We previously demonstrated a cardiac mitochondrial biogenic response in insulin resistant mice that requires the nuclear receptor transcription factor PPARα. We hypothesized that the PPARα coactivator peroxisome proliferator-activated receptor gamma coactivator-1 alpha (PGC-1α) is necessary for mitochondrial biogenesis in insulin resistant hearts and that this response was adaptive. Mitochondrial phenotype was assessed in insulin resistant mouse models in wild-type (WT) versus PGC-1α deficient (PGC-1α−/−) backgrounds. Both high fat-fed (HFD) WT and 6 week-old Ob/Ob animals exhibited a significant increase in myocardial mitochondrial volume density compared to standard chow fed or WT controls. In contrast, HFD PGC-1α−/− and Ob/Ob-PGC-1α−/− hearts lacked a mitochondrial biogenic response. PGC-1α gene expression was increased in 6 week-old Ob/Ob animals, followed by a decline in 8 week-old Ob/Ob animals with more severe glucose intolerance. Mitochondrial respiratory function was increased in 6 week-old Ob/Ob animals, but not in Ob/Ob-PGC-1α−/− mice and not in 8 week-old Ob/Ob animals, suggesting a loss of the early adaptive response, consistent with the loss of PGC-1α upregulation. Animals that were deficient for PGC-1α and heterozygous for the related coactivator PGC-1β (PGC-1α−/−β+/−) were bred to the Ob/Ob mice. Ob/Ob-PGC-1α−/−β+/− hearts exhibited dramatically reduced mitochondrial respiratory capacity. Finally, the mitochondrial biogenic response was triggered in H9C2 myotubes by exposure to oleate, an effect that was blunted with shRNA-mediated PGC-1 “knockdown”. We conclude that PGC-1 signaling is important for the adaptive cardiac mitochondrial biogenic response that occurs during the early stages of insulin resistance. This response occurs in a cell autonomous manner and likely involves exposure to high levels of free fatty acids.

BACKGROUND Circadian rhythms are evident in basic immune processes, but it is unclear if rhythms exist in clinical endpoints like vaccine protection. Here, we examined associations between COVID-19 vaccination timing and effectiveness. METHODS We retrospectively analyzed a large Israeli cohort with timestamped COVID-19 vaccinations ( n = 1,515,754 patients over 12 years old, 99.2% receiving BNT162b2). Endpoints included COVID-19 breakthrough infection and COVID-19–associated emergency department visits and hospitalizations. Our main comparison was among patients vaccinated during morning (800–1159 hours), afternoon (1200–1559 hours), or evening hours (1600–1959 hours). We employed Cox regression to adjust for differences in age, sex, and comorbidities. RESULTS Breakthrough infections differed based on vaccination time, with lowest the rates associated with late morning to early afternoon and highest rates associated with evening vaccination. Vaccination timing remained significant after adjustment for patient age, sex, and comorbidities. Results were consistent in patients who received the basic 2-dose series and who received booster doses. The relationship between COVID-19 immunization time and breakthrough infections was sinusoidal, consistent with a biological rhythm that modifies vaccine effectiveness by 8.6%–25%. The benefits of daytime vaccination were concentrated in younger (<20 years old) and older patients (>50 years old). COVID-19–related hospitalizations varied significantly with the timing of the second booster dose, an intervention reserved for older and immunosuppressed patients (HR = 0.64, morning vs. evening; 95% CI, 0.43–0.97; P = 0.038). CONCLUSION We report a significant association between the time of COVID-19 vaccination and its effectiveness. This has implications for mass vaccination programs. FUNDING NIH.

Asthma is a chronic disease of childhood, but for unknown reasons, disease activity sometimes subsides as children mature. In this study, we present clinical and animal model evidence suggesting that the age dependency of childhood asthma stems from an evolving host response to respiratory viral infection. Using clinical data, we show that societal suppression of respiratory virus transmission during coronavirus disease 2019 lockdown disrupted the traditional age gradient in pediatric asthma exacerbations, connecting the phenomenon of asthma remission to virus exposure. In mice, we show that asthmatic lung pathology triggered by Sendai virus (SeV) or influenza A virus is highly age-sensitive: robust in juvenile mice (4–6 wk old) but attenuated in mature mice (&gt;3 mo old). Interestingly, allergen induction of the same asthmatic traits was less dependent on chronological age than viruses. Age-specific responses to SeV included a juvenile bias toward type 2 airway inflammation that emerged early in infection, whereas mature mice exhibited a more restricted bronchiolar distribution of infection that produced a distinct type 2 low inflammatory cytokine profile. In the basal state, aging produced changes to lung leukocyte burden, including the number and transcriptional landscape of alveolar macrophages (AMs). Importantly, depleting AMs in mature mice restored post-SeV pathology to juvenile levels. Thus, aging influences chronic outcomes of respiratory viral infection through regulation of the AM compartment and type 2 inflammatory responses to viruses. Our data provide insight into how asthma remission might develop in children.

Asthma is a common chronic disease of childhood, but for unknown reasons disease activity sometimes subsides as children mature. To understand why, we exposed mice across a range of ages to viral and allergic triggers of asthma exacerbations and airway pathology. We found that pathology induced by Sendai virus (SeV) or influenza A virus (IAV) occurred selectively in juvenile mice in a microbiome-independent manner, while the same phenotypes induced by allergens were insensitive to age. Age-specific responses to SeV included a juvenile bias towards type-2 airway inflammation that emerged early in infection and was lost with maturation. With aging, we observed progressive transcriptional changes to alveolar macrophages (AMs) including the acquisition of high-level MHC-II expression. Importantly, depleting AMs canceled the protective effects of maturity on post-viral airway pathology. Thus, aging of the lung-immune microenvironment influences chronic outcomes of respiratory viral infection and may help to explain childhood asthma remission.

Importance Circadian rhythms affect fundamental immune processes, but how this translates to clinical outcomes like real-world vaccine effectiveness is unclear. Objective To examine associations between Coronavirus Infectious Disease 2019 (COVID-19) vaccination timing and effectiveness. Design, Setting, and Participants Retrospective cohort study of database records from Maccabi Healthcare Services (MHS), a major Israeli Health Maintenance Organization (HMO). We included all individuals over 12 with at least one timestamped vaccine dose and no documented COVID-19 infection prior to completing the initial 2-dose immunization series (n=1,515,754, 99.2% receiving BNT162b2). Database records spanned December 19, 2020, to April 25, 2022, encompassing two spikes in COVID infection dominated by the delta (B.1.617.2) and omicron (B.1.1.529) SARS-CoV-2 variants. Main Outcomes and Measures Outcomes included COVID-19 breakthrough infection and COVID-19 associated emergency department (ED) visits. Our main comparison was between patients vaccinated exclusively during morning hours (8:00-11:59), afternoon (12:00-15:59), or evening hours (16:00-19:59). We employed Cox multivariate regression to adjust for differences in age, sex, and co-morbidities. Results. Breakthrough infections differed based on vaccination time, with lowest rates associated with late morning to early afternoon, and highest rates with evening vaccination. Vaccination timing remained significant after adjustment for patient age, sex, and co-morbidities (HR=0.88 afternoon vs. evening, [95% CI 0.87-0.90]). Results were consistent in patients who received the basic two-dose vaccine series and who received booster doses. The association between COVID immunization time and infection risk followed a sinusoidal pattern, consistent with a biological rhythm in vaccine effectiveness that modifies clinical effectiveness by 8.6-25% depending on the vaccine dose (initial vaccine series, first booster, or second booster). The benefits of daytime vaccination were concentrated in younger and elderly patients. In contrast to breakthrough infections, COVID-19 related ED visits correlated with age and medical comorbidities but not with time of vaccination. Conclusions and Relevance We report a significant association between the time of COVID-19 vaccination and its clinical effectiveness in terms of breakthrough infection. These data have implications for mass vaccination programs.