Activation of JNK/p38 MAPK Signaling Pathway by lncRNA DGCR5 Promotes Nucleus Pulposus Cell Degeneration and Pyroptosis in Intervertebral Disk Degeneration.

Objective: Currently, the role of long noncoding RNA (lncRNA) DiGeorge syndrome critical region gene 5 (DGCR5) in intervertebral disk degeneration (IDD) remains unclear. This study explored the molecular mechanisms of how lncRNA DGCR5 promoted human nucleus pulposus cells (NPCs) degeneration and pyroptosis during IDD.

Methods: NPCs were identified by microscopic observation, flow cytometry, and immunofluorescence. An in vitro NPC degeneration model was induced using lipopolysaccharides treatment. SP600125 and SB203580 were used to inhibit the c-Jun N-terminal kinase (JNK) and p38 MAPK signaling, respectively. Quantitative real-time polymerase chain reaction or Western blot was performed to detect lncRNA DGCR5, JNK, phospho-JNK, p38 MAPK, and phospho-p38 MAPK expressions in nucleus pulposus tissues and NPCs. Cell Counting Kit-8 assay was conducted to detect NPC activity. Western blot was performed to detect the expression levels of extracellular matrix-associated proteins (including collagen II, aggrecan, and matrix metalloproteinase 3 [MMP3]) and pyroptosis-associated proteins (including nucleotide oligomerization domain-like receptors family pyrin domain containing 3), cleaved caspase-1, lactate dehydrogenase, and N-terminal fragment of Gasdermin D (GSDMD) in NPCs. Enzyme-linked immunosorbent assay was conducted to detect the expressions of interleukin (IL)-1beta (IL-1β) and IL-18 in NPC supernatants.

Results: DGCR5 was upregulated, and the JNK/p38 MAPK signaling was activated both in nucleus pulposus tissues of IDD patients and lipopolysaccharides-induced NPCs. Inhibition of the JNK/p38 MAPK signaling enhanced NPC proliferation, promoted collagen II and aggrecan expression, while inhibited MMP 3 expression. Silencing of DGCR5 suppressed JNK/p38 MAPK signaling activity, inhibited NPC proliferation, and reduced collagen II and aggrecan expression but promoted MMP 3 expression. Similar findings were also observed for the expressions of nucleotide oligomerization domain-like receptors family pyrin domain containing 3, cleaved caspase-1, N-terminal fragment of GSDMD, IL-1β, and IL-18 as well as the released lactate dehydrogenase level. However, overexpression of DGCR5 yielded opposite results.

Conclusions: These data suggest that lncRNA DGCR5 regulates NPC degeneration and pyroptosis to promote IDD through the JNK/p38 MAPK signaling pathway.