Preadipocyte apoptosis is prevented by macrophage-conditioned medium in a PDGF-dependent manner

Abstract

Molgat AS, Gagnon A, Sorisky A. Preadipocyte apoptosis is prevented by macrophage-conditioned medium in a PDGF-dependent manner. Am J Physiol Cell Physiol 296: C757-C765, 2009. First published February 18, 2009 doi:10.1152/ajpcell.00617.2008.-Obesity is associated with macrophage accumulation and inflammation in adipose tissue. Macrophage-secreted factors have been reported to inhibit the differentiation of preadipocytes into adipocytes and to modulate adipogenic extracellular matrix gene expression. To enlarge our understanding of macrophages and the scope of their interactions with preadipocytes, we investigated their effect on preadipocyte survival. Acute exposure of 3T3-L1 preadipocytes to J774A.1 macrophage-conditioned medium (MacCM) stimulated platelet-derived growth factor receptor (PDGFR) tyrosine phosphorylation by 4.1-fold. There were significant increases in the phosphocontent of downstream PDGFR targets Akt and ERK1/2 (5.3-fold and 2.4-fold, respectively) that were inhibited by PDGF immunoneutralization or by the selective PDGFR inhibitor imatinib. Serum-free J774A.1-MacCM or RAW264.7-MacCM completely prevented 3T3-L1 preadipocyte apoptosis normally induced by serum deprivation. Addition of PDGF alone to serum-free control medium was sufficient to prevent 3T3-L1 preadipocyte apoptosis. Inhibition of PDGFR activation by MacCM, either by addition of imatinib or by PDGF immunodepletion of MacCM, effectively disrupted the prosurvival effect. In summary, our data indicate that MacCM promotes preadipocyte survival in a PDGFdependent manner.platelet-derived growth factor; obesity; macrophage OBESITY, defined as an increase in adiposity, results from a chronic positive energy balance. Expansion of adipose tissue occurs through the formation of new adipocytes, via the differentiation of stromal precursor preadipocytes, and the enlargement of existing adipocytes (9). Deficiency in the number of preadipocytes, or their capacity to differentiate, may lead to excessively hypertrophied and dysfunctional adipocytes that overproduce immune cell chemoattractant proteins (7,13,14). Concomitantly, the population of adipose tissue macrophages rises due to monocyte infiltration. This abnormal cellular remodeling of adipose tissue is associated with low-grade inflammation and insulin resistance (38,39).Paracrine communication among macrophages, adipocytes, and preadipocytes is believed to contribute to obesity-associated adipose tissue dysfunction (12). We and others have reported that macrophages produce anti-adipogenic factors that restrain the differentiation of preadipocytes into adipocytes (4,5,15,17,33,40). Macrophage-secreted factors have also been observed to have variable effects on preadipocyte proliferation (17,23). Apoptosis, the other key preadipocyte fate pertinent to adipose tissue remodeling (11, 21, 28), has not been evaluated with respect to potential macrophage paracrine interactions.The precise identity of the macrophage products influencing preadipocyte responses is not known. Here, we demonstrate th...

An inflammatory micro-environment promotes human adipocyte apoptosis

“…This resistance to apoptosis stimuli has also been shown for primary human preadipocytes and adipocytes (Fischer-Posovszky et al, 2004). We suggest that 3T3-L1 cells benefit from macrophagesecreted factors such as PDGF (Molgat et al, 2009) which are known to rescue cells from apoptosis. In M a n u s c r i p t 15 addition, it has been shown that macrophage media stimulate Akt phosphorylation in 3T3-L1 cells (Molgat et al, 2011), further supporting the differences between murine and human cells.…”

The activation state of macrophages alters their ability to suppress preadipocyte apoptosis

“…We have studied another cell fate, survival, and have previously reported that MacCM from J774A.1 macrophages protects 3T3-L1 preadipocytes from apoptosis in a PDGF-dependent manner, measured by cell enumeration, Hoechst staining, and annexin V detection by flow cytometry (Molgat et al 2009. Here, we report that pro-inflammatory macrophage activation reduces the pro-survival activity of J774A.…”

“…We previously reported that J774A.1-MacCM, in a PDGFdependent manner, inhibits apoptosis of serum-deprived 3T3-L1 preadipocytes, and this was documented by cell enumeration, Hoechst staining, and annexin V detection by flow cytometry (Molgat et al 2009. We have now investigated, for the first time, the effect of pro-inflammatory macrophage activation, induced by LPS treatment, on the preadipocyte survival activity of MacCM.…”

“…Shorter durations of LPS treatment were less effective. To investigate the mechanism by which LPS reduces the pro-survival activity of MacCM, we measured the amount of PDGF released into J774A.1-MacCM, as its ability to suppress preadipocyte apoptosis is dependent on this growth factor (Molgat et al 2009). RT-PCR comparative cycle number analysis indicated that PDGFB mRNA is 19-fold more abundant than PDGFA in unactivated macrophages (data not shown), which is in agreement with other observations (Nagaoka et al 1992).…”

“…Our previous investigations on macrophage-adipose cell interactions revealed that MacCM, collected under basal conditions, protects 3T3-L1 preadipocytes from apoptosis in a platelet-derived growth factor (PDGF)-dependent manner (Molgat et al 2009. Pro-inflammatory environments, induced by a high-fat diet, or cytokines, such as interleukin 6 (IL6), IL1b, and tumor necrosis factor a (TNFa), have been associated with adipose cell death, both in vitro and in vivo (Niesler et al 2000, Tchkonia et al 2005, Alkhouri et al 2010.…”