Stohn, J. P. | bioRxiv Science

bioRxiv2026

Short- and Long-Term Effects of Social Isolation on Adult Murine Bone are Sex-Dependent

Social isolation is a known modifiable risk factor for many chronic diseases including cardiovascular, metabolic, and neurological disorders. Recent research has demonstrated that social isolation is similarly detrimental to skeletal health, but these effects may be sexually dimorphic. In rodents, isolation negatively affects bone in adult male mice, but not in females. However, these sex differences have not been systematically investigated, and it is unknown if they persist with long-term social isolation. The goal of our study was to investigate if isolation-induced bone loss may occur on different timescales between female and male mice, as well as investigate the potential roles of estrogen and testosterone. We examined bone changes in grouped (4 mice/cage) or isolated (1 mouse/cage) female and male 16-week-old C57BL/6J mice after 2, 4, or 8 weeks of treatment. We found that social isolation through single housing significantly reduced bone parameters across treatment lengths in male mice (20% average reduction in Tb.BV/TV; 8% average reduction in Ct.Th.) but not in females even with prolonged isolation. In trabecular bone, isolation affected male bone parameters in as little as 2 weeks. Isolation also decreased biomechanical properties in the femur of male but not female mice. While the females overall bone phenotype was unaffected, isolated females did show an increase in bone turnover markers with 2 weeks of isolation. Isolation also altered estrogen-related gene expression in male mice isolated for 4 or 8 weeks. Overall, our results demonstrate that both short- and long-term social isolation has sexually dimorphic effects on murine bone. These findings have important clinical implications for individuals at risk for social isolation, as well as for pre-clinical rodent models utilizing single housing. Lay SummarySocial isolation may have worse effects on bone in males than females, but this has not been thoroughly explored. We investigated if different lengths of isolation had different effects on the bones of male and female mice. We found that both short- and long-term isolation had a rapid and negative impact on the bones of male but not female mice, although isolated females did show some changes in markers of bone formation and resorption. These findings have important implications for humans at risk for social isolation, as well as for studies with rodents that use single housing.

physiology↗

bioRxiv2024

Thermoneutral Housing has Limited Effects on Social Isolation-Induced Bone Loss in Male C57BL/6J Mice

Social isolation stress has numerous known negative health effects, including increased risk for cardiovascular disease, dementia, as well as overall mortality. The impacts of social isolation on skeletal health, however, have not been thoroughly investigated. We previously found that four weeks of social isolation through single housing led to a significant reduction in trabecular and cortical bone in male, but not female, mice. One possible explanation for these changes in male mice is thermal stress due to sub-thermoneutral housing. Single housing at room temperature ([~]20-25{degrees}C)--below the thermoneutral range of mice ([~]26-34{degrees}C)--may lead to cold stress, which has known negative effects on bone. Therefore, the aim of this study was to test the hypothesis that housing mice near thermoneutrality, thereby ameliorating cold-stress, will prevent social isolation-induced bone loss in male C57BL/6J mice. 16-week-old mice were randomized into social isolation (1 mouse/cage) or grouped housing (4 mice/cage) at either room temperature ([~]23{degrees}C) or in a warm temperature incubator ([~]28{degrees}C) for four weeks (N=8/group). As seen in our previous studies, isolated mice at room temperature had significantly reduced bone parameters, including femoral bone volume fraction (BV/TV), bone mineral density (BMD), and cortical thickness. Contrary to our hypothesis, these negative effects on bone were not ameliorated by thermoneutral housing. Social isolation increased glucocorticoid-related gene expression in bone and Ucp1 and Pdk4 expression in BAT across temperatures, while thermoneutral housing increased percent lipid area and decreased Ucp1 and Pdk4 expression in BAT across housing conditions. Overall, our data suggest social isolation-induced bone loss is not a result of thermal stress from single housing and provides a key insight into the mechanism mediating the effects of isolation on skeletal health. Lay SummarySocial isolation is a major public health concern and is known to increase the risk for many diseases, including heart disease and dementia. The impact of social isolation on bone health, however, has not been well-studied. We previously found that four weeks of social isolation reduces bone in male mice. Isolated mice may experience more cold stress than mice housed in groups, as we commonly keep laboratory mice at temperatures below their ideal range, which could lead to bone loss. The aim of our study was therefore to test if housing mice at warmer temperatures, within their ideal temperature range, prevents isolation-induced bone loss in male mice. We found that housing mice at warmer temperatures did not fully prevent isolation-induced bone loss. We also found social isolation increased the expression of genes related to glucocorticoid signaling in bone across temperatures, as well as genes associated with mitochondrial metabolism within fat tissue. Overall, our results show that social isolation-induced bone loss is likely not a result of cold stress from single housing and provide insight into the mechanisms by which isolation causes bone loss.

physiology↗