Abstract Body (Do not enter title and authors here): Introduction: Viral respiratory infections (VRIs) are linked to cardiovascular complications that are more severe in the elderly, yet mechanistic understanding and therapeutic strategies remain limited.
Hypothesis: We hypothesized that aging impairs lymphatic function, thereby exacerbating cardiac dysfunction following chronic influenza infection.
Methods: We evaluated cardiac function (exercise capacity testing and echocardiography), lymphatic function (in vivo fluorescence imaging, fluorescent staining, and H&E staining) and immune infiltration (flow cytometry and histology) in young and aged mice infected with H1N1 (PR8) virus. Organelle changes in lymphatic endothelial cells (LECs) from young (P3) and aged (P9) cells were analyzed via cell painting and tube formation assays.
Results: Aged mice infected with H1N1 exhibited markedly worsened cardiac dysfunction compared to age-matched controls, including reduced exercise capacity (p = 0.003) and diastolic dysfunction (E/A, p < 0.001), while no changes were observed in young H1N1 mice. Lymphatic phenotype revealed severely impaired lymphatic drainage in aged H1N1 mice, whereas young H1N1 mice showed enhanced lymphatic function. Myocardial edema (H&E staining, p < 0.05) and increased left ventricular posterior wall thickness (LVPWD; p = 0.002) were also observed in aged H1N1 mice. Immunohistochemistry showed substantially increased myocardial CD3+ accumulation in aged H1N1 mice (p = 0.001), with no notable changes in young mice. Flow cytometry revealed increased accumulation of double-negative T cells and B cells in aged H1N1 hearts vs. aged controls (p < 0.03), but no changes in young hearts. P21 was upregulated in aged H1N1 hearts (p < 0.03). In vitro, aged LECs in response to H1N1 plasma exhibited reduced endoplasmic reticulum (ER) and mitochondrial density (p < 0.0001 for both). Treatment with a p21 inhibitor (UC2288) or VEGFC protein restored both ER and mitochondrial defects (p < 0.0001 for both) in aged H1N1 LECs. The p21 inhibitor also enhanced tube formation capacity in aged H1N1 LECs (p = 0.016). 8-week treadmill training (5 days/week, 45 min/day, 10 m/min) in aged H1N1 mice significantly improved exercise capacity, preserved cardiac function, and enhanced survival (75% vs. 42.86%) compared to age-matched controls.
Conclusion: Aging-associated lymphatic dysfunction, immune remodeling, and endothelial senescence are key mechanisms driving severe cardiac complications following chronic H1N1 infection.