Functional impact of integrin α5β1 on the homeostasis of intervertebral discs: a study of mechanotransduction pathways using a novel dynamic loading organ culture system

Abstract

BACKGROUND CONTEXT Intervertebral disc (IVD) degeneration, a major cause of low back pain, is considered to be induced by daily mechanical loading. Mechanical stress is widely known to affect cell survival and extracellular matrix metabolism in many cell types. Although the involvement of integrin α5β1 transmembrane mechanoreceptor in IVD degeneration has been reported, the precise function of integrin α5β1 remains obscure. PURPOSE To reflect IVD tissue response to mechanical stress using a dynamic loading organ culture system and elucidate the functional impact of integrin α5β1 on the pathomechanism of IVD degeneration. STUDY DESIGN An ex vivo study using a dynamic loading organ culture system. METHODS Ninety-six rat IVD explants were examined. Intervertebral discs were subjected to 1.3 MPa, 1.0 Hz dynamic compressive load in the presence or absence of an Arg-Gly-Asp (RGD) peptide with affinity to the fibronectin binding-site of integrin α5β1. Cell viability and histomorphology were assessed. The localization of integrin α5β1 in the IVD was assessed by immunohistochemistry. Gene expression levels of IVD cells were evaluated using real-time reverse transcription-polymerase chain reaction. RESULTS In the nucleus pulposus (NP), cell density and viability were reduced by dynamic compressive load. Histologic degenerative alterations, mainly seen in the NP, were the morphologic changes of NP cells. In both NP and annulus fibrosus (AF), immunohistochemistry revealed localization of integrin α5β1 and that the messenger-RNA expression of integrin α5β1 was increased by dynamic load. Dynamic load induced a catabolic effect, the stimulation of matrix metalloproteinase-3 and -13 gene expressions by NP and AF cells. The RGD peptide partially blocked the histologic alterations and the catabolic effect. CONCLUSIONS The dynamic loading organ culture system simulated cellular responses to mechanical loading of the IVD. Our results suggest that IVD cells recognize the mechanical stress through RGD integrins, particularly the α5β1 subtype that is highly expressed in NP and AF cells. Further experiments using this system will provide information about pathomechanisms of IVD degeneration through the mechanotransduction pathways.

The role of angiopoietin-2 in nucleus pulposus cells during human intervertebral disc degeneration

“…Integrins participate in mechanotransduction in human NP cells by acting as mechanoreceptors that detect mechanical stimulation by dynamic loading. 33 Although Tie2 is a Ang-2 receptor, it is capable of forming a complex with integrins. Numerous studies have suggested that Ang-2 exhibits context-dependent functions, eg, It acts as a vessel-destabilizing molecule in Tie2expressing ECs and as a directly pro-angiogenic molecule in Tie2-negative angiogenic ECs via integrin signaling.…”

Matrisome Profiling During Intervertebral Disc Development And Ageing

“…With respect to pathway term enrichment, ECM-receptor interaction, focal adhesion, integrin and TGF- β signalling, were expected, given that most of these pathways are connected. In most of the tissues, integrin cell surface receptors mediate cell-matrix interactions, which are key to control adhesion, survival and differentiation, among others, in response to environmental cues, like mechanical stimuli 45 , 46 . Moreover, focal adhesion kinase (FAK) has been shown to be activated in response to strain in non-degenerate disc cells, in an integrin dependent manner 47 .…”

“…Fibronectin (FN) mediates a wide variety of cellular interactions with the matrix and plays important roles in cell adhesion, migration, growth, differentiation and survival, particularly through integrin interactions 4 , 46 . It interacts with a broad range of collagens (type I, II, III, IV, V and X) 49 and, in line with our results, FN has been shown to be upregulated in numerous models of disc ageing and degeneration 35 , 39 , 50 .…”

Mechanotransduction and cell biomechanics of the intervertebral disc

“…Although one study found that physiological level of dynamic compression induced integrin α5β1 expression in rat disc explants 187 , other studies find that degenerative static compressive loading in vivo upregulate β1 expression in NP cells, and activates downstream signaling 188 .…”

“…Although one study found that physiological level of dynamic compression induced integrin α5β1 expression in rat disc explants, other studies find that degenerative static compressive loading in vivo upregulate β1 expression in NP cells, and activates downstream signaling. Moreover, disruption of β1 integrin signaling may underlie disc cell apoptosis induced by mechanical stress in disc degeneration models.…”