Bonin, J. L. | bioRxiv Science

bioRxiv2023

The Resolvin D2-GPR18 Axis Enhances Bone Marrow Function and Limits Hepatic Fibrosis in Aging

Aging is associated with non-resolving inflammation and tissue dysfunction. Resolvin D2 (RvD2) is a pro-resolving ligand that acts through the G-protein coupled receptor (GPCR) called GRP18. Using an unbiased screen, we report increased Gpr18 expression in macrophages from old mice and in livers from elderly humans that is associated with increased steatosis and fibrosis in middle-aged (MA) and old mice. MA mice that lack GPR18 on myeloid cells had exacerbated steatosis and hepatic fibrosis, which was associated with a decline in Mac2+ macrophages. Treatment of MA mice with RvD2 reduced steatosis and decreased hepatic fibrosis, correlating with increased Mac2+ macrophages, monocyte-derived macrophages and elevated numbers of monocytes in the liver, blood, and bone marrow. RvD2 acted directly upon the bone marrow to increase monocyte-macrophage progenitors. Using a transplantation assay we further demonstrated that bone marrow from old mice facilitated hepatic collagen accumulation in young mice, and transient RvD2 treatment to mice transplanted with bone marrow from old mice prevented hepatic collagen accumulation. Together, our study demonstrates that RvD2-GPR18 signaling controls steatosis and fibrosis and provides a mechanistic-based therapy for promoting liver repair in aging.

physiology↗

bioRxiv2022

Co-infection of Ehrlichia with B. burgdorferi drives emergency myelopoiesis and promotes Lyme arthritis

Lyme disease is caused by the extracellular pathogen Borrelia burgdorferi (Bb), transmitted by the Ixodes scapularis tick. Approximately one-third of infected individuals develop arthritis of weight-bearing joints, though it is unclear why some patients develop arthritis and severe systemic disease while others do not. C57BL/6 (B6) mice are susceptible to Bb infection but do not develop arthritis, providing an in vivo model to evaluate mechanisms regulating development of Lyme arthritis. We demonstrate here that co-infection of B6 mice with the tick-borne pathogens Bb and Ehrlichia muris (Em) induced significant arthritis. Although co-infection did not impact bacterial burden or growth of either pathogen, the resultant Lyme arthritis in co-infected mice correlated with significant hematologic disturbances. Whereas single Bb infection elicited no overt hematologic changes, Em infection resulted in thrombocytopenia, lymphopenia, monocytosis, and granulocytosis, which was consistently observed in mice co-infected with both Bb and Em. Hematologic changes correlated with profound changes to the hematopoietic stem and progenitor cell (HSPC) populations in Em-infected mice. Most notable were dramatic reductions in populations of HSPCs committed to myeloid-biased differentiation. Co-infection resulted in persistent hematologic changes and bone marrow inflammation. Our data demonstrate for the first time that B6 mice, resistant to developing Lyme arthritis, exhibit severe joint pathology in the presence of a second pathogen, correlating with persistent emergency myelopoiesis. Our data support the conclusion that pathogen burden is not sufficient for disease and specific inflammatory signals and cells regulate the development of Lyme arthritis. ImportanceTick-borne illnesses, historically relegated to specific geographic areas, are increasing in prevalence and distribution. Borrelia burgdorferi causes Lyme disease, the most common tick-borne illness in North America, characterized by debilitating arthritis, carditis, and neurologic complications. It remains unclear why certain infected individuals develop severe disease while others are only mildly symptomatic. Human monocytic ehrlichiosis (HME) is another tick-borne disease that often results in profound illness and severe hematological disturbances. We show here that co-infection of B6 mice, resistant to Lyme arthritis, with Borrelia burgdorferi and Ehrlichia muris, used to model HME, results in the development of severe arthritis and emergency myelopoiesis. Our work suggests that immune activation driven by co-infection contributes to the development of Lyme arthritis.

immunology↗