Ectopic expression of Smurf2 and acceleration of age-related intervertebral disc degeneration in a mouse model

Abstract

<jats:sec><jats:title>OBJECTIVE</jats:title><jats:p>Lumbar intervertebral disc degeneration, an age-related process, is a major cause of low-back pain. Although low-back pain is a very common clinical problem in the aging population, no effective treatment is available, largely owing to lack of understanding of the molecular mechanisms underlying disc degeneration. The goal of this study was to characterize how ectopic expression of Smurf2 driven by the collagen Type II alpha 1 (<jats:italic>Col2a1</jats:italic>) promoter alters disc cell phenotype and associated cellular events, matrix synthesis, and gene expression during disc degeneration in mice.</jats:p></jats:sec><jats:sec><jats:title>METHODS</jats:title><jats:p>To characterize how ectopic expression of Smurf2 in <jats:italic>Col2a1</jats:italic>-promoter working cells affects the disc degeneration process, the authors performed histological and immunohistochemical analysis of lumbar spine specimens harvested from wild-type (WT) and <jats:italic>Col2a1-Smurf2</jats:italic> transgenic mice at various ages (n ≥ 6 in each age group). To elucidate the molecular mechanism underlying Smurf2-mediated disc degeneration, the authors isolated cells from WT and <jats:italic>Col2a1-Smurf2</jats:italic> transgenic lumbar intervertebral discs and performed Western blot and real-time RT-PCR (reverse transcription polymerase chain reaction) to examine the protein and mRNA levels of interesting targets.</jats:p></jats:sec><jats:sec><jats:title>RESULTS</jats:title><jats:p>The authors demonstrated that approximately 30% of WT mice at 10–12 months of age had started to show disc degeneration and that the disc degeneration process was accelerated by 3–6 months in <jats:italic>Col2a1-Smurf2</jats:italic> transgenic mice. Chondrocyte-like cell proliferation, maturation, and fibrotic tissue formation in the inner annulus were often accompanied by fibroblast-to-chondrocyte differentiation in the outer annulus in transgenic discs. The chondrocyte-like cells in transgenic discs expressed higher levels of connective tissue growth factor (CTGF) than were expressed in WT counterparts.</jats:p></jats:sec><jats:sec><jats:title>CONCLUSIONS</jats:title><jats:p>The findings that ectopic expression of Smurf2 driven by the <jats:italic>Col2a1</jats:italic> promoter accelerated disc degeneration in <jats:italic>Col2a1-Smurf2</jats:italic> transgenic mice, and that higher levels of CTGF protein and mRNA were present in <jats:italic>Col2a1-Smurf2</jats:italic> transgenic discs, indicate that Smurf2 accelerates disc degeneration via upregulation of CTGF.</jats:p></jats:sec>

LINC00969 promotes the degeneration of intervertebral disk by sponging miR‐335‐3p and regulating NLRP3 inflammasome activation

“…Intervertebral disk degeneration (IDD) is a common spinal disorder characterized by neurological deficits, which is associated with significant morbidity in the elderly population . It is widely accepted that the degeneration and apoptosis of nucleus pulposus cells (NPCs) are the initial factors resulting in IDD .…”

Intervertebral Disc Aging, Degeneration, and Associated Potential Molecular Mechanisms

“…Thus, it is difficult to distinguish the physiologic process of disc aging from that of disc degeneration. In general, when a disc with structural failure is combined with accelerated or advanced signs of aging, it is considered to be a degenerate disc (8,9). Given that the process of disc aging is affected by many risk factors such as genetic inheritance, excessive mechanical loading, obesity, trauma, nutrition, smoking, and inflammation, as well as catabolic cytokines and proteases, disc degeneration occurs in every population worldwide (7).…”

“…However, if the cells were cultured under high glucose, a glucose-mediated oxidative stress was generated and induced senescence (18). Although permeability and metabolite transport decrease in an aging disc due to low water content in the nucleus and fibrotic feature of entire disc, they increase again when the aging disc is herniated or injured due to trauma or repetitive over-loading (19), which presumably leads to an aberrant increase in concentrations of nutrients in the microenvironment adjacent to the structural defects, because cell cloning, senescent cells, and structural defect extension are frequently detected in the areas adjacent to structural defects (20-22; 9). These phenotypic changes imply a correlation between cell proliferation, cell senescence, and matrix breakdown during disc degeneration progression.…”

“…We have recently shown that Col2a1-Smurf2 transgenic mice also exhibit accelerated age-related intervertebral disc degeneration (9). During development of the disc degeneration in these transgenic mice, many phenotypic changes such as fibroblast-to-chondrocyte differentiation, chondrocyte-like cell cloning, migration, and fibrosis, were similar to those occurring in humans and reflected connective tissue growth factor (CTGF) function during wound healing and scleroderma (28).…”

“…During development of the disc degeneration in these transgenic mice, many phenotypic changes such as fibroblast-to-chondrocyte differentiation, chondrocyte-like cell cloning, migration, and fibrosis, were similar to those occurring in humans and reflected connective tissue growth factor (CTGF) function during wound healing and scleroderma (28). Indeed, CTGF expression and secretion is increased in the chondrocyte-like cells that are prone to degenerate in Col2a1-Smurf2 transgenic mouse discs, indicating that Smurf2-mediated disc degeneration is via upregulation of CTGF (9). Because discs possess a limited ability to repair when they are disrupted, tears/clefts in discs are never healed and could cause a persistence of CTGF expression by the cells adjacent to the structural defects due to continuous production and release of TGF-β, an inducer of CTGF expression, by these cells as a cellular response to repetitive excessive deformation of disrupted matrix (29,8,30) (Wu et al, unpublished data).…”