In this study, we investigated the role of heme oxygenase-1 (HO-1) in intervertebral disc degeneration (IDD) by assessing the effects of HO-1 overexpression on IL-1β-induced apoptosis in nucleus pulposus cells (NPCs). Immunohistochemical staining showed HO-1 expression to be lower in NPCs from IDD patients than from patients with lumbar vertebral fractures (LVF). Western blot analysis showed HO-1 and LC3-II/I levels to be lower in NP tissues from IDD patients than from LVF patients, suggesting suppression of autophagy in degenerative intervertebral disc. Consistent with that idea, autophagy was increased in HO-1-overexpressing NPCs while IL-1β-induced apoptosis was reduced. These effects were reversed by treatment with the early autophagy inhibitor 3-methyl adenine, which suggests HO-1-induced autophagy suppresses IL-1β-induced apoptosis in NPCs. HO-1 overexpression promoted autophagy by increasing levels of Beclin-1/PI3KC3 complex. Phospho-P65 levels were lower in HO-1-overexpressing NPCs, suggesting inhibition of NF-κB-mediated apoptosis. Our study thus demonstrates that HO-1 promotes autophagy by enhancing formation of Beclin-1/PI3KC3 complex and suppresses IL-1β-induced apoptosis by inhibiting NF-κB. We suggest that HO-1 is a potential therapeutic target to alleviate IDD.

Our results support the hypothesis that Aβ is involved in the pathogenesis of choroidal neovascularization (CNV) formation by promoting the production of the angiogenic cytokines VEGF, IL-8 and MCP-1 by RPE cells. Mitochondrial ROS was shown to play a role in the regulation of Aβ induced expression of these cytokines.

The intervertebral disc degeneration (IDD) is considered to be an initiator of a series of spinal diseases, among which changes in the nucleus pulposus (NP) are the most significant. NP cells reside in a microenvironment with a lack of blood vessels, hypoxia, and low glucose within the intervertebral disc. Due to the strong activity of HIF-1α, glycolysis is the main pathway for energy metabolism in NP cells. Our previous study found that higher SIRT1 expression is beneficial to delay the degeneration of NP cells. In order to find the downstream genes by which SIRT1 acts on NP cells, we used iTRAQ sequencing to detect the differences between degenerated NP cells overexpressing SIRT1 and a control group (human NP cells were derived from surgery) and found that the expression of LDHA changed in the same direction with SIRT1. This suggests that SIRT1 may delay the degeneration of NP cells by regulating glycolysis. We then used a Seahorse XFe24 analyzer to measure the bioenergetic parameters of NP cells and obtained three findings: (a) glycolysis is the main energy metabolism pathway in NP cells, (b) there is a large difference in ATP production between senescent cells and young cells, and (c) SIRT1 can regulate the production of ATP from glycolysis by regulating LDHA. We also found that SIRT1 in NP cells has a positive regulatory effect on c-Myc which is an upstream gene of LDHA. Through observing IDD-related indicators such as apoptosis, proliferation, senescence, and extracellular matrix, we found that SIRT1 can delay degeneration, and interference with c-Myc and LDHA, respectively, weakens the protective effect of SIRT1. Interfering with LDHA alone can also inhibit glycolysis and accelerate degeneration. Overall, we found that the inhibition of glycolysis in Np cells significantly affects their normal physiological functions and determined that LDHA is a potential therapeutic target for the treatment of IDD.

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