’s syndrome presenting with hypocalcemia and osteopenia

Gitelman’s syndrome (GS), an autosomal recessive disorder caused by a defect of the thiazide-sensitive NaCl cotransporter (TSC) at the distal tubule, is characterized by hyperreninemic hyperaldosteronism with normal or low blood pressure, hypokalemia, metabolic alkalosis, hypomagnesemia and hypocalciuria. An 18-yr-old Japanese man was admitted to our hospital with a history of muscle weakness and transient tetanic episodes. He showed hypocalcemia in addition to hypokalemia, severe hypomagnesemia, hypocalciuria and hyperreninemic hyperaldosteronism with normal blood pressure. Furthermore, bone mineral density at the lumbar spine revealed osteopenia. A diagnosis of GS was made on the basis of clinical features, laboratory data and renal function test. The electrolyte imbalance was corrected and bone mineral density was slightly increased with chronic treatment of magnesium and potassium salts. Genetic analysis revealed that TSC gene of the patient has a heterozygous C to A nucleotide substitution at position 545 in exon 4, which causes a threonine (Thr) to lysine (Lys) substitution at position 180. This is a rare case of GS with hypocalcemia and osteopenia which could be caused by severe hypomagnesemia.

A case of reversed pituitary dysfunction with intrasellar mass

Hypopituitarism can be caused by tumor, inflammation, granuloma and injuries. Once pituitary function is disturbed, hormone replacement therapy is necessary for the remaining life span in most cases. We have experienced a rare case of a unique intrasellar mass associated with pituitary dysfunction in which both spontaneously reversed. A 61-yr-old woman developed hypoadrenalism and central diabetes insipidus (cDI). Magnetic resonance (MR) imaging revealed a lobular, strong hypointense lesion with spotty signal in the middle of the hypophysis. This spotty lesion showed isointensity on T1- and high-intensity on T2-weighted MR images. The spotty signal as well as the normal pituitary lobe were enhanced by the administration of gadolinium. As replacement therapies for hypoadrenalism and cDI, 10 mg of hydrocortisone and 2.5 μg of desmopressin acetate were prescribed. Three months later, slight shrinkage of intrasellar mass and spontaneous improvement of pituitary functions were found. Hydrocortisone was then discontinued. Furthermore, because polyuria and polydipsia were improved nine months later, desmopressin acetate was stopped. Currently, the intrasellar mass continues to shrink, and the patient shows no symptoms without medication. Based upon the unique features of MR images, we suspect that the origin of the mass is an intrasellar hemangioma.