Influence of Glucose Concentration on Macrophage Polarization in vitro

Abstract

The innate immune response represents a critical piece of overall immunity, driving the immediate reaction to a variety of conserved antigens which are known to cause a multitude of diseases. Central to the innate response are macrophages, a heterogeneous population of monocyte derived immune cells capable of both killing bacteria directly as well as orchestrating a more complex innate and adaptive immune response. Indeed, macrophages provide both inflammatory responses to rid the body of bacteria while also helping to control inflammatory responses through the production of immune regulators such as interleukin 10 and transforming growth factor beta. Growing evidence indicates that environmental factors may influence this balance of inflammatory, or M1 macrophages, and regulator, or M2 macrophages. Intriguingly, the macronutrient fuel source itself powering the macrophage may influence its polarization dynamics. This study will evaluate the impact of glucose concentration on the in vitro polarization of murine macrophages. Given that hyperglycemia is associated, in humans, with chronic low-grade inflammation, it is hypothesized that macrophages cultured in high glucose conditions will present with increased M1 macrophage marker production (e.g. tumor necrosis factor alpha, TNFa; macrophage chemotactic protein 1, MCP-1; inducible nitric oxide synthase, iNOS) upon activation with inflammatory stimuli (lipopolysaccharide, LPS) and suppressed M2 (anti-inflammatory) responses following treatment with interleukin 4 (IL4) including decreased mannose receptor expression, interleukin 10 (IL10),and transforming growth factor beta (TGFb) expression. To this end, murine macrophages were cultured in either normal glucose (100 mg/dL) or high glucose (450 mg/dL) in the presence or absence of M1 or M2 activating stimuli (LPS/IFNg or IL4 respectively). Following 3hr of exposure to stimuli, cells were harvested and RNA isolated for quantitative PCR analysis. High glucose conditions enhanced the expression of TNFa and iNOS in response to M1 stimuli when compared to normal glucose conditions. M2 responses were impaired in the high glucose group when compared to normal-glucose conditions as assessed by gene expression for Arginase I and IL10. High glucose alone appears capable of altering macrophage responses, augmenting standard inflammatory reactions to conserved stimuli like LPS while also impairing regulatory, or M2 macrophage development. Therapeutics aimed at limiting M1 responses may prove useful in treating or preventing chronic health conditions associated with diabetes among other disease states.