We showed previously in cultures of primary human adipocytes and preadipocytes that
lipopolysaccharide and
trans-10,cis-12-conjugated linoleic acid (10,12-CLA) activate the inflammatory signaling that promotes
insulin resistance. Because our published data demonstrated that preadipocytes are the primary instigators of inflammatory signaling in
lipopolysaccharide-treated cultures, we hypothesized that they played the same role in 10,12-CLA-mediated
inflammation. To test this hypothesis, we employed four distinct models. In model 1, a differentiation model, CLA activation of MAPK and induction of
interleukin-8 (IL-8),
IL-6, IL-1beta, and cyclo-oxygenase-2 (COX-2) were greatest in differentiated compared with undifferentiated cultures. In model 2, a cell separation model, the
mRNA levels of these inflammatory
proteins were increased by 10,12-CLA compared with
bovine serum albumin vehicle in the adipocyte fraction and the preadipocyte fraction. In model 3, a co-culture insert model, inserts containing approximately 50% adipocytes (AD50) or approximately 100% preadipocytes (AD0) were suspended over wells containing AD50 or AD0 cultures. 10,12-CLA-induced
IL-8,
IL-6, IL-1beta, and COX-2
mRNA levels were highest in AD50 cultures when co-cultured with AD0 inserts. In model 4, a
conditioned medium (CM) model, CM collected from CLA-treated AD50 but not AD0 cultures induced
IL-8 and
IL-6 mRNA levels and activated phosphorylation of MAPK in naive AD0 and AD50 cultures. Consistent with these data, 10,12-CLA-mediated secretions of
IL-8 and
IL-6 from AD50 cultures were higher than from AD0 cultures. Notably, blocking
adipocytokine secretion prevented the inflammatory capacity of CM from 10,12-CLA-treated cultures. These data suggest that CLA instigates the release of inflammatory signals from adipocytes that subsequently activate adjacent preadipocytes.