Activation of skeletal muscle FAPs by LPA requires the Hippo signaling via the FAK pathway

by Selleckchem | Aug 11 2023

Lysophosphatidic acid (LPA) is a lysophospholipid that signals through six G-protein coupled receptors (LPARs), LPA1 to LPA6. LPA has been described as a potent modulator of fibrosis in different pathologies. In skeletal muscle, LPA increases fibrosis-related proteins and the number of fibro/adipogenic progenitors (FAPs). FAPs are the primary source of ECM-secreting myofibroblasts in acute and chronic damage. However, the effect of LPA on FAPs activation in vitro has not been explored. This study aimed to investigate FAPs' response to LPA and the downstream signaling mediators involved. Here, we demonstrated that LPA mediates FAPs activation by increasing their proliferation, expression of myofibroblasts markers, and upregulation of fibrosis-related proteins. Pretreatment with the LPA1/LPA3 antagonist Ki16425 or genetic deletion of LPA1 attenuated the LPA-induced FAPs activation, resulting in decreased expression of cyclin e1, α-SMA, and fibronectin. We also evaluated the activation of the focal adhesion kinase (FAK) in response to LPA. Our results showed that LPA induces FAK phosphorylation in FAPs. Treatment with the P-FAK inhibitor PF-228 partially prevented the induction of cell responses involved in FAPs activation, suggesting that this pathway mediates LPA signaling. FAK activation controls downstream cell signaling within the cytoplasm, such as the Hippo pathway. LPA induced the dephosphorylation of the transcriptional coactivator YAP (Yes-associated protein) and promoted direct expression of target pathway genes such as Ctgf/Ccn2 and Ccn1. The blockage of YAP transcriptional activity with Super-TDU further confirmed the role of YAP in LPA-induced FAPs activation. Finally, we demonstrated that FAK is required for LPA-dependent YAP dephosphorylation and the induction of Hippo pathway target genes. In conclusion, LPA signals through LPA1 to regulate FAPs activation by activating FAK to control the Hippo pathway.

Comments:

Lysophosphatidic acid (LPA) is a type of lysophospholipid that can signal through six G-protein coupled receptors (LPARs) known as LPA1 to LPA6. LPA has been shown to play a significant role in modulating fibrosis in various pathologies. Specifically, in skeletal muscle, LPA has been found to increase the expression of fibrosis-related proteins and promote the proliferation of fibro/adipogenic progenitors (FAPs). FAPs are a key source of myofibroblasts, which are involved in the deposition of extracellular matrix (ECM) during acute and chronic muscle damage. However, the specific effect of LPA on FAP activation in vitro has not been thoroughly investigated.

The aim of this study was to examine how FAPs respond to LPA and identify the signaling pathways involved in this activation process. The researchers demonstrated that LPA is capable of mediating FAP activation by enhancing their proliferation, increasing the expression of myofibroblast markers, and upregulating fibrosis-related proteins. They found that pre-treatment with the LPA1/LPA3 antagonist Ki16425 or genetic deletion of LPA1 attenuated the activation of FAPs induced by LPA. As a result, the expression of cyclin e1, α-SMA, and fibronectin, which are markers associated with FAP activation and fibrosis, were decreased.

The study also investigated the activation of focal adhesion kinase (FAK) in response to LPA. The results revealed that LPA triggers the phosphorylation of FAK in FAPs. Treatment with the P-FAK inhibitor PF-228 partially prevented the induction of cellular responses associated with FAP activation, indicating that FAK is involved in mediating LPA signaling. FAK activation plays a role in downstream cellular signaling within the cytoplasm, including the Hippo pathway.

Furthermore, the researchers observed that LPA induces the dephosphorylation of the transcriptional coactivator YAP (Yes-associated protein) in FAPs. This dephosphorylation event leads to the direct expression of target genes associated with the Hippo pathway, such as Ctgf/Ccn2 and Ccn1. The inhibition of YAP's transcriptional activity with Super-TDU further confirmed the involvement of YAP in LPA-induced FAP activation. Finally, the study demonstrated that FAK is necessary for LPA-dependent YAP dephosphorylation and the induction of Hippo pathway target genes.

In summary, LPA signals through LPA1 to regulate the activation of FAPs by activating FAK, which, in turn, controls the Hippo pathway. These findings provide insights into the mechanisms underlying LPA-induced fibrosis and identify potential targets for therapeutic interventions aimed at mitigating fibrotic processes in skeletal muscle and potentially other pathologies.