Seasonal influenza epidemics, with influenza A virus (IAV) being the most prevalent species, are estimated to result in 3-5 million severe illnesses and 300,000-650,000 deaths globally each year (1). Despite the COVID-19 pandemic, these influenza epidemics continue to represent a significant financial burden and a major global health threat. Seasonal viruses naturally mutate and consistently circulate (2), generating strains resistant to existing vaccines or antiviral therapies (3–5).
In response to IAV infection and subsequent replication, infected airway epithelial cells and activated lung-resident immune cells release inflammatory cytokines and chemokines to initiate a robust influx of innate immune cells, such as neutrophils, monocytes and macrophages into the lung (6). While the initial responses of neutrophils and macrophages are essential for IAV clearance, dysregulated and persistent inflammatory cell recruitment mediating uncontrolled inflammation leads to pulmonary damage and increased morbidity and mortality (7, 8). Therefore, identifying key regulators controlling excessive immune cell recruitment and the subsequent proinflammatory cytokine storm bears significance in the development of strategies for the treatment of influenza infections.
Regulator of G-protein signaling (RGS) proteins represent a superfamily of proteins defined by the presence of RGS domain, which is known to bind and deactivate heterotrimeric G-protein subunits (9, 10). Classically, RGS proteins modulate the magnitude and duration of G protein-coupled receptor (GPCR) signaling through heterotrimeric G-protein inactivation by accelerating the intrinsic GTPase activity of Gα-subunits to enhance the hydrolysis of the active guanosine triphosphate (GTP)-bound Gα subunits to inactive guanosine diphosphate (GDP)-bound Gα proteins (9–11). Because of the involvement of GPCRs and G-protein signaling in diverse systems, RGS proteins have emerged to mediate essential roles in regulation of physiological and pathological processes (12).
Among RGS proteins, RGS10, a member of the D/R12 subfamily, is one of the smallest RGS proteins that lacks structural domains and functional motifs outside of the RGS domain (13). RGS10 selectively functions as a GTPase activating protein (GAP) for Gαi family of G-proteins (11, 14, 15), and is highly expressed in the central nervous system (CNS) and immune system (16). Within the immune system, RGS10 has high levels of expression in spleen, lymph nodes, and the bone marrow as well as subsets of leukocytes including monocytes (17), tissue resident and recruited macrophages (18–20), dendritic cells (21), and T lymphocytes (22).
Independent of its GAP function, RGS10 demonstrates profound, in vitro, anti-inflammatory effect by regulating macrophages activation. Strikingly, loss of RGS10 in macrophages results in amplification of NF-κB transcriptional activity and the generation of pro-inflammatory mediators, such as tumor necrosis factor-alpha (TNF-α), interleukins, and cyclooxygenase-2 (COX-2)-mediated prostaglandin E2 (PGE2), and inducible nitric oxide synthase (iNOS) upon toll-like receptor 4 (TLR4) activation (18–20, 23, 24). Further, following macrophage activation, RGS10 acts as a key factor in the regulation of macrophage polarization by suppressing classical M1 activation and promoting alternative M2 activation (19). In addition to macrophages, RGS10 regulates chemotaxis and adhesion of T cells in response to chemokine signals (22). While these observations propose a role of RGS10 in controlling immune cell activation, it remains unknow whether RGS10 plays a role in limiting exacerbated immune responses in respiratory infections including lethal influenza A viral infection.
In this study, our goal is to determine the in vivo biological role of RGS10 in IAV infection. Owing to the high expression of RGS10 in immune cells and its regulatory role in inflammatory responses, we predict that RGS10 has a physiological function in respiratory IAV infection. We hypothesize that Rgs10 deficiency results in a prolonged and exacerbated inflammatory response associated with more severe clinical outcomes in a mouse model of influenza lung infection. Our results show that Rgs10-deficient mice are more susceptible to IAV infection than control mice. Significantly higher mortality, morbidity, lung viral loads and inflammation were observed in infected Rgs10-deficient mice compared to infected wild-type mice indicating a novel, beneficial role of RGS10 in the immune system, specifically respiratory antiviral responses.