Negative impact of single housing on chronic kidney disease mineral and bone disorder outcomes

Chronic kidney disease (CKD) is a disorder of acquired disrupted mineral metabolism that affects millions in the United States and has no cure. Due to disturbed mineral homeostasis bones are particularly affected showing substantial bone loss during CKD and intricately linked with morbidity and mortality. Animal models serve as a crucial platform to investigate and elucidate the tissue cross-communication that facilitates pathogenic changes during CKD. One preclinical rodent model gaining in popularity is the adenine-diet induced CKD, which negates the requirement for highly technical surgical interventions and displays several of the CKD disrupted mineral metabolism hallmarks observed in patients. Interestingly, although CKD alone can negatively impact bone, other factors, such as individual housing, can impair normal bone homeostasis. This could be encountered experimentally especially when generating experimental animals in-house, in particular, using males that maintain aggressive territorial actions. We sought to evaluate the impact of reduced cage housing numbers, replicating potentially encountered cage number conditions, on the progression of CKD. We hypothesized that single housing alone would accelerate bone loss and therefore exacerbate CKD mineral dysregulation and related outcomes. To test this, C57BL/6J male mice at 10 wk old were maintained at 5-, 3-, or 1-mice per cage while receiving casein-control or the CKD-inducing adenine diet. We found that within 4 wk of diet administration, individually housed mice had more profound weight loss corresponding with increased circulating urea, hyperphosphatemia, and bone loss compared to mice maintained at 5 per cage. Additionally, 50% of the individually housed CKD animals developed cardiovascular calcifications, a sequelae of impaired mineral excretion. These data demonstrate housing density significantly impacts outcomes related to CKD and an important variable to consider when conducting basic and translational mouse CKD studies.