Helminth infection induces RELMa-dependent adipose tissue transcriptional reprogramming and protection against diet-induced obesity
Obesity, a rising epidemic in the United States, is causally associated with adipose tissue inflammation, therefore targeting this immune dysfunction offers promising therapeutic avenues. Chronic helminth infection can prevent obesity pathogenesis but there remain opportunities to determine the immune factors that mediate protection and whether long-term protection is associated with changes in the visceral adipose tissue. We optimized a mouse model of western diet-induced obesity and investigated if transient helminth infection was protective through the immunoregulatory protein RELM. Wild-type (WT) or RELM knockout (KO) C57BL/6J mice were fed a western diet of high glucose and high fat followed by infection with helminth Nippostrongylus brasiliensis, which infects the lung and small intestine but is cleared within two weeks. Infection attenuated weight gain and improved glucose tolerance even after the parasite was expelled in WT but not RELM deficient mice. This protection was associated with reduced adipocyte hypertrophy in WT mice. Adipose tissue bulk RNA sequencing and digital cell quantification indicated that RELM promoted enrichment of eosinophils and M2 macrophages and upregulated pathways associated with fatty acid oxidation, mitochondrial function, and thermogenesis, whereas RELM deficiency led to pro-inflammatory, fibrotic, and lipid accumulation transcriptional profiles. Specific genes that were changed with infection and RELM deficiency included collagen and serpin genes associated with tissue remodeling and fibrosis, and changes within the adipose tissue was confirmed by immunofluorescent staining. Together, these findings establish that helminth-induced RELM critically protects against western diet-driven obesity and associated adipose transcriptional reprogramming and tissue remodeling.