Integrin-mediated interactions with a laminin-presenting substrate modulate biosynthesis and phenotypic expression for cells of the human nucleus pulposus

Abstract

With aging and pathology, cells of the nucleus pulposus (NP) de-differentiate towards a fibroblast-like phenotype, a change that contributes to degeneration of the intervertebral disc (IVD). Laminin isoforms are a component of the NP extracellular matrix during development but largely disappear in the adult NP tissue. Exposing human adult NP cells to hydrogels made from PEGylated-laminin-111 (PEGLM) has been shown to regulate NP cell behaviors and promote cells to assume a biosynthetically active state with gene/protein expression and morphology consistent with those observed in juvenile NP cells. However, the mechanism regulating this effect has remained unknown. In the present study, the integrin subunits that promote adult degenerative NP cell interactions with laminin-111 are identified by performing integrin blocking studies along with assays of intracellular signaling and cell phenotype. The findings indicate that integrin α3 is a primary regulator of cell attachment to laminin and is associated with phosphorylation of signaling molecules downstream of integrin engagement (ERK 1/2 and GSK3β). Sustained effects of blocking integrin α3 were also demonstrated including decreased expression of phenotypic markers, reduced biosynthesis, and altered cytoskeletal organization. Furthermore, blocking both integrin α3 and additional integrin subunits elicited changes in cell clustering, but did not alter the phenotype of single cells. These findings reveal that integrin- mediated interactions through integrin α3 are critical in the process by which NP cells sense and alter phenotype in response to culture upon laminin and further suggest that targeting integrin α3 has potential for reversing or slowing degenerative changes to the NP cell.

The Proteolysis of ECM in Intervertebral Disc Degeneration

“…At least 15 Laminin isoforms are formed by the combination of three different peptide chains, and multiple Laminin isoforms and their receptors are expressed in IVD tissues [38]. In addition, integrin-mediated interaction with Laminin regulates the phenotype of NP cells [39].…”

“…Available evidence suggests that the response of nucleus pulposus cells to sustained mechanical stimuli is closely related to disc degeneration [16,56]. Furthermore, alterations in ECM composition modulate NP cell behavior by directly affecting cell-ECM interactions without altering the mechanical environment [39,57]. Dysregulation of ECM homeostasis is closely related to the process of disc degeneration, and proteolysis of the ECM occurs at the beginning of this process.…”

Roles of focal adhesion proteins in skeleton and diseases

“…According to their expression levels, integrins expressed in human IVDs can be divided into five groups ( Fig. 4 ): high expression group ( α 1, α 5, α v, β 1, β 3, β 5), low expression group ( β 2, β 4, β 6), controversial expression group ( α 2, α 3, α 6), no expression group ( α 4, α IIb) and expression unexplored group ( α 7, α 8, α 9, α 10, α 11, α D, α E, α L, α M, α X, β 7, β 8) 116 , 117 , 118 , 119 , 120 , 121 , 122 . In the controversial expression group, previous study showed that integrins α 2, α 3, α 6 were not expressed in human IVD tissues 116 , but some studies demonstrated that they could be detected in human NP tissues and cells 120 , 121 , 122 .…”

Intervertebral Disc Degeneration: Biomaterials and Tissue Engineering Strategies toward Precision Medicine

“…A study reported that a series of laminin‐mimetic peptide poly(ethylene) glycol (PEG) hydrogels modulated integrin and syndecan binding in NP cells, thus promoting ECM biosynthesis [ 76 ] primarily through integrin α 3 mediated interaction with laminin, which also associated with phosphorylation of signaling molecules of extracellular‐signal‐regulated kinase (ERK1/2) and glycogen synthase kinase (GSK3 β ). [ 77 ]…”