Close pathological correlations between chronic kidney disease and reproductive organ-associated abnormalities in female cotton rats
Authors: Ichii Osamu , Nakamura Teppei , Irie Takao , Kouguchi Hirokazu , Sotozaki Kozue , Horino Taro , Sunden Yuji , Elewa Yaser Hosny Ali , Kon Yasuhiro 
Published: February 2018

Cotton rat ( Sigmodon hispidus) is a useful experimental rodent for the study of human infectious diseases. We previously clarified that cotton rats, particularly females, developed chronic kidney disease characterized by cystic lesions, inflammation, and fibrosis. The present study investigated female-associated factors for chronic kidney disease development in cotton rats. Notably, female cotton rats developed separation of the pelvic symphysis and hypertrophy in the vaginal parts of the cervix with age, which strongly associated with pyometra. The development of pyometra closely associated with the deterioration of renal dysfunction or immunological abnormalities was indicated by blood urea nitrogen and serum creatinine or spleen weight and serum albumin/globulin ratio, respectively. These parameters for renal dysfunction and immunological abnormalities were statistically correlated. These phenotypes found in the female reproductive organs were completely inhibited by ovariectomy. Further, the female cotton rats with pyometra tended to show more severe chronic kidney disease phenotypes and immunological abnormalities than those without pyometra; these changes were inhibited in ovariectomized cotton rats. With regard to renal histopathology, cystic lesions, inflammation, and fibrosis were ameliorated by ovariectomy. Notably, the immunostaining intensity of estrogen receptor α and estrogen receptor β were weak in the healthy kidneys, but both estrogen receptors were strongly induced in the renal tubules showing cystic changes. In conclusion, the close correlations among female reproductive organ-associated abnormalities, immunological abnormalities, and renal dysfunction characterize the chronic kidney disease features of female cotton rats. Thus, the cotton rat is a unique rodent model to elucidate the pathological crosstalk between chronic kidney disease and sex-related factors. Impact statement The increasing number of elderly individuals in the overall population has led to a concomitant age-related increase in chronic kidney disease. Moreover, the global prevalence of patients with chronic kidney disease is gradually increasing, which poses a serious public health problem. The limited number of spontaneous chronic kidney disease animal models, which resemble chronic kidney disease pathogenesis in elderly individuals, is a major limitation in the development of experimental and curative medicines for chronic kidney disease. This pathological study clarified that sex-related factors, including hormones, and abnormalities of the female reproductive system, such as pyometra, are closely associated with chronic kidney disease development by using cotton rats ( Sigmodon hispidus). Further, ovariectomy inhibited the phenotypes of the female reproductive system, immunological abnormalities, and chronic kidney disease. Thus, this laboratory rodent serves as a novel and useful spontaneous chronic kidney disease model to elucidate the candidate disease factors and the pathogenesis of chronic kidney disease both in human and experimental medicine.