PI3K/AKT regulates aggrecan gene expression by modulating Sox9 expression and activity in nucleus pulposus cells of the intervertebral disc

Abstract

The goal of the investigation was to test the hypothesis that the PI3K/AKT signaling pathway regulates the expression of the major extracellular matrix component of the intervertebral disc, aggrecan, in nucleus pulposus cells. Primary rat nucleus pulposus cells were treated with PI3K inhibitor to measure changes in gene and protein expression. In addition, cells were transfected with various luciferase reporter plasmids to investigate mechanisms of regulation of aggrecan gene expression. We found that treatment of nucleus pulposus cells with a PI3K inhibitor, LY294002 resulted in decreased expression of aggrecan and a reduction in deposition of sulfated glycosaminoglycans. Moreover, pharmacological suppression or co-expression of dominant negative (DN)-PI3K or DN-AKT resulted in downregulation of aggrecan promoter activity. Expression of constitutively active (CA)-PI3K significantly induced aggrecan promoter activity. We observed that PI3K maintained Sox9 gene expression and activity: inhibition of PI3K/AKT resulted in decreased Sox9 expression, lowered promoter activity and mediated a reduction in Sox9 transcriptional activity. PI3K effects were independent of phosphorylation status of Cterminus transactivation domain (TAD) of Sox9. Finally, we noted that in nucleus pulposus cells, PI3K signaling controlled transactivation of p300 (p300-TAD activity), an important transcriptional coactivator of Sox9. Results of these studies demonstrate for the first time that PI3K/AKT signaling controls aggrecan gene expression, in part by modulating Sox9 expression and activity in cells of the nucleus pulposus.

Signaling Cascades Governing Cdc42-Mediated Chondrogenic Differentiation and Mensenchymal Condensation

“…However, Ikegami et al (2011) have indicated that Sox9 binds to the promoter and enhances the transcription of PI3Kca (P110a), resulting in an increase of phosphorylated Akt, which promotes chondrocyte survival and hypertrophy. Cheng et al (2009) have demonstrated that PI3K/Akt signaling controls aggrecan gene expression, in part by modulating Sox9 expression and transactivity in nucleus pulposus cells. The discrepancy in our findings could be explained by the different cell types and treatments among these studies.…”

Text-mining network analysis of the response to osmotic stimuli in the intervertebral disc

“…It is an important modulator of extracellular signals, including those elicited by E-cadherin-mediated cell-cell adhesion, which plays an important role in the maintenance of the structural and functional integrity of epithelial tissues (Laprise et al, 2002). In a recent study, Cheng et al (2009) reported that the PI3K/AKT signaling pathway plays an important role in the regulation of aggrecan gene expression in cells of the nucleus pulposus in IVD. Importantly, aggrecan gene expression appears to change in chondrocytes in response to hypo-and hyper-osmotic stimuli (Chen et al, 2002), and IVD cells can secrete a complex extracellular matrix that contains the highly sulfated proteoglycan aggrecan that provides the tissue with its unique osmotic properties (Cheng et al, 2009).…”

“…In a recent study, Cheng et al (2009) reported that the PI3K/AKT signaling pathway plays an important role in the regulation of aggrecan gene expression in cells of the nucleus pulposus in IVD. Importantly, aggrecan gene expression appears to change in chondrocytes in response to hypo-and hyper-osmotic stimuli (Chen et al, 2002), and IVD cells can secrete a complex extracellular matrix that contains the highly sulfated proteoglycan aggrecan that provides the tissue with its unique osmotic properties (Cheng et al, 2009). IL-6 has multiple functions in a wide variety of biological processes, including the immune system, neuronal regulation, hematopoiesis, and inflammation (Gadient and Otten, 1997;Barnes et al, 2011).…”

“…Therefore, IVD cells exposed to physiological mechanical loads experience complex physical stimuli including strain, fluid flow, osmotic and hydrostatic pressure, and compressive, tensile, and shear stresses (Weidenbaum et al, 1992;Urban et al, 1993;Iatridis et al, 1996). IVD cells can secrete a complex extracellular matrix that contains the highly sulfated proteoglycan aggrecan through its interactions with cations and provides the tissue with its unique osmotic properties (Cheng et al, 2009).…”

Lessons from Genomic Profiling in AS

“…Transactivated p300, controlled by phosphoinositide-3 kinase (PI3K)/AKT, is also an important transcriptional co-activator of Sox9, which modulates the expression of the major extracellular matrix component, aggrecan (Cheng et al, 2009). Moreover, there is some evidence supporting a p300 interaction with the Wnt pathway as it is a -catenin transcriptional coactivator.…”