TGFβ regulates Galectin-3 expression through canonical Smad3 signaling pathway in nucleus pulposus cells: implications in intervertebral disc degeneration

Galectin-3 is highly expressed in notochordal nucleus pulposus (NP) and thought to play important physiological roles; however, regulation of its expression remains largely unexplored. The aim of the study was to investigate if TGF beta regulates Galectin-3 expression in NP cells. TGF beta treatment resulted in decreased Galectin-3 expression. Bioinformatic analysis using JASPAR and Matinspector databases cross-referenced with published ChIP-Seq data showed nine locations of highly probable Smad3 binding in the LGALS3 proximal promoter. In NP cells, TGF beta treatment resulted in decreased activity of reporters harboring several 5' deletions of the proximal Galectin-3 promoter. While transfection of NP cells with constitutively active (CA)-ALK5 resulted in decreased promoter activity, DN-ALK5 blocked the suppressive effect of TGF beta on the promoter. The suppressive effect of Smad3 on the Galectin-3 promoter was confirmed using gain- and loss-of-function studies. Transfection with DN-Smad3 or Smad7 blocked TGF beta mediated suppression of promoter activity. We also measured Galectin-3 promoter activity in Smad3 null and wild type cells. Noteworthy, promoter activity was suppressed by TGF beta only in wild type cells. Likewise, stable silencing of Smad3 in NP cells using sh-Smad3 significantly blocked TGF beta-dependent decrease in Galectin-3 expression. Treatment of human NP cells isolated from tissues with different grades of degeneration showed that Galectin-3 expression was responsive to TGF-beta-mediated suppression. Importantly, Galectin-3 synergized effects of TNF-alpha on inflammatory gene expression by NP cells. Together these studies suggest that TGF beta, through Smad3 controls Galectin-3 expression in NP cells and may have implications in the intervertebral disc degeneration. (C) 2015 Elsevier B.V. All rights reserved.