Prohibitin-1 and -2 have diverse cell-autonomous effects on inflammatory signaling

Abstract Prohibitins (PHB1 and PHB2) are proteins that assemble in hetero-oligomeric complexes within the mitochondrial inner membrane and in the plasma membrane lipid rafts where they are at the nexus of metabolic and pro-survival decisions including inflammation. We have recently observed that mice intraperitoneal (i.p.) injected with lipopolysaccharide (LPS) have increased serum prohibitin (PHB), and injection of recombinant PHB1 (rPHB1) post LPS rescues cardiac function. However, the role of PHB in the innate immune response to LPS is currently unknown. Using an in vivo model of sepsis, we injected C57Bl/6J mice i.p. with LPS and 3 subsequent doses of rPHB1. Blood was analyzed for immune cell characterization by flow cytometry, and liver, kidney and lung tissue were harvested for pro-inflammatory cytokine expression. Systemic LPS increased number of blood neutrophils (PMNs), PMN expression of the adhesion molecule CD11b, and tissue expression of TNF-α, IL-6, and IL-1β. Treatment with rPHB1 decreased blood PMN CD11b expression and expression of IL-6 in liver, kidney and lung tissues. To better characterize the role of PHB in immune cells, we knocked down PHB1 or PHB2 in RAW 264.7 macrophages. PHB1- or PHB2-deficient macrophages were then stimulated with LPS, and cell supernatant and lysate were collected for cytokine production. Cell lines deficient in PHB2 had decreased TNF-α compared to macrophages sufficient in PHBs. These data suggest PHB1 and -2 have differential and complex effects on the innate immune response. Cell-associated PHB is required for acute pro-inflammatory signaling responses to LPS that initiate the sepsis response, but extracellular PHB, released in the later phase of sepsis, may feedback to dampen the response.