CCN2/CTGF is required for matrix organization and to protect growth plate chondrocytes from cellular stress

Abstract

CCN2 (connective tissue growth factor (CTGF/CCN2)) is a matricellular protein that utilizes integrins to regulate cell proliferation, migration and survival. The loss of CCN2 leads to perinatal lethality resulting from a severe chondrodysplasia. Upon closer inspection of Ccn2 mutant mice, we observed defects in extracellular matrix (ECM) organization and hypothesized that the severe chondrodysplasia caused by loss of CCN2 might be associated with defective chondrocyte survival. Ccn2 mutant growth plate chondrocytes exhibited enlarged endoplasmic reticula (ER), suggesting cellular stress. Immunofluorescence analysis confirmed elevated stress in Ccn2 mutants, with reduced stress observed in Ccn2 overexpressing transgenic mice. In vitro studies revealed that Ccn2 is a stress responsive gene in chondrocytes. The elevated stress observed in Ccn2−/− chondrocytes is direct and mediated in part through integrin α5. The expression of the survival marker NFκB and components of the autophagy pathway were decreased in Ccn2 mutant growth plates, suggesting that CCN2 may be involved in mediating chondrocyte survival. These data demonstrate that absence of a matricellular protein can result in increased cellular stress and highlight a novel protective role for CCN2 in chondrocyte survival. The severe chondrodysplasia caused by the loss of CCN2 may be due to increased chondrocyte stress and defective activation of autophagy pathways, leading to decreased cellular survival. These effects may be mediated through nuclear factor κB (NFκB) as part of a CCN2/integrin/NFκB signaling cascade.Electronic supplementary materialThe online version of this article (doi:10.1007/s12079-013-0201-y) contains supplementary material, which is available to authorized users.

FGFR3/fibroblast growth factor receptor 3 inhibits autophagy through decreasing the ATG12–ATG5 conjugate, leading to the delay of cartilage development in achondroplasia

“…Further, we examined the expression of ATG5 and FGFR3 in the tibia growth plate from postnatal d 5 WT mice. Consistent with the expression pattern of ATG12 reported in a previous study, 29 we found that immunoreactive ATG5 particles were observed mainly in cells in the proliferative, prehypertrophic and hypertrophic zones, which were overlapped with the expression of FGFR3 (Fig. 6E).…”

“…20,59 Impaired autophagy is involved in the pathogenesis of chondrodysplasia resulting from the loss of Sumf1 or Ctgf/Ccn2, in which, chondrocyte viability is profoundly reduced because of the lack of protection from autophagy. 28,29 As the most common genetic form of dwarfism in humans, achondroplasia is characterized by the retarded bone growth with strongly impaired cell viability, including inhibited proliferation, delayed differentiation and increased apoptosis. 12,60,61 The phenotype similarity between mice with ACH and loss of Sumf1 or Ctgf/Ccn2 suggests that impaired autophagy may play a role in the pathogenesis of achondroplasia as well.…”

“…28 Inactivation of CTGF/ CCN2 (connective tissue growth factor) in mice leads to severe chondrodysplasia resulting from increased stress-induced death and decreased autophagy. 29 All these findings suggest that impaired autophagy will result in abnormal cartilage development. However, the role of autophagy in achondroplasia is not well understood.…”

Cellular and molecular actions of CCN2/CTGF and its role under physiological and pathological conditions

“…CCN2 is principally produced by chondrocytes immediately before their hypertrophic differentiation, is transported from the chondrocytes to target cells and indeed promotes all of the processes that operate for endochondral ossification [1,49,50], which is typically represented by the phenotype observed in Ccn2null mice with remarkable skeletal defects [1,49,51]. Two other recent reports indicate such a role of CCN2 in intervertebral disc development and palatogenesis as well [52,53].…”

New functional aspects of CCN2 revealed by trans-omic approaches

“…This particular CCN family member plays significant roles in physiological development [7][8][9][10][11][12][13][14][15], wound healing [16], and in the pathological fibrotic remodeling of multiple tissues, organs [17][18][19][20][21][22][23][24][25][26][27][28], and malignancies throughout the body [3,5]. CCN2 is required for the proper development of the olfactory central nervous system [29], pancreas [30], hair follicles [31], and skeletal system [11]; hence, Ccn2-null mice die upon delivery [32,33]. CCN2 is also known to be involved in multiple steps of orofacial development [34,35].…”