Obesity is associated with an activated macrophage phenotype in multiple tissues that contributes to tissue inflammation and metabolic disease. To evaluate the mechanisms by which obesity potentiates myeloid activation, we evaluated the hypothesis that obesity activates myeloid cell production from bone marrow progenitors to potentiate inflammatory responses in metabolic tissues. High fat diet-induced obesity generated both quantitative increases in myeloid progenitors as well as a potentiation of inflammation in macrophages derived from these progenitors. In vivo, hematopoietic stem cells from obese mice demonstrated the sustained capacity to preferentially generate inflammatory CD11c+ adipose tissue macrophages after serial bone marrow transplantation. We identified that hematopoietic MyD88 was important for the accumulation of CD11c+ adipose tissue macrophage accumulation by regulating the generation of myeloid progenitors from HSCs. These findings demonstrate that obesity and metabolic signals potentiate leukocyte production and that dietary priming of hematopoietic progenitors contributes to adipose tissue inflammation.

Background: Diet-induced obesity leads to a chronic low grade inflammation with production of activated macrophages associated with systemic sexually dimorphic metabolic dysfunction. Results: Males have enhanced myelopoiesis and a proinflammatory response to obesity compared with females. Conclusion: Sex differences in myelopoiesis result in dimorphic responses to obesity-induced inflammation. Significance: Given differences in inflammatory responses, targeted treatment strategies are probably required for males and females.

While there was no difference in in-hospital mortality by obesity diagnosis, variation in organ dysfunction, hospital stay, and hospital charges according to obesity status was mediated by illness severity. Findings from this study have significant implications for targeted approaches to mitigate the burden of obesity on infection and sepsis.

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