Response to "Perivascular adipose tissue and inflammation

TO THE EDITOR: The authors thank Dr. Goodwill for his queries regarding the methods used in our paper, “Disconnect Between Adipose Tissue Inflammation and Cardiometabolic Dysfunction in Ossabaw Pigs. ” As other readers may have similar questions, we appreciate the opportunity to address these concerns. Dr. Goodwill correctly summarized our main findings, which were that Ossabaw swine fed a Western diet develop many cardiometabolic impairments, including insulin resistance and atherosclerotic disease, yet are apparently protected from adipose tissue inflammation (1). In response to his first concern regarding the validity of our ex vivo adipose tissue-conditioned media experiments, we agree that there are limitations to this tissue culture approach, and on their own, the conditioned media experiments should not be used to assess the inflammatory state of the tissue. However, those data, combined with the tissue data at gene and protein levels and circulating cytokines, support a lack of obesity-associated inflammation in this model. Nonetheless, more studies are needed before definitive conclusions can be drawn, especially regarding adipose tissue adipokine secretion. Regarding use of CD68 as a macrophage marker, we appreciate this comment, as the field of immunometabolism is only recently emerging, and it is crucial that the limitations and utility of specific markers, across models, are acknowledged. Our group has used this porcine-specific macrophage marker with paraffin embedded tissues from Ossabaw pigs previously (2). The point that CD68 staining intensity was reported to be lower in porcine compared to human tissue may not be relevant considering our study is comparing lean to obese pigs, and not pigs to humans. As any one marker has limitations, we chose to measure expression levels of several macrophage markers in addition to CD68 (e.g., F4/80, CD14, CD16, CD163), and we measured SRA-positive cells, an additional marker of macrophage content. Finally, Dr. Goodwill brings up the intriguing idea that CD163, although traditionally viewed as anti-inflammatory (3), may also have inflammatory actions. We agree with this possibility—indeed, CD163 was increased in the subcutaneous adipose tissue of obese pigs, and a few other more traditional inflammatory markers (e.g., IL-1) had a tendency to increase, although these differences are yet to reach statistical significance. These data may suggest at least modest inflammatory changes at the gene level. However, given that the vast majority of inflammatory markers were not elevated, or even reduced (e.g., IFN-c), despite significant adipose tissue hypertrophy, our data remain supportive of the contention that, in the Ossabaw model, adipose tissue inflammation is not a hallmark of cardiometabolic dysfunction. Certainly, more research is necessary to better understand the relationship between adipose tissue immunometabolism and cardiometabolic health in humans as well as relevant animal species. Importantly, we observed insulin resistance and other cardiometabolic impairments, yet no adipose or systemic inflammation. While this does not rule out the possibility that inflammation will develop later in these animals, it does not favor the hypothesis that adipose tissue inflammation is necessary for the initiation of cardiometabolic dysfunction, despite the body of literature showing a connection between adipose tissue inflammation, insulin resistance, and cardiovascular disease (4). O