gms | German Medical Science

Objectives: Chronic psychosocial stress is a risk factor for the development of physical and mental disorders which are often accompanied by an over-reactive immune system. Given that chronic stress-induced immune activation is lacking in germ-free and antibiotics-treated mice, a causal role of the gut microbiome in the development of stress-related disorders is likely. We showed previously that chronic psychosocial stress disturbed bone homeostasis and endochondral ossification during long-bone growth. Here, we address the hypothesis that repeated fecal transplantation from non-stressed mice to stressed mice might attenuate the negative effects of stress on bone. Furthermore, we aimed to investigate the involvement of inflammatory markers in this process.

Methods: 7-weeks-old male C57BL/6N mice were subjected to the chronic subordinate colony housing (CSC) paradigm, a validated model for chronic psychosocial stress, for 19 days. CSC mice were housed in groups of four together with a dominant, significant heavier CD1 male mouse in order to induce chronic subordination. Single-housed (SHC) mice were used as controls. We repeatedly infused SHC and CSC recipient mice rectally with SHC donor feces at days 4 and 11 and assessed immunological and bone parameters on day 20 by plasma multiplex cytokine analysis and µCT analysis. Furthermore, SHC and CSC recipient mice were infused with CSC donor feces at respective days. To exclude effects of rectal infusions, another set of SHC and CSC mice was infused with saline. n=6-8/group. Mann-Whitney U/Kruskal-Wallis test with Bonferroni post-hoc analysis, p<0.05.

Results and conclusion: Keratinocyte chemoattractant (KC), interleukin (IL)-6 as well as monocyte chemoattractant protein (MCP)-1 levels were increased in the plasma of saline-infused CSC and CSC-recipient CSC vs. respective SHC animals, indicating increased immune activation by chronic stress. SHC-recipient CSC animals only showed increased MCP-1, but not KC and IL-6 levels when compared to their respective controls, indicating stress-protective effects of fecal transplantation from non-stressed mice. Regarding bone parameters, CSC mice displayed reduced tibia length, increased growth plate thickness, increased trabecular thickness and trabecular bone mineral density compared to control animals, indicating disturbed endochondoral ossification. The effects of stress on bone parameters were abolished when transplanting CSC mice with feces from non-stressed mice.

In conclusion, our data provide evidence for a role of the microbiome in adverse consequences of chronic psychosocial stress on bone. Transplantation of healthy feces might be a useful tool to attenuate the negative effects of chronic stress especially on bone growth. One mechanisms might be the reduced stress-induced immune activation under fecal transplantation treatment. This might be clinically relevant since children subjected to chronic psychosocial stress during childhood were shown to be of significant shorter stature.