Ablation of VEGFA following a lumbar intervertebral disc injury attenuates intradiscal neurovascular features and prevents chronic low back pain symptoms
There are currently no therapies for the staggering disability and public health costs of chronic low back pain (LBP). Innervation of the degenerating intervertebral disc (IVD) is suspected to cause discogenic LBP, but the mechanisms that orchestrate the IVD's neo-innervation and subsequent symptoms of LBP remain unknown. We hypothesize that Vascular Growth Endothelial Factor-A (VEGFA) critically mediates the neurite invasion in the IVD and contributes to prolonged LBP.  Initiating IVD degeneration through a mechanical injury, we evaluated the progression of neurovascular features into the IVD, as well as resultant LBP symptoms and locomotive performance at acute (3-weeks) and prolonged (12-weeks) time points following IVD injury. To determine the role of VEGFA, we used a mouse model with ubiquitous inducible recombination of the floxed VEGFA allele (UBC-CreERT2; VEGFAfl/fl).  The ablation of VEGFA attenuated the neurite and vessel infiltration into the degenerating IVD, and the VEGFA-null animals exhibited alleviated mechanical allodynia and improved locomotive performance. To determine the effects of IVD-derived VEGFA on endothelial cells and neurons, we cultured HMEC-1 endothelial cells and SH-SY5Y neurons using conditioned media from VEGFA-silenced (siRNA) human primary IVD cells stimulated by IL1b.  The endothelial cells and neurons exposed to the secretome of the VEGFA-silenced IVD cells exhibited reduced growth, suggesting that the inhibition of IVD-derived VEGFA may be sufficient to attenuate intradiscal neurovascular features. Together, we show that VEGFA orchestrates the growth of intradiscal vessels and neurites that cause low back pain and impaired function, and the inhibition of VEGFA can prevent prolonged low back pain. Overall design: Human intervertebral disc (IVD) cells were isolated from the IVD tissue of eight patients removed during elective discectomy surgeries. IVD cells were plated and 1 ng/mL of IL-1ß was added to the stimulate the cells for 24 hours. IL-1ß was removed and cells were then transfected with Control, Scrambled siRNA (Scram) or VEGF siRNA (Vegfa)for 24 hours. Next, the IL-1ß stimulated and siRNA transfected IVD cells were co-cultured with either SH-SY5Y neuronal cells (Nerves) for 48 hours or HMEC-1 endothelial cells (Endo) for 24 hours. The co-cultured nerve and endothelial csells were submitted for RNA sequencing.