Development of an in vivo mouse model of discogenic low back pain

Abstract

Discogenic low back pain (DLBP) is extremely common and costly. Effective treatments are lacking due to DLBP's unknown pathogenesis. Currently, there are no in vivo mouse models of DLBP, which restricts research in this field. The aim of this study was to establish a reliable DLBP model in mouse that captures the pathological changes in the disc and allows longitudinal pain testing. The model was generated by puncturing the mouse lumbar discs (L4/5, L5/6, and L6/S1) and removing the nucleus pulposus using a microscalpel under the microscope. Histology, molecular pathways, and pain-related behaviors were examined. Over 12 weeks post-surgery, animals displayed the mechanical, heat, and cold hyperalgesia along with decreased burrowing and rearing. Histology showed progressive disc degeneration with loss of disc height, nucleus pulposus reduction, proteoglycan depletion, and annular fibrotic disorganization. Immunohistochemistry revealed a substantial increase in inflammatory mediators at 2 and 4 weeks. Nerve growth factor was upregulated from 2 weeks to the end of the experiment. Nerve fiber ingrowth was induced in the injured discs after 4 weeks. Disc-puncture also produced an upregulation of neuropeptides in dorsal root ganglia neurons and an activation of glial cells in the spinal cord dorsal horn. These findings indicate that the cellular and structural changes in discs, as well as peripheral and central nervous system plasticity, paralleled persistent, and robust behavioral pain responses. Therefore, this mouse DLBP model could be used to investigate mechanisms underlying discogenic pain, thereby facilitating effective drug screening and development of treatments for DLBP.

Link N as a therapeutic agent for discogenic pain

“…Recently, we modeled discogenic pain in a slowly progressive surgical mouse model of discogenic low back pain, induced by stabbing the lumbar discs (L4/5, L5/6, and L6/S1) and removing a part of the NP and monitor pain‐related behaviors longitudinally over 12 weeks. Future studies will determine the effect of Link N on pain in this mouse model by either administering Link N prophylactically starting at time of surgery for 8 weeks or whether the disease can be modulated when targeted therapeutically.…”

Absence of VEGFR‐1/Flt‐1 signaling pathway in mice results in insensitivity to discogenic low back pain in an established disc injury mouse model

“…vegfr‐1 TK − / − mice ( n = 20) and wild‐type mice ( n = 20) aged 4 months were used in the experiment according to a protocol. Disc degeneration was surgically induced using an anterior extraperitoneal approach as described previously (Shi & Das et al, ). Briefly, mice were positioned in the supine position under inhalation anesthesia.…”

“…Postsurgery pain was also assessed at different time points until the designated sacrifice time. The methods applied for testing included von Frey filament testing for mechanical allodynia, hot plate testing for thermal hyperalgesia, and burrowing testing for spontaneous behavioral changes, as described previously (Shi & Das et al, ; Shi & Qiu et al, ). At the designated time after finishing all the pain behavioral tests, the mice were killed under anesthesia with intraperitoneal injection of ketamine and xylazine.…”

“…Safranin O/Fast green (SO/FG) staining was done following the protocol to assess histological changes in IVDs. Two blinded investigators analyzed the results using a modified Masuda scale (Masuda et al, ; Shi & Das et al, ).…”

“…Detailed immunofluorescence staining was described in a previous report (Shi & Das et al, ). Briefly, after deparaffinization and rehydration in downgraded ethanol, the samples were incubated for 30 min (37℃) for antigen retrieval and then blocked for 30 min (room temperature).…”