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WATER AND ELECTROLYTE HOMEOSTASIS

Progressive polyuria without vasopressin neuron loss in a mouse model for familial neurohypophysial diabetes insipidus

¹Department of Endocrinology and Diabetes, Field of Internal Medicine and ²Department of Functional Anatomy and Neuroscience, Nagoya University Graduate School of Medicine, Nagoya; ³Department of Metabolic Medicine, Nagoya University School of Medicine, Nagoya; ⁴Immuno-Biological Laboratories, Takasaki; and ⁵PhoenixBio, Utsunomiya, Japan

Submitted 20 January 2009 ; accepted in final form 11 March 2009

Familial neurohypophysial diabetes insipidus (FNDI), an autosomal dominant disorder, is mostly caused by mutations in the gene of neurophysin II (NPII), the carrier protein of arginine vasopressin (AVP). Previous studies suggest that loss of AVP neurons might be the cause of polyuria in FNDI. Here we analyzed knockin mice expressing mutant NPII that causes FNDI in humans. The heterozygous mice manifested progressive polyuria as do patients with FNDI. Immunohistochemical analyses revealed that inclusion bodies that were not immunostained with antibodies for mutant NPII, normal NPII, or AVP were present in the AVP cells in the supraoptic nucleus (SON), and that the size of inclusion bodies gradually increased in parallel with the increases in urine volume. Electron microscopic analyses showed that aggregates existed in the endoplasmic reticulum (ER) as well as in the nucleus of AVP neurons in 1-mo-old heterozygous mice. At 12 mo, dilated ER filled with aggregates occupied the cytoplasm of AVP cells, while few aggregates were found in the nucleus. Analyses with in situ hybridization revealed that expression of AVP mRNA was significantly decreased in the SON in the heterozygous mice compared with that in wild-type mice. Counting cells expressing AVP mRNA in the SON indicated that polyuria had progressed substantially in the absence of neuronal loss. These data suggest that cell death is not the primary cause of polyuria in FNDI, and that the aggregates accumulated in the ER might be involved in the dysfunction of AVP neurons that lead to the progressive polyuria.

hereditary disease; arginine vasopressin; endoplasmic reticulum; inclusion bodies