Coupling In silico and In vitro Mechanistic Models to Define Vitamin D3 Immunomodulation of IL-12 and Nitric Oxide in Mycobacterium tuberculosis Infection.

Tuberculosis, caused by Mycobacterium tuberculosis (Mtb), is a highly infectious disease mainly affecting the lungs. Macrophages are key phagocytic immune cells and the preferred hosts for intracellular bacteria growth. Macrophages are also important sites of vitamin D3 synthesis, with vitamin D3 deficiency associated with increased risk of developing active TB. There is great interest in vitamin D3 as adjunctive therapy due to its immunomodulatory and antimicrobial properties, particularly the effect on proinflammatory effectors like bactericidal nitric oxide (NO). NO production requires inducible nitric oxide synthase expression, which is regulated by IFN-γ, a pro-inflammatory cytokine upregulated by IL-12. Vitamin D3 serves an important host protective function to regulate NO production to a level that is sufficient to restrict Mtb growth while avoiding uncontrolled inflammation. While previous in vitro studies have shown that vitamin D3 modulates NO levels and IL-12, in an infection dose-dependent manner, to date, there are no computational models that capture the mechanisms by which vitamin D3 regulates NO production during high and low Mtb infection. Using an integrative systems biology approach, we define key signaling pathways involved in vitamin D3 immunometabolism and determine the impact of vitamin D3 sufficiency/deficiency given infection dosage. Data from multiple computational models and in vitro infection studies are integrated into a mechanistic model, and simulation results compared to in vitro IL-12 and NO concentrations from our in vitro models of infection. Concurrence between our in-silico and in vitro models demonstrates the feasibility of NO modulation in a vitamin D3 and infection level dependent manner.