Short Link N Stimulates Intervertebral Disc Repair in a Novel Long-Term Organ Culture Model that Includes the Bony Vertebrae.

Link N (DHLSDNYTLDHDRAIH) is a peptide that occurs naturally in the intervertebral discs (IVDs) and cartilage as a result of proteolytic cleavage of Link protein. Several studies have identified Link N as a growth factor capable of stimulating matrix synthesis in these tissues. We have recently discovered that annulus fibrosus cells can release an enzyme (possibly cathepsin K) that can further cleave Link N resulting in an eight amino acid peptide, we called short Link N (sLink N). Separately, we recently developed and validated an organ culture model that has the vertebrae attached (vIVDs; IVD with intact vertebrae). The aims of this study were (i) to examine if sLink N has the potential to repair early degenerate discs and (ii) to determine if this new model can be used to test potential drugs for disc repair. To determine if sLink N was able to stimulate repair of the degenerate disc, vIVDs with trypsin-induced degeneration (DG) were used. After 4 weeks of culture, the proteoglycan content measured as glycosaminoglycans was stimulated by sLink N in the degenerated discs, and the staining of proteoglycan was observed throughout the tissue irrespective of its proximity to the cells. The quantity of extractable type II collagen and aggrecan was also increased when the degenerate discs were treated with sLink N. Taken together, the results suggest that sLink N can increase key disc matrix molecules, namely type II collagen and aggrecan. Thus sLink N is an attractive peptide for tissue engineering and regeneration of the disc due to its anabolic effects. Finally, we show the feasibility of using the long-term whole organ culture system with adjacent intact vertebrae for studying the DG and regeneration of the IVD.