#4127 modulation of blood pressure through microbiome exchange between milan normotensive and hypertensive strains of rats

Abstract Background and Aims Hypertension is one of the major health problems contributing to the development of cardiovascular diseases. In contrast to essential hypertension, which often displays complex pathogenesis due to multifactorial aetiology, several monogenic forms of hypertension are caused by mutations in genes associated with renal salt handling. Thus, studies on monogenic forms of hypertension could hold potential for novel therapeutic approaches for essential hypertension. Recently, increasing numbers of studies have demonstrated the alteration of the gut microbiome in pathological states including hypertension. These observations suggest the involvement of the intestinal microbiome in the development and/or maintenance of hypertension. A reciprocal congenic strain of Milan hypertensive rat (NA rat), harbouring a missense mutation in the gene encoding the alpha subunit of the membrane-skeletal protein adducin (Add1), develops hypertension starting from 3 months after birth. Preliminary studies on NA rats and its littermate Milan normotensive (MN) rats showed diverse expression patterns of renal sodium transporters/ion channels in two strains of rats, indicating a putative role of altered renal salt handling on the enhanced blood pressure in NA rats (unpublished data). Based on this background, the aim of this study was to investigate a possible connection between the gut microbiome and blood pressure phenotypes in these two strains. Furthermore, we evaluated whether the exchange of faeces between the two strains could transfer the phenotypes through the gut microbiome. Finally, mechanisms underlying the altered phenotype after microbiome exchange were investigated. Method Hypertensive NA rats and normotensive MN rats were subjected to ‘homogenization (HOM)’ of the microbiome after birth, which consisted of the exchange of bedding containing faeces from either strain, followed by co-housing of MN and NA rats in the same cage (MN-HOM and NA-HOM groups). For the baseline (BSL) condition, rats were homogenized within the same strain (MN-BSL and NA-BSL). At the age of 5 months, blood pressure measurement was performed using a non-invasive tail-cuff BP-2000 Blood Pressure Analysis system. Faeces from each rat were collected for microbiota metataxonomic analysis using next generation sequencing of 16S ribosome encoding DNA. At the end of the treatment, rats were sacrificed for the collections of blood and organs to assess the expressions of genes involved in renal salt reabsorption. Results Systolic blood pressure (SBP) in MN-BSL was averaged at 143.6 mmHg, while NA-BSL showed average SBP 163.3 mmHg, confirming the hypertensive phenotype in NA rats at baseline (P<0.001). Interestingly, MN-HOM showed a significantly enhanced SBP compared to MN-BSL, reaching 153.5 mmHg (P = 0.005). On the other hand, the average SBP of NA-HOM was163.7 mmHg, indicating that homogenization did not significantly impact blood pressure in NA rats. Although the MN-HOM group showed significantly increased SBP compared with MN-BSL group, the average SBP of MN-HOM was still significantly lower than both the NA-BSL and NA-HOM groups. Different gut microbiota compositions were observed in the two strains of rats at baseline, and HOM altered both. Conclusion We have demonstrated that the hypertensive phenotype in NA rats was transferred to normotensive MN rats through the exchange of gut microbiota, indicating that the intestinal microbiota and/or metabolites derived therefrom could eventually modulate blood pressure. Further studies including immunoblotting as well as uremic toxin analyses are required to unveil the molecular mechanisms by which the gut microbiome modulates blood pressure.