Short chain fatty acids may elicit an innate immune response from preadipocytes: a potential link between bacterial infection and inflammatory diseases.

Short chain fatty acids (SCFAs) such as acetate, propionate and butyrate are produced by bacterial fermentation of dietary fiber. The highest concentrations of SCFAs in the body are found in the colon. Elevated dietary acetate has been shown to have anti-inflammatory effects in mouse models of colitis and inflammatory diseases in peripheral tissues. The details of how dietary SCFAs stimulate reduced inflammation in peripheral tissues have not been determined. I suggest that SCFA concentrations in peripheral tissues are generally not sufficient to locally produce a significant anti-inflammatory effect from immune cells. Moreover it is possible that elevated SCFA levels in peripheral tissues may actually stimulate an inflammatory response. The hypothesis is presented that preadipocytes and other cells with immune function such as fibroblasts in peripheral tissues elicit an inflammatory innate immune response when exposed to SCFAs at millimolar concentrations. A role for SCFAs in activating an immune response in preadipocytes is possible given the expression of a SCFA receptor in these cells, the demonstration that adipocytes and preadipocytes have immunity related functions, the observation that 2mM SCFAs stimulated the expression of monocyte chemoattractant protein-1 (MCP-1) mRNA from 3T3-L1 preadipocytes and that concentrations of SCFAs can reach elevated levels at sites of bacterial infection. A SCFA-induced inflammatory response from preadipocytes and other cells with immune function, such as fibroblasts, may provide a further contributing factor linking bacterial infection to the development of insulin resistance and the severity of inflammatory diseases such as atherosclerosis.