I find myself wondering whether a useful testing step between mice and people might be the community of small dogs with IVDD. French bulldogs, dachshunds, and corgis seem particularly susceptible and many of them wind up with rear paralysis. https://www.thedogsdown.com/how-can-ivdd-cause-paralysis/
My wife works on regenerative medicine for spine and they use dogs (and horses) a lot. Cells are similar and they suffer from the same problems. It's mostly dogs who die of natural causes though as dogs are too cute to experiment on...
You’d like to think that, but we’ve had multiple beagle rescues who would disagree. And they were the control population because the actual test subjects get killed.