Human and mouse monocytes display distinct signalling and cytokine profiles upon stimulation with FFAR2/FFAR3 short-chain fatty acid receptor agonists.

Knockout mice studies implicate the mammalian short-chain fatty acid (SCFA) receptors, FFAR2 and FFAR3- in colitis, arthritis and asthma. However, the correlation with human biology is uncertain. Here, we detected FFAR2 and FFAR3 expression in human monocytes via immunohistochemistry. Upon treatment with acetate SCFA or FFAR2- and FFAR3-specific synthetic agonists, human monocytes displayed elevated p38 phosphorylation and attenuated C5, CCL1, CCL2, GM-CSF, IL-1α, IL-1β and ICAM-1 inflammatory cytokine expression. Acetate and FFAR2 agonist treatment also repressed Akt and ERK2 signalling. Surprisingly, mouse monocytes displayed a distinct response to acetate treatment, elevating GM-CSF, IL-1α, and IL-1β cytokine expression. This effect persisted in FFAR2/3-knockout mouse monocytes and was not reproduced by synthetic agonists, suggesting a FFAR2/3 independent mechanism in mice. Collectively, we show that SCFAs act via FFAR2/3 to modulate human monocyte inflammatory responses- a pathway that is absent in mouse monocytes.