Macrophage-Specific Progranulin Deficiency Prevents Diet-Induced Obesity through the Inhibition of Hypothalamic and Adipose Tissue Inflammation.

Background: Chronic low-grade inflammation in multiple metabolic organs contributes to the development of insulin resistance induced by obesity. Progranulin (PGRN) is an evolutionarily-conserved secretory protein implicated in immune modulation. The generalized deletion of the PGRN-encoded Grn gene improves insulin resistance and glucose intolerance in obese mice fed a high-fat diet (HFD). However, it remains unclear which cells or organs are responsible for the beneficial metabolic effect of Grn depletion.

Methods: Considering the critical role of macrophages in HFD-induced obesity and inflammation, we generated mice with a macrophage-specific Grn depletion (Grn-MΦKO mice) by mating lysozyme M (LysM)-Cre and Grn-floxed mice. Body weight, food intake, energy expenditure, and glucose and insulin tolerance were compared between Grn-MΦKO mice and their wildtype (WT) controls under normal chow diet (NCD)- or HFD-fed conditions. We also examined macrophage activation and inflammation- related gene expression in the visceral adipose tissue and hypothalamus along with insulin and leptin signaling.

Results: Grn-MΦKO mice showed no alteration in metabolic phenotypes under NCD-fed conditions. However, upon HFD feeding, these mice exhibited less weight gain and improved glucose and insulin tolerance compared to WT mice. Moreover, HFD-induced macrophage activation and proinflammatory cytokine expression were significantly reduced in both the adipose tissue and hypothalamus of Grn-MΦKO mice, while HFD-induced impairments in leptin and insulin signaling showed improvement.

Conclusion: Macrophage-derived PGRN and possibly other Grn products play a critical role in the development of HFD-induced obesity, tissue inflammation, and impaired hormonal signaling in both central and peripheral metabolic organs.