Effects of the nerve growth factor and its carrier protein on the inflammatory response from human monocytes

BackgroundThe nerve growth factor (NGF) has been previously shown to be involved in cellular proliferation, differentiation, survival, or wound healing. This factor displays a variety of biological effects that yet remain to be explored. Previous data on cell lines show a pro-inflammatory role of NGF on monocytes.ObjectivesThe objective of the study was to investigate the pro-inflammatory effect of NGF, using a model of fresh human monocytes.MethodsMonocytes obtained from PBMC were exposed to NGF at various concentrations. Alternatively, monocytes were exposed to BSA, the NGF carrier protein without the NGF. Gene expression and cytokine release in the supernatant were monitored.ResultsWe found that NGF increased the expression of pro-inflammatory, chemotactic, and remodeling genes such as interleukin (IL)-1 beta, IL-6, tumor necrosis factor (TNF)-alpha, and C-X-C motif ligand (CXCL)8. The protein levels of CXCL8 and matrix metalloproteinase (MMP)-9 were also increased in the cell supernatants following NGF exposure. BSA alone was found to drive part of this response, bringing nuance to the inflammatory potential of the NGF.ConclusionThese data suggest that NGF is able to enhance monocyte inflammatory responses once cells are stimulated with another signal but is possibly not able to directly activate it. This could have implications for example in patients with bacterial infections, where NGF could worsen the local inflammation by over-activating immune cells.