Altered macrophage population and phenotype in mesenteric perivascular adipose tissue during inflammatory bowel disease pathogenesis
Authors: Ramos Kassandra , Ramos Kassandra , Jenkins Sam , Grunz Elizabeth , Boerman Erika 
Published: May 2023

Objective: Inflammatory bowel diseases (IBD) are characterized by chronic intestinal inflammation and aberrant immune responses that are linked to decreased intestinal blood flow and adipose hyperplasia around the intestines. Perivascular adipose tissue (PVAT) contains a dynamic macrophage population and acts as a key regulator of arterial blood flow and inflammation. Preliminary studies found that PVAT surrounding mesenteric arteries shifts from anti-contractile to pro-contractile in established IBD, but whether PVAT macrophage content and/or phenotype distribution changes during IBD development remains unclear. Therefore, we tested the hypothesis that IBD pathogenesis is associated with a persistent increase in proinflammatory M1-like macrophages and a simultaneous decrease in anti-inflammatory M2-like macrophages. Methods: Male and female IL10-/- mice were gavaged with H. hepaticus at weaning and developed IBD for 1, 5, 10, 20, 40, 80, 160 or 240 days, with days 80-240 encompassing the 15-30 year age range most common for human IBD diagnosis. Age-matched C57BL/6 mice served as controls, and non-gavaged Day 0 mice were included in each group. PVAT surrounding mesenteric arteries was fixed and immunolabeled for total macrophages (MT, F4/80), M1-like macrophages (M1, CD68) and M2-like macrophages (M2, CD206). PVAT samples were confocally imaged, with fluorescence area and M2:M1 area ratio quantified from max z-projections. Differences within timepoints were analyzed by nested one-way ANOVA, and differences across timepoints were compared via two-way ANOVA. Results: PVAT MTs (F4/80+) were elevated in IBD vs Control at all timepoints (P<0.05). In Controls, MTs increased from Day 0-20 then plateaued through Days 240. In contrast, MTs from IBD mice decreased from Days 1-10 then steadily increased to Day 240. M1s (CD68+) increased in IBD vs Control at all timepoints (P<0.05). While M1 levels persisted across timepoints in Controls, IBD M1s decreased through Day 20 then steadily rose through Day 240. M2s (CD206+) increased from Day 0-20 in Controls, then plateaued through Day 240. The opposite occurred in IBD: decreased M2s through Day 80 that persist through Day 240. The M2:M1 ratio over time highlights key differences in Control vs IBD PVAT. The M2:M1 ratio is greater in Control vs IBD at all timepoints, and the magnitude of difference increases over time (P<0.05). While the M2:M1 ratio increases over time in Controls, it decreases over time in IBD. Overall, timepoint-specific differences varied, but there was a main effect of both disease and time for MTs, M1s, M2s and M2:M1 ratio. Conclusion: IBD pathogenesis is associated with early and persistent increases in total and M1 macrophages but decreases M2 macrophages and M2:M1 ratio. These data suggest that (1) PVAT inflammation precedes intestinal inflammation typically observed at 12-16 weeks and (2) PVAT macrophages may be an important driver of vascular dysfunction in IBD. Funding: T34 GM 136493 to KRR, R01HL157038, R00HL129196 to EMB. This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.