Experimental Study Of IL-4-induced FABP4 Through Activating PPAR γ Signaling Pathway In Regulating Human Skeletal Muscle Cells Lipogenesis

Objective To investigate the role of Fatty acid binding protein 4（FABP4）/ Peroxisome proliferator-activated receptor-γ（PPAR γ）signaling pathway in regulating human skeletal muscle cells lipogenesis by establishing a cellular model of lipogenesis in vitro.Methods This study collected 30 cases of lumbar paravertebral muscle tissue from patients who underwent transforaminal lumbar interbody fusion at the Provincial Hospital Affiliated to Anhui Medical University from 2020.08 to 2020.10.According to the preoperative MRI to evaluate the degree of muscle lipid infiltration,15 cases of normal paraspinal muscle tissue and 15 cases of lipid infiltrated paraspinal muscle tissue were selected.The muscle tissues were subjected to Tandem mass spectrometry（TMT）to screen the differentially expressed proteins,and the signaling pathways related to the differential proteins were predicted through the Kyoto Encyclopedia of Genes and Genomes（KEGG）website.The muscle tissue specimens of the two groups were subjected to immunohistochemical staining of differential proteins to verify the results of TMT.Isolation,cultivating,morphological observation and identification of human normal skeletal muscle cells were conducted.A cellular model of lipogenesis in vitro of human skeletal muscle cells（HSMCs）was established.The expression of lipogenesisrelated indicators and pathway-related proteins in muscle cells was also detected.The key proteins inhibitors and pathway proteins inhibitors were added respectively to verify the role of key proteins and signaling pathways in the lipogenesis of muscle cells.Results The TMT results showed that FABP4 protein was highly expressed in lipidinfiltrated muscle tissues,and the KEGG website predicted that the highly expressed FABP4 might be involved in the regulation of the PPAR γ signaling pathway that closely related to skeletal muscle lipid infiltration.The results of immunohistochemistry（IHC）and q PCR demonstrated that the levels of FABP4,PPAR γ and Interleukin-4（IL-4）in the lipid-infiltrated paravertebral muscle group were evidently higher than those in the normal muscle group（P<0.05）.IL-4 induced elevated lipogenesis in HSMCs.At the same time,the levels of perilipin,adiponectin,FABP4 and PPAR γ proteins increased significantly in the IL-4 treatment group than those in the control group（P<0.05）.Compared with the negative control adenovirus group and the control group,the expression of perilipin,adiponectin,and PPAR γ proteins in the treatment group with the overexpression of FABP4 adenovirus increased evidently,and the lipogenesis was more obvious,the difference was significant（P <0.05）.The addition of FABP4 inhibitor BMS-309403 to HSMCs could reduce the lipogenesis induced by IL-4,and the levels of perilipin,adiponectin,and PPAR γ proteins in the FABP4 inhibitor co-treated with IL-4group were significantly lower than those in the IL-4-treated group（P<0.05）.PPAR γinhibitor GW9662 could also attenuate the lipogenesis of HSMCs.The GW9662 cotreated with IL-4 group significantly reduced lipogenesis and decreased the expression of perilipin and adiponectin than the IL-4-treated group（P<0.05）In addition,when GW9662 was added to the FABP4 adenovirus treatment group,the lipogenesis and the expression of perilipin and adiponectin were significantly decreased than those in the FABP4 adenovirus treatment group（P<0.05）.Conclusion FABP4 promotes lipogenesis in human skeletal muscle cells induced by IL-4 via activating the PPAR γ signaling pathway.Our results provide a clear entry point on the pathogenesis of muscle lipid infiltration and a new target for clinical treatment of muscle lipid infiltration.