Regulation of activin A release from murine bone marrow-derived neutrophil precursors by tumour necrosis factor-α and insulin

Activin A, a transforming growth factor-β family cytokine, plays a crucial role in regulating the onset and severity of many inflammatory conditions, such as acute lipopolysaccharide (LPS)-induced inflammation. Activin A is also implicated in type 2 diabetes (T2D), a disease characterised by insulin resistance, hyperglycaemia and chronic elevation of pro-inflammatory cytokines, including tumour necrosis factor (TNF-α). In the human, neutrophils contain activin A that can be released in response to TNF-α. Studies of inflammatory disease in vivo, however, generally use the mouse, so it is essential to know if murine neutrophils have similar properties. Regulation of activin A was investigated in bone marrow-derived neutrophil precursors (BMNPs) from 8 to 10 weeks old C57BL6/J male mice. The BMNPs contained 7-fold higher concentrations of activin A than bone marrow mononuclear cells. Release of activin A from isolated BMNPs was stimulated by TNF-α, but this was not due to increased activin A production. In contrast to TNF-α, LPS had no effect on isolated BMNPs, but stimulated activin A release and production in total bone marrow cell cultures. Moreover, activin A release in response to LPS, was not prevented in TNF-α null mice. Increased glucose and insulin had no effect on base-line activin A secretion by BMNPs in culture, but pre-treatment with insulin blocked the TNF-α induced release of activin A. These results indicate that murine neutrophils are a source of stored activin A, the release of which can be directly stimulated by TNF-α, although TNF-α is not the only stimulator of activin A release during inflammation. Furthermore, regulation of neutrophil activin A release by insulin may also play a role in the inflammation associated with T2D.