Comparative single-cell analysis reveals IFN-γ as a driver of respiratory sequelae after acute COVID-19.

Postacute sequelae of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection (PASC) represent an urgent public health challenge and are estimated to affect more than 60 million individuals globally. Although a growing body of evidence suggests that dysregulated immune reactions may be linked with PASC symptoms, most investigations have primarily centered around blood-based studies, with few focusing on samples derived from affected tissues. Furthermore, clinical studies alone often provide correlative insights rather than causal mechanisms. Thus, it is essential to compare clinical samples with relevant animal models and conduct functional experiments to understand the etiology of PASC. In this study, we comprehensively compared bronchoalveolar lavage fluid single-cell RNA sequencing data derived from clinical PASC samples and a mouse model of PASC. This revealed a pro-fibrotic monocyte-derived macrophage response in respiratory PASC, as well as abnormal interactions between pulmonary macrophages and respiratory resident T cells, in both humans and mice. Interferon-γ (IFN-γ) emerged as a key node mediating the immune anomalies in respiratory PASC. Neutralizing IFN-γ after the resolution of acute SARS-CoV-2 infection reduced lung inflammation and tissue fibrosis in mice. Together, our study underscores the importance of performing comparative analysis to understand the cause of PASC and suggests that the IFN-γ signaling axis might represent a therapeutic target.

Proximal immune-epithelial progenitor interactions drive chronic tissue sequelae post COVID-19.

The long-term physiological consequences of SARS-CoV-2, termed Post-Acute Sequelae of COVID-19 (PASC), are rapidly evolving into a major public health concern. The underlying cellular and molecular etiology remain poorly defined but growing evidence links PASC to abnormal immune responses and/or poor organ recovery post-infection. Yet, the precise mechanisms driving non-resolving inflammation and impaired tissue repair in the context of PASC remain unclear. With insights from three independent clinical cohorts of PASC patients with abnormal lung function and/or viral infection-mediated pulmonary fibrosis, we established a clinically relevant mouse model of post-viral lung sequelae to investigate the pathophysiology of respiratory PASC. By employing a combination of spatial transcriptomics and imaging, we identified dysregulated proximal interactions between immune cells and epithelial progenitors unique to the fibroproliferation in respiratory PASC but not acute COVID-19 or idiopathic pulmonary fibrosis (IPF). Specifically, we found a central role for lung-resident CD8+ T cell-macrophage interactions in maintaining Krt8hi transitional and ectopic Krt5+ basal cell progenitors, thus impairing alveolar regeneration and driving fibrotic sequelae after acute viral pneumonia. Mechanistically, CD8+ T cell derived IFN-γ and TNF stimulated lung macrophages to chronically release IL-1ß, resulting in the abnormal accumulation of dysplastic epithelial progenitors and fibrosis. Notably, therapeutic neutralization of IFN-γ and TNF, or IL-1ß after the resolution of acute infection resulted in markedly improved alveolar regeneration and restoration of pulmonary function. Together, our findings implicate a dysregulated immune-epithelial progenitor niche in driving respiratory PASC. Moreover, in contrast to other approaches requiring early intervention, we highlight therapeutic strategies to rescue fibrotic disease in the aftermath of respiratory viral infections, addressing the current unmet need in the clinical management of PASC and post-viral disease.

Proximal immune-epithelial progenitor interactions drive chronic tissue sequelae post COVID-19.

The long-term physiological consequences of SARS-CoV-2, termed Post-Acute Sequelae of COVID-19 (PASC), are rapidly evolving into a major public health concern. The underlying cellular and molecular etiology remain poorly defined but growing evidence links PASC to abnormal immune responses and/or poor organ recovery post-infection. Yet, the precise mechanisms driving non-resolving inflammation and impaired tissue repair in the context of PASC remain unclear. With insights from three independent clinical cohorts of PASC patients with abnormal lung function and/or viral infection-mediated pulmonary fibrosis, we established a clinically relevant mouse model of post-viral lung sequelae to investigate the pathophysiology of respiratory PASC. By employing a combination of spatial transcriptomics and imaging, we identified dysregulated proximal interactions between immune cells and epithelial progenitors unique to the fibroproliferation in respiratory PASC but not acute COVID-19 or idiopathic pulmonary fibrosis (IPF). Specifically, we found a central role for lung-resident CD8+ T cell-macrophage interactions in maintaining Krt8hi transitional and ectopic Krt5+ basal cell progenitors, thus impairing alveolar regeneration and driving fibrotic sequelae after acute viral pneumonia. Mechanistically, CD8+ T cell derived IFN-γ and TNF stimulated lung macrophages to chronically release IL-1ß, resulting in the abnormal accumulation of dysplastic epithelial progenitors and fibrosis. Notably, therapeutic neutralization of IFN-γ and TNF, or IL-1ß after the resolution of acute infection resulted in markedly improved alveolar regeneration and restoration of pulmonary function. Together, our findings implicate a dysregulated immune-epithelial progenitor niche in driving respiratory PASC. Moreover, in contrast to other approaches requiring early intervention, we highlight therapeutic strategies to rescue fibrotic disease in the aftermath of respiratory viral infections, addressing the current unmet need in the clinical management of PASC and post-viral disease.

Single cell RNA sequencing unravels mechanisms underlying senescence-like phenotypes of alveolar macrophages.

Alveolar macrophages (AMs) are resident innate immune cells that play vital roles in maintaining lung physiological functions. However, the effects of aging on their dynamics, heterogeneity, and transcriptional profiles remain to be fully elucidated. Through single cell RNA sequencing (scRNA-seq), we identified CBFß as an indispensable transcription factor that ensures AM self-renewal. Intriguingly, despite transcriptome similarities of proliferating cells, AMs from aged mice exhibited reduced embryonic stem cell-like features. Aged AMs also displayed compromised DNA repair abilities, potentially leading to obstructed cell cycle progression and an elevation of senescence markers. Consistently, AMs from aged mice exhibited impaired self-renewal ability and reduced sensitivity to GM-CSF. Decreased CBFß was observed in the cytosol of AMs from aged mice. Similar senescence-like phenotypes were also found in human AMs. Taken together, these findings suggest that AMs in aged hosts demonstrate senescence-like phenotypes, potentially facilitated by the abrogated CBF ß activity.

Inhibition of the mitochondrial pyruvate carrier simultaneously mitigates hyperinflammation and hyperglycemia in COVID-19.

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.

Host Recovery from Respiratory Viral Infection.

Emerging and re-emerging respiratory viral infections pose a tremendous threat to human society, as exemplified by the ongoing COVID-19 pandemic. Upon viral invasion of the respiratory tract, the host initiates coordinated innate and adaptive immune responses to defend against the virus and to promote repair of the damaged tissue. However, dysregulated host immunity can also cause acute morbidity, hamper lung regeneration, and/or lead to chronic tissue sequelae. Here, we review our current knowledge of the immune mechanisms regulating antiviral protection, host pathogenesis, inflammation resolution, and lung regeneration following respiratory viral infections, mainly using influenza virus and SARS-CoV-2 infections as examples. We hope that this review sheds light on future research directions to elucidate the cellular and molecular cross talk regulating host recovery and to pave the way to the development of pro-repair therapeutics to augment lung regeneration following viral injury.

COVID-19 immunopathology: From acute diseases to chronic sequelae.

The clinical manifestation of coronavirus disease 2019 (COVID-19) mainly targets the lung as a primary affected organ, which is also a critical site of immune cell activation by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). However, recent reports also suggest the involvement of extrapulmonary tissues in COVID-19 pathology. The interplay of both innate and adaptive immune responses is key to COVID-19 management. As a result, a robust innate immune response provides the first line of defense, concomitantly, adaptive immunity neutralizes the infection and builds memory for long-term protection. However, dysregulated immunity, both innate and adaptive, can skew towards immunopathology both in acute and chronic cases. Here we have summarized some of the recent findings that provide critical insight into the immunopathology caused by SARS-CoV-2, in acute and post-acute cases. Finally, we further discuss some of the immunomodulatory drugs in preclinical and clinical trials for dampening the immunopathology caused by COVID-19.

Immune determinants of chronic sequelae after respiratory viral infection.

The acute effects of various respiratory viral infections have been well studied, with extensive characterization of the clinical presentation as well as viral pathogenesis and host responses. However, over the course of the recent COVID-19 pandemic, the incidence and prevalence of chronic sequelae after acute viral infections have become increasingly appreciated as a serious health concern. Post-acute sequelae of COVID-19, alternatively described as "long COVID-19," are characterized by symptoms that persist for longer than 28 days after recovery from acute illness. Although there exists substantial heterogeneity in the nature of the observed sequelae, this phenomenon has also been observed in the context of other respiratory viral infections including influenza virus, respiratory syncytial virus, rhinovirus, severe acute respiratory syndrome coronavirus, and Middle Eastern respiratory syndrome coronavirus. In this Review, we discuss the various sequelae observed following important human respiratory viral pathogens and our current understanding of the immunological mechanisms underlying the failure of restoration of homeostasis in the lung.

Downregulation of transcriptional activity, increased inflammation, and damage in the placenta following in utero Zika virus infection is associated with adverse pregnancy outcomes.

Zika virus (ZIKV) infection during pregnancy causes serious adverse outcomes to the developing fetus, including fetal loss and birth defects known as congenital Zika syndrome (CZS). The mechanism by which ZIKV infection causes these adverse outcomes and specifically, the interplay between the maternal immune response and ZIKV replication has yet to be fully elucidated. Using an immunocompetent mouse model of transplacental ZIKV transmission and adverse pregnancy outcomes, we have previously shown that Asian lineage ZIKV disrupts placental morphology and induces elevated secretion of IL-1ß. In the current manuscript, we characterized placental damage and inflammation during in utero African lineage ZIKV infection. Within 48 hours after ZIKV infection at embryonic day 10, viral RNA was detected in placentas and fetuses from ZIKA infected dams, which corresponded with placental damage and reduced fetal viability as compared with mock infected dams. Dams infected with ZIKV had reduced proportions of trophoblasts and endothelial cells and disrupted placental morphology compared to mock infected dams. While placental IL-1ß was increased in the placenta, but not the spleen, within 3 hours post infection, this was not caused by activation of the NLRP3 inflammasome. Using bulk mRNAseq from placentas of ZIKV and mock infected dams, ZIKV infection caused profound downregulation of the transcriptional activity of genes that may underly tissue morphology, neurological development, metabolism, cell signaling and inflammation, illustrating that in utero ZIKV infections causes disruption of pathways associated with CZS in our model.

Anticoagulation in COVID-19: a review of current literature and guidelines.

Severe acute respiratory syndrome coronavirus 2 infections are associated with greater risk of both arterial and venous thromboembolic events.Pathophysiology and Clinical implications: This has been attributed to a florid proinflammatory state resulting in microvascular dysfunction, activation of platelets and procoagulant systems as well as possible direct endothelial injury. The associated morbidity and mortality of these events has prompted much speculation and varied anticoagulation and fibrinolytic strategies based on multiple criteria including disease severity and biomarkers. No clear definitive benefit has been established with these approaches, which have frequently led to greater bleeding complications without significant mortality benefit.Overview: In this review, we outline the burden of these thromboembolic events in coronavirus disease-2019 (COVID-19) as well as the hypothesized contributory biological mechanisms. Finally, we provide a brief overview of the major clinical studies on the topic, and end with a summary of major societal guideline recommendations on anticoagulation in COVID-19.

Therapeutic angiogenesis in coronary artery disease: a review of mechanisms and current approaches.

INTRODUCTION: Despite tremendous advances, the shortcomings of current therapies for coronary disease are evidenced by the fact that it remains the leading cause of death in many parts of the world. There is hence a drive to develop novel therapies to tackle this disease. Therapeutic approaches to coronary angiogenesis have long been an area of interest in lieu of its incredible, albeit unrealized potential. AREAS COVERED: This paper offers an overview of mechanisms of native angiogenesis and a description of angiogenic growth factors. It progresses to outline the advances in gene and stem cell therapy and provides a brief description of other investigational approaches to promote angiogenesis. Finally, the hurdles and limitations unique to this particular area of study are discussed. EXPERT OPINION: An effective, sustained, and safe therapeutic option for angiogenesis truly could be the paradigm shift for cardiovascular medicine. Unfortunately, clinically meaningful therapeutic options remain elusive because promising animal studies have not been replicated in human trials. The sheer complexity of this process means that numerous major hurdles remain before therapeutic angiogenesis truly makes its way from the bench to the bedside.

Young at Gut-Turning Back the Clock with the Gut Microbiome.

Over the past century, we have witnessed an increase in life-expectancy due to public health measures; however, we have also seen an increase in susceptibility to chronic disease and frailty. Microbiome dysfunction may be linked to many of the conditions that increase in prevalence with age, including type 2 diabetes, cardiovascular disease, Alzheimer's disease, and cancer, suggesting the need for further research on these connections. Moreover, because both non-modifiable (e.g., age, sex, genetics) and environmental (e.g., diet, infection) factors can influence the microbiome, there are vast opportunities for the use of interventions related to the microbiome to promote lifespan and healthspan in aging populations. To understand the mechanisms mediating many of the interventions discussed in this review, we also provide an overview of the gut microbiome's relationships with the immune system, aging, and the brain. Importantly, we explore how inflammageing (low-grade chronic inflammation that often develops with age), systemic inflammation, and senescent cells may arise from and relate to the gut microbiome. Furthermore, we explore in detail the complex gut-brain axis and the evidence surrounding how gut dysbiosis may be implicated in several age-associated neurodegenerative diseases. We also examine current research on potential interventions for healthspan and lifespan as they relate to the changes taking place in the microbiome during aging; and we begin to explore how the reduction in senescent cells and senescence-associated secretory phenotype (SASP) interplay with the microbiome during the aging process and highlight avenues for further research in this area.

Role of Inflammation in Virus Pathogenesis during Pregnancy.

Viral infections during pregnancy lead to a spectrum of maternal and fetal outcomes, ranging from asymptomatic disease to more critical conditions presenting with severe maternal morbidity, stillbirth, preterm birth, intrauterine growth restriction, and fetal congenital anomalies, either apparent at birth or later in life. In this article, we review the pathogenesis of several viral infections that are particularly relevant in the context of pregnancy and intrauterine inflammation. Understanding the diverse mechanisms employed by viral pathogens as well as the repertoire of immune responses induced in the mother may help to establish novel therapeutic options to attenuate changes in the maternal-fetal interface and prevent adverse pregnancy outcomes.

Animal models of congenital zika syndrome provide mechanistic insight into viral pathogenesis during pregnancy.

In utero Zika virus (ZIKV; family Flaviviridae) infection causes a distinct pattern of birth defects and disabilities in the developing fetus and neonate that has been termed congenital zika syndrome (CZS). Over 8,000 children were affected by the 2016 to 2017 ZIKV outbreak in the Americas, many of whom developed CZS as a result of in utero exposure. To date, there is no consensus about how ZIKV causes CZS; animal models, however, are providing mechanistic insights. Using nonhuman primates, immunocompromised mice, immunocompetent mice, and other animal models (e.g., pigs, sheep, guinea pigs, and hamsters), studies are showing that maternal immunological responses, placental infection and inflammation, as well as viral genetic factors play significant roles in predicting the downstream consequences of in utero ZIKV infection on the development of CZS in offspring. There are thousands of children suffering from adverse consequences of CZS. Therefore, the animal models developed to study ZIKV-induced adverse outcomes in offspring could provide mechanistic insights into how other viruses, including influenza and hepatitis C viruses, impact placental viability and fetal growth to cause long-term adverse outcomes in an effort to identify therapeutic treatments.

Dose-dependent structural and immunological changes in the placenta and fetal brain in response to systemic inflammation during pregnancy.

PROBLEM: Systemic maternal inflammation is associated with adverse neonatal sequelae. We tested the hypothesis that IL-1ß is a key inflammatory regulator of adverse pregnancy outcomes. METHOD OF STUDY: Pregnant mice were treated with intraperitoneal injections of IL-1ß (0, 0.1, 0.5, or 1 µg) from embryonic day (E)14 to E17. Placenta and fetal brains were harvested and analyzed for morphologic changes and IL-1ß signaling markers. RESULTS: As compared with non-treated dams, maternal injections with IL-1ß resulted in increased p-NF-κB and caspase-1 in placentas and fetal brains, but not consistently in spleens, suggesting induction of intrinsic IL-1ß production. These findings were confirmed by increased levels of IL-1ß in the placentas of the IL-1ß-treated dams. Systemic treatment of dams with IL-1ß suppressed Stat1 signaling. Maternal inflammation caused by IL-1ß treatment reduced fetal viability to 80.6% and 58.9%, in dams treated with either 0.5 or 1 µg of IL-1ß, respectively. In the placentas, there was an IL-1ß dose-dependent distortion of the labyrinth structure, decreased numbers of mononuclear trophoblast giant cells, and reduced proportions of endothelial cells as compared to placentas from control dams. In fetal brains collected at E17, there was an IL-1ß dose-dependent reduction in cortical neuronal morphology. CONCLUSION: This work demonstrates that systemic IL-1ß injection causes dose-dependent structural and functional changes in the placenta and fetal brain.