Patient-specific premorbidity, age, and sex are significant heterogeneous factors that influence the severe manifestation of
lung diseases, including
COVID-19 fibrosis. The renin-angiotensin system (RAS) plays a prominent role in regulating effects of these factors. Recent evidence suggests that patient-specific alteration of RAS homeostasis with premorbidity and the expression level of
angiotensin converting enzyme 2 (ACE2), depending on age and sex, is correlated with lung
fibrosis. However, conflicting evidence suggests decreases, increases, or no changes in RAS after
SARS-CoV-2 infection. In addition, detailed mechanisms connecting the patient-specific conditions before
infection to
infection-induced
fibrosis are still unknown. Here, a mathematical model is developed to quantify the systemic contribution of heterogeneous factors of RAS in the progression of lung
fibrosis. Three submodels are connected-a RAS model, an agent-based
COVID-19 in-host immune response model, and a
fibrosis model-to investigate the effects of patient-group-specific factors in the systemic alteration of RAS and
collagen deposition in the lung. The model results indicate cell death due to inflammatory response as a major contributor to the reduction of ACE and ACE2, whereas there are no significant changes in ACE2 dynamics due to viral-bound internalization of ACE2. Reduction of ACE reduces the homeostasis of RAS including
angiotensin II (ANGII), while the decrease in ACE2 increases ANGII and results in severe
lung injury and
fibrosis. The model explains possible mechanisms for conflicting evidence of RAS alterations in previously published studies. Also, the results show that ACE2 variations with age and sex significantly alter RAS
peptides and lead to
fibrosis with around 20% additional
collagen deposition from systemic RAS with slight variations depending on age and sex. This model may find further applications in patient-specific calibrations of tissue models for acute and chronic
lung diseases to develop personalized treatments.