Mineralocorticoids induce polyuria by reducing apical aquaporin-2 expression of the kidney in partial vasopressin deficiency.

The symptoms of diabetes insipidus may be masked by the concurrence of adrenal insufficiency and emerge after the administration of hydrocortisone, occasionally at high doses. To elucidate the mechanism underlying polyuria induced by the administration of high-dose corticosteroids in the deficiency of arginine vasopressin (AVP), we first examined the secretion of AVP in three patients in whom polyuria was observed only after the administration of high-dose corticosteroids. Next, we examined the effects of dexamethasone or aldosterone on water balance in wild-type and familial neurohypophyseal diabetes insipidus (FNDI) model mice. A hypertonic saline test showed that AVP secretion was partially impaired in all patients. In one patient, there were no apparent changes in AVP secretion before and after the administration of high-dose corticosteroids. In FNDI mice, unlike dexamethasone, the administration of aldosterone increased urine volumes and decreased urine osmolality. Immunohistochemical analyses showed that, after the administration of aldosterone in FNDI mice, aquaporin-2 expression was decreased in the apical membrane and increased in the basolateral membrane in the collecting duct. These changes were not observed in wild-type mice. The present data suggest that treatment with mineralocorticoids induces polyuria by reducing aquaporin-2 expression in the apical membrane of the kidney in partial AVP deficiency.

Deficiency of WFS1 leads to the impairment of AVP secretion under dehydration in male mice.

Wolfram syndrome (WS) is mainly caused by mutations in the WFS1 gene and characterized by diabetes mellitus, optic atrophy, hearing loss, and central diabetes insipidus (CDI). WFS1 is an endoplasmic reticulum (ER)-resident transmembrane protein, and Wfs1 knockout (Wfs1-/-) mice, which have been used as a mouse model for WS, reportedly manifested impairment of glucose tolerance due to pancreatic ß-cell loss. In the present study, we examined water balance, arginine vasopressin (AVP) secretion, and ER stress in AVP neurons of the hypothalamus in Wfs1-/- mice. There were no differences in urine volumes between Wfs1-/- and wild-type mice with free access to water. Conversely, when mice were subjected to intermittent water deprivation (WD) for 20 weeks, during which water was unavailable for 2 days a week, urine volumes were larger in Wfs1-/- mice, accompanied by lower urine AVP concentrations and urine osmolality, compared to wild-type mice. The mRNA expression of immunoglobulin heavy chain binding protein, a marker of ER stress, was significantly increased in the supraoptic nucleus and paraventricular nuclei in Wfs1-/- mice compared to wild-type mice after WD. Our results thus showed that Wfs1 knockout leads to a decrease in AVP secretion during dehydration, which could explain in part the mechanisms by which Wfs1 mutations cause CDI in humans.

Arginine vasopressin-Venus reporter mice as a tool for studying magnocellular arginine vasopressin neurons.

Arginine vasopressin (AVP) synthesized in the magnocellular neurons of the hypothalamus is transported through their axons and released from the posterior pituitary into the systemic circulation to act as an antidiuretic hormone. AVP synthesis and release are precisely regulated by changes in plasma osmolality. Magnocellular AVP neurons receive innervation from osmosensory and sodium-sensing neurons, but previous studies showed that AVP neurons per se are osmosensitive as well. In the current study, we made AVP-Venus reporter mice and showed that Venus was expressed exclusively in AVP neurons and was upregulated under water deprivation. In hypothalamic organotypic cultures from the AVP-Venus mice, Venus-labeled AVP neurons in the supraoptic and paraventricular nuclei survived for 1 month, and Venus expression was upregulated by forskolin. Furthermore, in dissociated Venus-labeled magnocellular neurons, treatment with NaCl, but not with mannitol, decreased Venus fluorescence in the soma of the AVP neurons. Thus, Venus expression in AVP-Venus transgenic mice, as well as in primary cultures, faithfully showed the properties of intrinsic AVP expression. These findings indicate that AVP-Venus mice as well as the primary hypothalamic cultures could be useful for studying magnocellular AVP neurons.

Critical amino acid variants in HLA-DRB1 allotypes in the development of Graves' disease and Hashimoto's thyroiditis in the Japanese population.

The effects of amino acid variants encoded by human leukocyte antigen (HLA) class II on the development of Graves' disease (GD) and Hashimoto's thyroiditis (HT) have not been fully elucidated. We investigated the HLA-DRB1 genes of 243 GD patients and 82 HT patients in the Japanese population and compared the frequencies of HLA-DRB1 alleles and HLA-DRB1 amino acid variants between these patients and the Japanese populations previously reported by another institution. The frequencies of HLA-DRB1*04:05 and -DRB1*14:03 alleles were significantly higher and those of HLA-DRB1*01:01 and -DRB1*15:02 alleles were lower in GD patients than in controls. The frequencies of HLA-DRB1*08:03 and -DRB1*09:01 alleles were significantly higher and that of the HLA-DRB1*13:02 allele was lower in HT patients than in controls. A blind association analysis with all amino acid positions identified DRß9 and DRß31 for GD and DRß9, DRß13, and DRß21 for HT. The frequency of Glu-9 was significantly higher and that of Cys-9 was lower in GD patients than in controls. The frequencies of Lys-9 and Phe-13 were significantly higher in HT patients than in controls. DRß9 and DRß13 could be critical amino acid positions in the development of GD and HT.

Endoplasmic reticulum chaperone BiP/GRP78 knockdown leads to autophagy and cell death of arginine vasopressin neurons in mice.

The immunoglobulin heavy chain binding protein (BiP), also referred to as 78-kDa glucose-regulated protein (GRP78), is a pivotal endoplasmic reticulum (ER) chaperone which modulates the unfolded protein response under ER stress. Our previous studies showed that BiP is expressed in arginine vasopressin (AVP) neurons under non-stress conditions and that BiP expression is upregulated in proportion to the increased AVP expression under dehydration. To clarify the role of BiP in AVP neurons, we used a viral approach in combination with shRNA interference for BiP knockdown in mouse AVP neurons. Injection of a recombinant adeno-associated virus equipped with a mouse AVP promoter and BiP shRNA cassette provided specific BiP knockdown in AVP neurons of the supraoptic (SON) and paraventricular nuclei (PVN) in mice. AVP neuron-specific BiP knockdown led to ER stress and AVP neuronal loss in the SON and PVN, resulting in increased urine volume due to lack of AVP secretion. Immunoelectron microscopy of AVP neurons revealed that autophagy was activated through the process of AVP neuronal loss, whereas no obvious features characteristic of apoptosis were observed. Pharmacological inhibition of autophagy by chloroquine exacerbated the AVP neuronal loss due to BiP knockdown, indicating a protective role of autophagy in AVP neurons under ER stress. In summary, our results demonstrate that BiP is essential for the AVP neuron system.

Degradation of Mutant Protein Aggregates within the Endoplasmic Reticulum of Vasopressin Neurons.

Misfolded or unfolded proteins in the ER are said to be degraded only after translocation or isolation from the ER. Here, we describe a mechanism by which mutant proteins are degraded within the ER. Aggregates of mutant arginine vasopressin (AVP) precursor were confined to ER-associated compartments (ERACs) connected to the ER in AVP neurons of a mouse model of familial neurohypophysial diabetes insipidus. The ERACs were enclosed by membranes, an ER chaperone and marker protein of phagophores and autophagosomes were expressed around the aggregates, and lysosomes fused with the ERACs. Moreover, lysosome-related molecules were present within the ERACs, and aggregate degradation within the ERACs was dependent on autophagic-lysosomal activity. Thus, we demonstrate that protein aggregates can be degraded by autophagic-lysosomal machinery within specialized compartments of the ER.