Citations

Aging is a major risk factor for increased morbidity and mortality following acute respiratory virus infections. To elucidate the immune determinants underlying viral pathogenesis and delayed lung repair in the aged lung, a comprehensive time-course study was conducted. Single-cell RNA sequencing (scRNAseq) and high-dimensional flow cytometry were utilized to compare lungs from young and aged mice infected with influenza A virus (IAV). Aged hosts displayed diminished alveolar macrophage (AM) and dendritic cell (DC) but elevated monocyte-derived macrophage (MoM) and interstitial macrophage (IM) presence following infection. Additionally, enhanced accumulation of adaptive immune cells, including CD4+ tissue-resident helper (TRH) cells, CD8+ tissue-resident memory (TRM) cells, and a B cell subset resembling age-associated B cells, was observed in the memory phase. Pathway analysis revealed that elevated type I and II interferon (IFNα/γ) signaling, especially in MoM/IM subsets, distinguished the aged hosts from the young. Inhibition of IFNα/γ signaling after viral clearance improved long-term respiratory outcomes and reduced both IM and TRH populations in aged mice. These findings highlight the pivotal role of IFNα/γ signaling, likely within MoM/IM subsets, in driving the exuberant persistence of adaptive immune cells and chronic immunopathology in the aged lung following acute viral infection.

Aging is a major risk factor for increased morbidity and mortality following acute respiratory virus infections. To elucidate the immune determinants underlying viral pathogenesis and delayed lung repair in the aged lung, a comprehensive time-course study was conducted. Single-cell RNA sequencing (scRNAseq) and high-dimensional flow cytometry were utilized to compare lungs from young and aged mice infected with influenza A virus (IAV). Aged hosts displayed diminished alveolar macrophage (AM) and dendritic cell (DC) but elevated monocyte-derived macrophage (MoM) and interstitial macrophage (IM) presence following infection. Additionally, enhanced accumulation of adaptive immune cells, including CD4+ tissue-resident helper (TRH) cells, CD8+ tissue-resident memory (TRM) cells, and a B cell subset resembling age-associated B cells, was observed in the memory phase. Pathway analysis revealed that elevated type I and II interferon (IFNα/γ) signaling, especially in MoM/IM subsets, distinguished the aged hosts from the young. Inhibition of IFNα/γ signaling after viral clearance improved long-term respiratory outcomes and reduced both IM and TRH populations in aged mice. These findings highlight the pivotal role of IFNα/γ signaling, likely within MoM/IM subsets, in driving the exuberant persistence of adaptive immune cells and chronic immunopathology in the aged lung following acute viral infection.

Abstract Aging is considered to be a major risk factor for host morbidity and mortality upon acute respiratory virus infections. To better elucidate the immune determinants of viral pathogenesis during aging, we chronological characterized lung cellular and molecular profiles following influenza virus (PR8) infection in young or aged mice till 60 days post infection. Time-course scRNAseq coupled with high dimensional flow cytometry enabled the description of changes in both immune and stromal compartment between young and aged hosts. We further zoomed into the myeloid compartment and focused on the dynamic responses of lung macrophages given their complex roles in viral pathogenesis, tissue repair and lung fibrosis. Enlarged Monocyte-derived Macrophage (MoM) population as well as decreased resident-Alveolar Macrophage (AM) population were observed in the aged mice when compared to those of the young mice. Despite the self-sustain nature of AMs during homeostasis, it has been reported that Ly6Chi monocytes can gain AM identity following severe lung damage like influenza virus infection. We found that the gain of AM identity from monocytes was abrogated in the aged hosts, which likely contributed to the age-associated impairment in lung recovery after influenzas virus infection. Additionally, trajectory analysis with scRNAseq allowed us to identify IFNα/γ signaling to be potential pathways contributing to such defect. This notion is also supported by elevated IFNγ level in BAL from the aged host during lung recovery. Our results thus have improved our understanding on the cellular and molecular mechanisms by which aged hosts exhibit severe diseases and delayed recovery after respiratory viral infection.

The relationship between diabetes and coronavirus disease 2019 (COVID-19) is bidirectional: Although individuals with diabetes and high blood glucose (hyperglycemia) are predisposed to severe COVID-19, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection can also cause hyperglycemia and exacerbate underlying metabolic syndrome. Therefore, interventions capable of breaking the network of SARS-CoV-2 infection, hyperglycemia, and hyperinflammation, all factors that drive COVID-19 pathophysiology, are urgently needed. Here, we show that genetic ablation or pharmacological inhibition of mitochondrial pyruvate carrier (MPC) attenuates severe disease after influenza or SARS-CoV-2 pneumonia. MPC inhibition using a second-generation insulin sensitizer, MSDC-0602K (MSDC), dampened pulmonary inflammation and promoted lung recovery while concurrently reducing blood glucose levels and hyperlipidemia after viral pneumonia in obese mice. Mechanistically, MPC inhibition enhanced mitochondrial fitness and destabilized hypoxia-inducible factor–1α, leading to dampened virus-induced inflammatory responses in both murine and human lung macrophages. We further showed that MSDC enhanced responses to nirmatrelvir (the antiviral component of Paxlovid) to provide high levels of protection against severe host disease development after SARS-CoV-2 infection and suppressed cellular inflammation in human COVID-19 lung autopsies, demonstrating its translational potential for treating severe COVID-19. Collectively, we uncover a metabolic pathway that simultaneously modulates pulmonary inflammation, tissue recovery, and host metabolic health, presenting a synergistic therapeutic strategy to treat severe COVID-19, particularly in patients with underlying metabolic disease.

Abstract Aging has been shown to be one of the major risk factors for host morbidity and mortality following infections with respiratory viruses including influenza virus and SARS-CoV-2. The unique immune properties of the aged hosts not only influence pathogen clearance and tissue damage responses, but also modulate the pathogenesis of the long-term sequalae post acute viral clearance. Currently, the dynamics and features of mucosal immune responses following acute respiratory viral infections in the aged hosts remain to be fully elucidated. Here, we characterized the lung cellular and molecular profiles following influenza virus infection in young (~3-month-old) or aged (~24-month-old) mice with a chronological manner from acute to chronic phase. Using DNA-oligo-conjugated CD45 antibody and i.v. labeling, we were able to distinguish the unique responses of circulating vs lung-resident immune cells to influenza virus infection during aging. These responses were further validated by spectral flow cytometry analysis of the lung innate and adaptive immune cells. Further data analysis and integration are warranted for this unique large data set detailing the single cell molecular profiles of mucosal responses to influenza virus infection comparing young and aged hosts.

Abstract Fetal-derived tissue-resident macrophages exhibit stem cell-like features of self-renewal in adulthood to maintain macrophage population during homeostasis and/or various insults. However, little is known about the cellular and molecular mechanisms modulating proliferative and inflammatory fate decisions of tissue-resident macrophages in vivo. Here, we show that WNT-β-catenin signaling inhibited lung-resident alveolar macrophage (AM) self-renewal, while simultaneously promoted AM inflammatory activities in vitro and in vivo during influenza virus infection. Mechanistically, WNT engagement facilitated the binding of β-catenin with HIF-1α over its conventional binding partner TCF-4. Such a binding choice led to the elevated macrophage inflammation in a glycolysis-dependent manner, while inhibited AM self-renewal by causing mitochondrial damage and impairing oxidative phosphorylation. Thus, AM self-renewal and inflammatory activity are uncoupled by WNT-β-catenin signaling through HIF-1α-mediated cellular metabolic choice. Importantly, we showed that AM with high HIF-1α activity had limited proliferative capacity and produced inflammatory cytokines, while AM with low HIF-1α activity were highly proliferative and expressed genes associated with tissue repair function in vivo during influenza virus infection. In accordance, we demonstrated that AM proliferation and repopulation were needed for optimal lung repair following the clearance of influenza virus in the respiratory tract. Our results have revealed key mechanisms modulating macrophage fate choice between progeny production versus inflammatory effector activity, and subsequent effects on tissue inflammation and repair.

Abstract Alveolar Macrophages (AMs) are unique innate immune cells that reside in the alveolar space and accommodate the ever-changing need of the lungs against internal and external challenges. During homeostasis, AMs maintained themselves through self-renewal without the need for input from adult hematopoietic stem cells. Currently, little is known about how aging influences AM dynamics, heterogeneity and self-renewal. To this end, we have performed single-cell RNA sequencing (scRNA-seq) on murine lung AMs (CD11+ Siglec F+) isolated from young (~8w) and aged (~2y) mice. We discovered that despite similar transcriptome in the proliferating cells, AMs from aged mice had reduced proliferation and self-renew ability than those from the young mice. AMs from aged mice also displayed elevated senescence markers such as p16, p21 and p53. Consistently, AMs from aged mice had reduced DNA repair ability, which could contribute to their impaired capacity to pass through the cell cycle checkpoints. Interestingly, AMs from aged mice also possessed reduced pro-apoptotic gene profile. Thus, we hypothesize that the reduced proliferation- and apoptosis-associated gene profiles in aged AMs may lead to the enhanced senescence-like phenotype in those cells. Further validation of the senescence-like phenotype of aged AMs and investigation of how they contribute to lung “inflammaging” are warranted.

Abstract Alveolar Macrophages (AMs) are a unique population of innate immune cells that reside in the alveolar space and contribute to accommodate the ever-changing need of the lungs against the external environmental challenges. AMs derive from the fetal origins and are capable of maintaining themselves through self-renewal without the input of hematopoiesis during the adulthood. However, little is known about how aging is influencing the molecular characteristics and heterogeneity of the AMs during homeostasis. Using single-cell RNA sequencing (scRNA-seq) and Seurat clustering, we discovered AMs can be subdivided into different “subsets” with unique molecular characteristics during homeostasis. Interestingly, when we further investigate the AM population with the combined data from the young(~8w) and old(~2y) mice, the data suggested that the proliferating cell fall in the same cluster with reduced number in the old-mice group, while the poised inflammatory cells showed distinct molecular patterns between the group with different age. We hypothesize that the inflammatory and the self-renewal AM subpopulations may be maintained by distinct extracellular signals. With the progress of aging, the self-renewal ability of AMs would reduce because of the number of proliferating cells but not the change of molecular patterns. At the same time, the inflammatory population would change its characteristics with age, and potentially lead to functional change upon activation. Further validation of the AM subset identity as well as the developmental and functional interrelationship of these subsets are required. In addition, the extrinsic and intrinsic signals responsible for the maintenance of these AM subsets are to be explored.

Neutrophils are vital for antimicrobial defense; however, their role during viral infection is less clear. Furthermore, the molecular regulation of neutrophil fate and function at the viral infected sites is largely elusive. Here we report that BCL6 deficiency in myeloid cells exhibited drastically enhanced host resistance to severe influenza A virus (IAV) infection. In contrast to the notion that BCL6 functions to suppress innate inflammation, we find that myeloid BCL6 deficiency diminished lung inflammation without affecting viral loads. Using a series of Cre-transgenic, reporter, and knockout mouse lines, we demonstrate that BCL6 deficiency in neutrophils, but not in monocytes or lung macrophages, attenuated host inflammation and morbidity following IAV infection. Mechanistically, BCL6 bound to the neutrophil gene loci involved in cellular apoptosis in cells specifically at the site of infection. As such, BCL6 disruption resulted in increased expression of apoptotic genes in neutrophils in the respiratory tract, but not in the circulation or bone marrow. Consequently, BCL6 deficiency promoted tissue neutrophil apoptosis. Partial neutrophil depletion led to diminished pulmonary inflammation and decreased host morbidity. Our results reveal a previously unappreciated role of BCL6 in modulating neutrophil apoptosis at the site of infection for the regulation of host disease development following viral infection. Furthermore, our studies indicate that tissue-specific regulation of neutrophil survival modulates host inflammation and tissue immunopathology during acute respiratory viral infection.

Respiratory viral infections, like IAV and respiratory syncytial virus (RSV) infections, impose great challenges to public health. Alveolar macrophages (AM) are lung-resident immune cells that play important roles in protecting the host against IAV and RSV infections. However, the underlying molecular mechanisms by which AM modulate host inflammation, disease development, and tissue recovery are not very well understood. Here we identify that PPAR-γ expression in AM is crucial to suppress pulmonary inflammation and diseases and to promote fast host recovery from IAV and RSV infections. Our data suggest that targeting macrophage PPAR-γ may be a promising therapeutic option in the future to suppress acute inflammation and simultaneously promote recovery from severe diseases associated with respiratory viral infections.