Revealing the Dynamic Association Between Lymphatic Endothelial Cell Markers and Intervertebral Disk Degeneration

Objective: This study aims to analyze the dynamic changes in lymphatic endothelial cell (LEC) markers during the progression of intervertebral disk degeneration (IDD) and to investigate their association with the progression of IDD. Method: In this study, intervertebral disk (IVD) specimens were first collected from patients who underwent open lumbar fusion surgery for spinal fractures (control group, n = 10) and lumbar disk herniation (IDD group, n = 10). Concurrently, a mouse IDD model was established, and IVD specimens were collected from mouse in the Sham group and the IDD group 1, 3, and 6 weeks after modeling (n = 5 per group at each time point). Pathological morphological changes in human and mouse IVD specimens were observed using Hematoxylin and Eosin (H&E) and Masson's Trichrome staining. The degree of degeneration in the mouse IVD specimens was quantified using a histopathological scoring system. Subsequently, real-time quantitative polymerase chain reaction (RT-qPCR), immunohistochemistry (IHC), and immunofluorescence (IF) staining were employed to examine LEC markers in IVD tissue, including lymphatic vessel endothelial hyaluronan receptor 1 (LYVE-1), podoplanin (PDPN), prospero homeobox protein 1 (PROX-1), and vascular endothelial growth factor receptor 3 (VEGFR-3), as well as matrix metabolism-related markers such as matrix metalloproteinase 13 (MMP-13) and collagen II (Col II). Finally, we performed Spearman's rank correlation analysis between the histopathological scores of all mouse IVD specimens and the corresponding expression levels of LEC markers. Results: In human IVD tissue, expression levels of LYVE-1, PDPN, PROX-1, and VEGFR-3 were extremely low in the normal group. In contrast, expression of these markers was significantly upregulated in the IDD group. In the mouse IDD model, compared with the Sham group at the same time point, the IDD group exhibited higher histopathological scores in IVD tissue, accompanied by upregulation of LYVE-1, PDPN, PROX-1, and MMP-13, as well as downregulation of Col II. In-depth analysis revealed that these differences between the Sham and IDD groups were not static but exhibited a dynamic pattern of increasing magnitude over time. Concurrently, as the modeling period progressed, the histopathological scores of mouse IVD in the IDD group, as well as the expression levels of LYVE-1, PDPN, PROX-1, and MMP-13, showed a progressive upward trend, while Col II expression progressively decreased. In addition, Spearman's rank correlation analysis revealed that the expression levels of LYVE-1, PDPN, and PROX-1 in mouse IVD tissue were all significantly positively correlated with histopathological scores. Conclusions: In the process of IDD, the dynamic upregulation of LEC markers is highly consistent with its severity in the time dimension. At the same time, there was also a significant positive correlation between the expression level of LEC markers and the severity of IDD. Taken together, these findings suggest that the dynamic upregulation of LEC markers may be potentially associated with the pathological progression of IDD.