Dos Santos Pereira Andrade, A. C.

bioRxiv2026

The orphan receptor IL-17RD is a negative regulator of RIG-I-like receptor-dependent antiviral innate immunity and restrains SARS-CoV-2-induced lung inflammation

Detection of viral RNA by the RIG-I-like receptors (RLRs) RIG-I and MDA5 triggers assembly of a MAVS-dependent signalosome that activates the TBK1-IRF3 and IKK{beta}-NF-{kappa}B axes together with the JNK and p38 MAPK modules, driving type I and type III interferon (IFN) and inflammatory cytokine production. Because unrestrained activity of this pathway is a major cause of immunopathology, host-encoded negative regulators are essential, yet the full complement of these brakes remains incompletely defined. Here we identify interleukin-17 receptor D (IL-17RD, also known as SEF), an orphan member of the IL-17 receptor family previously characterized as an antagonist of FGF and Toll-like receptor signaling, as a negative regulator of RLR-driven antiviral innate immunity. Using a CRISPR-engineered and shRNA-depleted human airway epithelial-derived lung carcinoma A549 cell line, we show that loss of IL-17RD amplifies and prolongs phosphorylation of TBK1 and IRF3 in response to poly I:C transfection and to infection with encephalomyocarditis virus (EMCV) or Sendai virus (SeV), and likewise potentiates the IKK{beta}-I{kappa}B module and the TAK1-JNK1/2 and p38 MAPK branches. This translates into increased nuclear accumulation of IRF3 and p65, and markedly elevated induction of IFNB1, IFNL1-3, CCL5, IL6, and NFKBIA transcripts, as well as secreted IFN-{beta} and IL-6. Silencing IL-17RD in ACE2-expressing A549 cells similarly derepresses the antiviral and inflammatory transcriptional programme following SARS-CoV-2 infection. Epistasis experiments place IL-17RD at the level of MAVS, downstream of the RLR sentinels. Mechanistically, IL-17RD localizes to the ER-to-Golgi intermediate compartment (ERGIC), the membrane platform on which the MAVS signalosome is present, and associates with RIG-I, MDA5, MAVS, TBK1 and IRF3. Its re-expression in depleted cells redistributes RLR effectors and TRAF proteins across low-molecular-weight signalosome fractions, reducing the amount of IRF3 recruited to the 670 kDa MAVS signalosome complex. Complementation of IL-17RD-deficient cells also indicates that the intracellular TIR subdomain is sufficient to confer this antagonistic activity. Finally, Il17rd-/- mice display a splenic transcriptome enriched for antiviral response signatures, and, following intranasal infection with a moderate dose of SARS-CoV-2, they mount an exaggerated pulmonary cytokine response and develop significantly greater lung inflammation and fibrosis than wild-type littermates. Together, these data establish IL-17RD as a bona fide brake on the RLR-MAVS axis that limits virus-induced immunopathology, and identify the SEFIR/TIR subdomain as the module responsible for this activity.

microbiology↗

bioRxiv2024

Delayed viral clearance and altered inflammatory responses resulted in increased severity of SARS-CoV-2 infection in aged mice.

Since the onset of the COVID-19 pandemic, advanced age has emerged as a major predictor of disease severity. Epidemiological investigations consistently demonstrate an overrepresentation of the elderly in COVID-19 hospitalizations and fatalities. Despite this, a comprehensive understanding of the molecular mechanisms explaining how old age constitutes a critical risk factor remains elusive. To unravel this, we designed an animal study, juxtaposing the course of COVID-19 in young adults (2 months) and geriatric (15-22 months) mice. Both groups of K18(hACE2) mice were intranasally exposed to 500 TCID50 of the SARS-CoV-2 Delta variant with a variety of outcomes assessed on days 3, 5, and 7 post-infections (DPI). Analyses included pulmonary cytokines, RNA, viral loads, lipidomic profiles, and histological assessments, with a concurrent evaluation of the percentage of mice reaching humane endpoints. The findings unveiled notable distinctions between the two groups, with aged mice exhibiting impaired viral clearance at 7 DPI, correlating with diminished survival rates together with an absence of weight loss recovery at 6-7 DPI. Additionally, elderly-infected mice exhibited a deficient Th1 response characterized by diminished productions of IFNg, CCL2, CCL3, and CXCL9 relative to younger mice. Furthermore, mass-spectrometry analysis of the lung lipidome indicated altered expression of several lipids with immunomodulatory and pro-resolution effects in aged mice such as Resolvin, HOTrEs, and NeuroP, but also DiHOMEs-related ARDS. Collectively, disease severity implies a dysregulation of the antiviral response in elderly-infected mice relative to younger mice, resulting in compromised viral clearance and a more unfavorable prognosis. This underscores the potential efficacy of immunomodulatory treatments for elderly subjects experiencing symptoms of severe COVID-19. Author summaryIn this study, we investigated why older age is linked to more severe COVID-19 outcomes by comparing the progression of the disease in young (2 months) and elderly (15-22 months) K18(hACE2) mice infected with the SARS-CoV-2 Delta variant. After exposing both groups to the virus, we assessed various factors such as viral loads, immune responses, and lipid profiles in the lungs at different time points. Our findings revealed that elderly mice struggled to clear the virus by day 7 post-infection, leading to higher mortality rates and poorer recovery compared to younger mice. Aged mice showed weaker immune responses, with reduced production of key antiviral proteins like IFNg and certain chemokines. Lipid analysis also highlighted differences in molecules involved in immune regulation and lung protection, such as decreased levels of pro-resolving lipids and increased lipids associated with lung injury. These results suggest that older mice have a compromised antiviral defense, which could inform new therapeutic approaches for elderly patients with severe COVID-19.

microbiology↗