Background: Circulating inflammatory markers increase with age. This pro-inflammatory milieu makes the organism less capable of coping with stressors such as stroke. Age related inflammation occurs in both the brain and peripheral tissues like the gastro-intestinal tract. There is increasing recognition that commensal bacteria in the GI tract are altered with age or with germ-free housing, affecting the brain. The change occurs most notably in the ratio of two major phyla of the microbiome, the Firmicutes and Bacteroidetes. Young age is associated with a low ratio of the two but this ratio increases with age, which has been linked to many diseases including obesity, hypertension, and diabetes which are major risk factors for stroke.
Hypothesis: We hypothesized that there would be age-related differences in the microbiome, and that restoration of a young microbiome would improve functional recovery in aged mice.
Methods: Fecal transplants from young and aged donors were administered to recipient animals after suppression of endogenous microbial compositions through concentrated Streptomycin. This allowed for successful colonization of the gut with the newly transplanted microbiome. A transient middle cerebral artery occlusion (MCAO) was used in young (3-4 month) and aged (18-20 month) male mice 4 weeks after transplant. Functional recovery was assessed by neurological deficit scores, the hang wire test, and open field activity. The Y-maze was used to assess cognitive impairment.
Results: We successfully reversed the microbiomes of aged organisms and gave young animals “aged” biomes. Animals with “aged” microbiomes prior to stroke had worsened functional recovery based on all behavioral tests. The “aged” biome increased mortality rates most notably in the young recipients which had over 50% mortality. Aged mice had significantly improved functional recovery as assessed by the HW test (P < 0.05) and NDS after reconstitution of “young” microbiome prior to stroke compared to aged control animals with the normal “aged” microbiomes.
Conclusion: Aged mice have high Firmicutes and Bacteroidetes relative abundances. Manipulation of the microbiome in young and aged mice is possible. Restoration of a youthful biome improved functional recovery in aged mice.