Composition of fatty acids in a high‐fat diet affects adipose tissue inflammation by inducing calreticulin on adipocytes and activating group 1 innate lymphoid cells

Obesity‐induced adipose tissue inflammation plays a critical role in the development of metabolic diseases. For example, NK1.1+ group 1 innate lymphoid cells (G1‐ILCs) in adipose tissues are activated in the early stages of inflammation in response to a high‐fat diet (HFD). In this study, we examined whether the composition of fatty acids affected adipose inflammatory responses induced by an HFD. Mice were fed a stearic acid (C18:0)‐rich HFD (HFD‐S) or a linoleic acid (C18:2)‐rich HFD (HFD‐L). HFD‐L‐fed mice showed significant obesity compared with HFD‐S‐fed mice. Visceral and subcutaneous fat pads were enlarged and contained more NK1.1+KLRG1+ cells, indicating that G1‐ILCs were activated in HFD‐L‐fed mice. We examined early changes in adipose tissues during the first week of HFD intake, and found that mice fed HFD‐L showed increased levels of NK1.1+CD11b+KLRG1+ cells in adipose tissues. In adipose tissue culture, addition of 4‐hydroxynonenal, the most frequent product of lipid peroxidation derived from unsaturated fatty acids, induced NK1.1+CD11b+CD27− cells. We found that calreticulin, a ligand for the NK activating receptor, was induced on the surface of adipocytes after exposure to 4‐hydroxynonenal or a 1‐week feeding with HFD‐L. Thus, excess fatty acid intake and the activation of G1‐ILCs initiate and/or modify adipose inflammation. Calreticulin, a ligand for the NK activating receptor, is induced on the surface of adipocytes after exposure to 4‐hydrocynonenal (HNE) or short feeding with linoleic acid‐rich high‐fat diet (HFD). Calreticulin on adipocytes activates G1‐ILCs in fat tissue, induces IFN‐gamma production and modifies adipose inflammation.