Potential regenerative treatment strategies for intervertebral disc degeneration in dogs

Pain due to spontaneous intervertebral disc (IVD) disease is common in dogs. In chondrodystrophic (CD) dogs, IVD disease typically develops in the cervical or thoracolumbar spine at about 3-7 years of age, whereas in non-chondrodystrophic (NCD) dogs, it usually develops in the caudal cervical or lumbosacral spine at about 6-8 years of age. IVD degeneration is characterized by changes in the biochemical composition and mechanical integrity of the IVD. In the degenerated IVD, the content of glycosaminoglycan (GAG, a proteoglycan side chain) decreases and that of denatured collagen increases. Dehydration leads to tearing of the annulus fibrosus (AF) and/or disc herniation, which is clinically characterized by pain and/or neurological signs. Current treatments (physiotherapy, ant-iinflammatory/ analgesic medication, surgery) for IVD disease may resolve neurological deficits and reduce pain (although in many cases insufficient), but do not lead to repair of the degenerated disc. For this reason, there is interest in new regenerative therapies that can repair the degenerated disc matrix, resulting in restoration of the biomechanical function of the IVD. CD dogs are considered a suitable animal model for human IVD degeneration because of their spontaneous IVD degeneration, and therefore studies investigating cell-, growth factor-, and/or gene therapy-based regenerative therapies with this model provide information relevant to both human and canine patients. The aim of this article is to review potential regenerative treatment strategies for canine IVD degeneration, with specific emphasis on cell-based strategies.