FSTL1 is an antagonist of ERK1/2 phosphorylation during ciliogenesis and preadipocyte differentiation.

FSTL1 is a secreted glycoprotein that is involved in several processes in health and disease, including development, cardiovascular disease, cancer, inflammation, and obesity. The signaling pathways used by FSTL1 to act on target tissues seem to activate different intracellular mediators specific to each tissue and several of the mechanisms of action remain to be determined at the molecular level, including intracellular mediators and receptors. We have previously unveiled a novel role for FSTL1 in ciliogenesis and provided evidence for an Fstl1/cilia axis in preadipocyte differentiation. This pathway is relevant to the pathogenesis of obesity and of a group of conditions called ciliopathies since they are caused by the dysfunction of the primary cilia. This work aimed to identify intracellular mediators of FSTL1 action on ciliogenesis and adipogenesis. We analyzed ERK phosphorylation levels as well as cilia length in the absence of FSTL1 and in the presence of the pERK inhibitor U0126. We also analyzed the differentiation and cilia dynamics of U0126-treated preadipocytes and tested the ERK-mediated signaling by BMP4 in the presence of added extracellular Fstl1. Here, we propose that MAP kinase ERK is a mediator of ciliogenesis downstream of FSTL1 and provide additional data that suggest that FSTL1 antagonizes BMP non-canonical signaling to modulate ciliogenesis and adipogenesis. In sum, our data reinforce the interest on the axis FSTL1/cilia in the modulation of adipogenesis and provide evidence to add ERK to this working model.