N-cadherin is Key to Expression of the Nucleus Pulposus Cell Phenotype under Selective Substrate Culture Conditions

Abstract

Nucleus pulposus (NP) cells of the intervertebral disc are essential for synthesizing extracellular matrix that contributes to disc health and mechanical function. NP cells have a unique morphology and molecular expression pattern derived from their notochordal origin, and reside in N-cadherin (CDH2) positive cell clusters in vivo. With disc degeneration, NP cells undergo morphologic and phenotypic changes including loss of CDH2 expression and ability to form cell clusters. Here, we investigate the role of CDH2 positive cell clusters in preserving healthy, biosynthetically active NP cells. Using a laminin-functionalized hydrogel system designed to mimic features of the native NP microenvironment, we demonstrate NP cell phenotype and morphology is preserved only when NP cells form CDH2 positive cell clusters. Knockdown (CRISPRi) or blocking CDH2 expression in vitro and in vivo results in loss of a healthy NP cell. Findings also reveal that degenerate human NP cells that are CDH2 negative can be promoted to re-express CDH2 and healthy, juvenile NP matrix synthesis patterns by promoting cell clustering for controlled microenvironment conditions. This work also identifies CDH2 interactions with β-catenin-regulated signaling as one mechanism by which CDH2-mediated cell interactions can control NP cell phenotype and biosynthesis towards maintenance of healthy intervertebral disc tissues.

Dynamic Compression Promotes the Matrix Synthesis of Nucleus Pulposus Cells Through Up-Regulating N-CDH Expression in a Perfusion Bioreactor Culture

“…N-CDH-mediated signaling is helpful to maintain a normal NP cell phenotype and NP matrix synthesis in vitro [29, 30]. In this study, N-CDH up-regulation coincided with better maintenance of the NP cell phenotype and NP matrix synthesis in the dynamic compression group.…”

“…As an important molecule that is helpful to maintain a normal NP cell phenotype and NP matrix synthesis in vitro [29], results showed that N-CDH expression in the dynamic compression group was increased both at gene and protein levels compared with those in the static compression group and the control group (Fig. 4A).…”

“…Furthermore, N-CDH is highly expressed in normal disc NP cells compared with the expression in degenerative NP cells, adjacent disc AF cells and CEP cells [27, 28]. In addition, N-CDH-mediated signaling is helpful to maintain the normal NP cell phenotype and NP matrix synthesis in vitro [29-32]. However, whether N-CDH-mediated signaling is responsible for the positive effects of dynamic compression on NP cell biology remains unknown.…”

N-Cadherin Maintains the Healthy Biology of Nucleus Pulposus Cells under High-Magnitude Compression

“…It is also worth mentioning that N-CDH expression decreases with disc aging and disc degeneration and that the decrease in N-CDH expression coincides with those degenerative disc changes [15, 16]. Hence, several research teams have proposed and verified that N-CDH-mediated signaling is necessary for maintaining normal NP biology [17, 18]. In this study, high-magnitude (20% deformation) compression significantly down-regulated N-CDH expression compared with low-magnitude (2% deformation) compression.…”

“…Recently, several studies have demonstrated that N-CDH is a specific molecule that is highly expressed in normal disc NP cells compared with degenerative NP cells, adjacent disc annulus fibrosus cells and cartilage endplate cells [15, 16]. In addition, N-CDH-mediated signaling helps to maintain the normal juvenile NP phenotype and NP matrix synthesis in vitro [17, 18]. Finally, N-CDH can regulate cell behaviors, cell phenotypes and other pathological phenomena in other tissues [13, 14].…”