EGF Contributes to Hypertrophy of Human Ligamentum Flavum via the TGF-ß1/Smad3 Signaling Pathway.

Background: The most common spinal disorder in elderly is lumbar spinal canal stenosis (LSCS). Previous studies showed that ligamentum flavum hypertrophy (LFH) with fibrosis as the main pathological change is one of the pathogenic factors leading to LSCS. Epidermal Growth Factor (EGF) is known to have an intimate relationship with fibrosis in various tissues. Nevertheless, currently, there are few studies regarding EGF in LFH. The effect of EGF on the development of LFH is unknown, and the underlying pathomechanism remains unclear. In this study, we investigated the role of EGF in LFH and its potential molecular mechanism. Methods: First, the expression levels of EGF, phosphorylation of EGF receptor (pEGFR), Transforming growth factor-ß1 (TGF-ß1), Phosphorylated Smad3 (pSmad3), collagen I and collagen III were examined via immunohistochemistry and Western blot in LF tissues from patients with LSCS or Non-LSCS. Second, primary LF cells were isolated from adults with normal LF thickness and were cultured with different concentrations of exogenous EGF with or without erlotinib/TGF-ß1-neutralizing antibody. Results: The results showed that EGF, pEGFR, TGF-ß1, pSmad3, collagen I and collagen III protein expression in the LSCS group was significantly higher than that in the Non-LSCS group. Meanwhile, pEGFR, TGF-ß1, pSmad3, collagen I and collagen III protein expression was significantly enhanced in LF cells after exogenous EGF exposure, which can be notably blocked by erlotinib. In addition, pSmad3, collagen I and collagen III protein expression was blocked by TGF-ß1-neutralizing antibody. Conclusions: EGF promotes the synthesis of collagen I and collagen III via the TGF-ß1/Smad3 signaling pathway, which eventually contributes to LFH.

Thrombospondin-1 promotes mechanical stress-mediated ligamentum flavum hypertrophy through the TGFß1/Smad3 signaling pathway.

Lumbar spinal canal stenosis is primarily caused by ligamentum flavum hypertrophy (LFH), which is a significant pathological factor. Nevertheless, the precise molecular basis for the development of LFH remains uncertain. The current investigation observed a notable increase in thrombospondin-1 (THBS1) expression in LFH through proteomics analysis and single-cell RNA-sequencing analysis of clinical ligamentum flavum specimens. In laboratory experiments, it was demonstrated that THBS1 triggered the activation of Smad3 signaling induced by transforming growth factor ß1 (TGFß1), leading to the subsequent enhancement of COL1A2 and α-SMA, which are fibrosis markers. Furthermore, experiments conducted on a bipedal standing mouse model revealed that THBS1 played a crucial role in the development of LFH. Sestrin2 (SESN2) acted as a stress-responsive protein that suppressed the expression of THBS1, thus averting the progression of fibrosis in ligamentum flavum (LF) cells. To summarize, these results indicate that mechanical overloading causes an increase in THBS1 production, which triggers the TGFß1/Smad3 signaling pathway and ultimately results in the development of LFH. Targeting the suppression of THBS1 expression may present a novel approach for the treatment of LFH.

Revealing the novel autophagy-related genes for ligamentum flavum hypertrophy in patients and mice model.

Background: Fibrosis is a core pathological factor of ligamentum flavum hypertrophy (LFH) resulting in degenerative lumbar spinal stenosis. Autophagy plays a vital role in multi-organ fibrosis. However, autophagy has not been reported to be involved in the pathogenesis of LFH. Methods: The LFH microarray data set GSE113212, derived from Gene Expression Omnibus, was analyzed to obtain differentially expressed genes (DEGs). Potential autophagy-related genes (ARGs) were obtained with the human autophagy regulator database. Functional analyses including Gene Ontology (GO), Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment, Gene Set Enrichment Analysis (GSEA), and Gene Set Variation Analysis (GSVA) were conducted to elucidate the underlying biological pathways of autophagy regulating LFH. Protein-protein interaction (PPI) network analyses was used to obtain hub ARGs. Using transmission electron microscopy, quantitative RT-PCR, Western blotting, and immunohistochemistry, we identified six hub ARGs in clinical specimens and bipedal standing (BS) mouse model. Results: A total of 70 potential differentially expressed ARGs were screened, including 50 up-regulated and 20 down-regulated genes. According to GO enrichment and KEGG analyses, differentially expressed ARGs were mainly enriched in autophagy-related enrichment terms and signaling pathways related to autophagy. GSEA and GSVA results revealed the potential mechanisms by demonstrating the signaling pathways and biological processes closely related to LFH. Based on PPI network analysis, 14 hub ARGs were identified. Using transmission electron microscopy, we observed the autophagy process in LF tissues for the first time. Quantitative RT-PCR, Western blotting, and immunohistochemistry results indicated that the mRNA and protein expression levels of FN1, TGFß1, NGF, and HMOX1 significantly higher both in human and mouse with LFH, while the mRNA and protein expression levels of CAT and SIRT1 were significantly decreased. Conclusion: Based on bioinformatics analysis and further experimental validation in clinical specimens and the BS mouse model, six potential ARGs including FN1, TGFß1, NGF, HMOX1, CAT, and SIRT1 were found to participate in the fibrosis process of LFH through autophagy and play an essential role in its molecular mechanism. These potential genes may serve as specific therapeutic molecular targets in the treatment of LFH.