Alamandine/MrgD Pathway Modulates Gut-Bone Marrow Axis in Aging

Aging is associated with colon epithelial barrier integrity and upregulation of myelopoiesis in the bone marrow (BM). Alamandine (Ala) and MrgD are novel members of the renin angiotensin system (RAS). This study tested the hypothesis that Ala restores the colon epithelial barrier integrity in aging via modulating gut-BM axis. Mice of age 2-3 (Young) or 22-24 months (Old) were treated with saline or Ala by using Osmotic pumps. The intestinal permeability was evaluated by using FITC-dextran. Lgr5⁺Olfm4⁺ intestinal stem cells (ISCs), Wnt3a and β-catenin were evaluated by immunohistochemistry or western blotting. Fecal microbiome was analyzed by 16S rRNA sequencing. Monocyte-macrophages were characterized by flow cytometry. Cecal or serum bacterial metabolites were analyzed. The pro-myelopoietic potential of cecal supernatants (CS) was tested in the Young-BM cells. MrgD was expressed in ISCs, which was decreased in the Old. Increased intestinal permeability in aging was reversed by Ala. In the colon organoids, Ala increased Wnt3a levels that were antagonized by the NF449, SQ22536 or 666-15. Ala restored phospho-CREB and active β-catenin levels that were decreased in the Old colon-organoids. Ala increased the richness and β-diversity of the aging microbiome and decreased <i>Bacillota</i>/<i>Bacteroidota</i>. Ala decreased the CD80⁺ and increased CX3CR⁺ cells in the Old colons. Old-CS induced myelopoiesis in vitro in BM cells with higher number of monocytes and pro-inflammatory macrophages which was not observed in the CS derived from Ala-treated Old mice. Ala is a promising pharmacological agent for reversing the leaky gut of aging by restoring homeostasis in the gut-BM axis.