Beta-defensin 1 knockdown ameliorates the characteristics of intervertebral disc degeneration in a rat model by altering nucleus pulposus and annulus fibrosus cell phenotypes via suppression of the extracellular signal-regulated kinase signaling pathway.

Abstract

Objective: Beta-defensin 1 (DEFB1), is a member of the defensin family involved in inflammation, cell apoptosis and senescence. We hypothesized that DEFB1 is essential for intervertebral disc (IVD) homeostasis. Our objective was to elucidate the roles of DEFB1 in IVD degeneration (IDD).

Design: DEFB1 expression in human degenerated and non-degenerated IVD tissues was measured. In the rat coccygeal IDD model, morphological changes and extracellular signal-regulated kinase 1/2 (ERK1/2) expression were assessed following DEFB1 knockdown lentivirus injection into rat tail discs. In vitro, DEFB1 knockdown or DEFB1-overexpressing plasmid was transfected into NP and AF cells. Under interleukin (IL)-1β stimulation, protein expression, cytokine levels, cell viability, cell senescence, cell apoptosis and cell cycle were evaluated.

Results: IDD tissue from human and rat models exhibited higher DEFB1 levels compared to non-degenerated IVD samples. DEFB1 knockdown ameliorated histopathological changes and reduced inflammation in rat IVD tissues. Under IL-1β stimulation, DEFB1 knockdown increased cell viability (NP cells mean difference 0.28 [95% confidence interval: 0.21, 0.35], AF cells 0.24 [0.20, 0.29]), and decreased cell senescence (-11.78 [-13.73, -9.83], -11.88 [-13.89, -9.87]), cell apoptosis (-9.15 [-11.20, -7.11], -7.40 [-9.36, -5.44]), and G1-phase arrest (-16.74 [-19.87, -13.61], -18.70 [-22.13, -15. 27]) in NP and AF cells. Conversely, DEFB1 overexpression had the opposite effects. DEFB1 knockdown reduced ERK1/2 phosphorylation in vivo and in vitro. The ERK antagonist ameliorated DEFB1 overexpression-induced changes in cellular phenotype.

Conclusions: DEFB1 knockdown ameliorated IDD features, potentially by regulating ERK signaling in NP and AF cells. Targeting DEFB1 could be a promising therapeutic strategy for IDD.