NGF gene expression and secretion by canine adipocytes in primary culture: upregulation by the inflammatory mediators LPS and TNFalpha.

Obesity is the commonest nutritional disorder of companion animals. In rodents and humans, white adipose tissue is a major endocrine and secretory organ, releasing adipokines linked to inflammation. In this study, we examined whether nerve growth factor (NGF), a target-derived neurotrophin central to the development/maintenance of sympathetic innervation and an inflammatory response protein, is synthesized and secreted by canine adipocytes. NGF mRNA was detected in each of the major fat depots (the subcutaneous, inguinal, gonadal, perirenal, and falciform ligaments) of dogs at similar levels. Canine adipocytes, differentiated from preadipocytes (inguinal depot) in primary culture, expressed the NGF gene and secreted NGF both pre- and post-differentiation. Treatment of the differentiated adipocytes with LPS resulted in a dramatic increase in NGF mRNA levels (20-fold at 24 h) and in NGF protein in the medium (60-fold at 24 h). The proinflammatory cytokine TNFalpha also led to a substantial increase in NGF mRNA levels (11-fold) and protein secretion (16-fold), while IL-6 had little effect. In contrast, dexamethasone decreased both NGF mRNA levels (80%) and protein release (60%). The PPARgamma agonist rosiglitazone also reduced NGF secretion. These results demonstrate that canine white adipocytes synthesize and secrete NGF, the powerful upregulation by LPS and TNFalpha indicating that the neurotrophin is strongly linked to the inflammatory response in canine WAT. Canine adipocytes appear highly sensitive to inflammatory stimuli.