An Analysis of the Early Events When Oligodendrocyte Precursor Cells Are Triggered to Differentiate by Thyroid Hormone, Retinoic Acid, or PDGF Withdrawal

Abstract

Oligodendrocyte precursor cells withdraw from the cell cycle and terminally differentiate after a limited number of cell divisions. The timing of cell-cycle withdrawal and differentiation is controlled by an intrinsic timer, which consists of a timing component that measures elapsed time and an effector component that arrests the cell cycle and initiates differentiation. The effector component can be triggered by either thyroid hormone (TH) or retinoic acid (RA). In this study we investigate how TH and RA act to trigger differentiation. We show the following: (1) Synthetic retinoids that can inhibit AP-1 transcription factors but do not activate gene transcription cannot trigger the effector mechanism, suggesting that TH and RA do not act only by inhibiting AP-1 activity as previously suggested. (2) Both TH and RA induce a transcriptionally dependent antigenic change in purified precursor cells within 2-4 h. (3) Unexpectedly, even before they differentiate, the precursor cells express ceramide galactosyltransferase (CGT), the enzyme that catalyzes the final step in the synthesis of galactocerebroside, an early marker of oligodendrocyte differentiation. (4) Neither TH nor RA directly activates the transcription of the CGT gene, a number of immediate early genes, or the genes that encode any of the known cyclin-dependent kinase inhibitors. (5) The withdrawal of the mitogen platelet-derived growth factor (PDGF), but not TH or RA treatment, causes a rapid decrease in c-fos, NGFI-A/Krox-24, and cyclin D2 mRNA, even though all three treatments trigger cell-cycle arrest and differentiation. (6) PDGF withdrawal and TH treatment, but not RA treatment, induce an increase in cyclin D3 mRNA within 4 h. Thus, we have not found any early changes in gene expression that occur with all three treatments that trigger oligodendrocyte differentiation.

Initiation of Oligodendrocyte Progenitor Cell Migration by a PDGF-A Activated Extracellular Regulated Kinase (ERK) Signaling Pathway

“…We show no increase in the activation of caspase-3 in OP cells up to 72 h after withdrawal of the PDGF-A. Previously published studies have shown that PDGF-A is required for cell survival [7,9,12] and is essential to inhibit both OP differentiation and cell death [23]. Our findings differ from these previous studies in two distinct ways, (1) after 30 min exposure to PDGF-A, OP cells do not die when PDGF-A is withdrawn.…”

“…Previous studies have indicated that PDGF withdrawal causes increased OP death [23]. We assessed the extent of cell death 72 h after 30 min exposure to PDGF, using caspase-3 activation and propidium iodide.…”

3,3′,5-Triiodo-l-thyronine inhibits ductal pancreatic adenocarcinoma proliferation improving the cytotoxic effect of chemotherapy

“…The hPANC-1 and Capan1 cells were responsive to T 3 treatment, HPAC cells were, instead, not influenced by the hormone treatment. The T 3 -dependent cell growth inhibition was also confirmed by FACS analysis indicating a substantial reduction of cell population entering in S phase and evidencing an increase in the percentage of resting cells in G 0 /G 1 phase of the cell cycle, as already reported for Neuro-2a cells, (Lebel et al 1994, Garcia-Silva et al 2002 rat chondrocyte primary culture (Ballock et al 2000), murine embryonic carcinoma P19 cells (Nygard et al 2003), and rat oligodendrocyte precursor cells (Tokumoto et al 1999). It is widely recognized that anti-proliferative agents can induce cell cycle perturbations associated with growth arrest (Otto et al 1996, Marchal et al 2004.…”

“…Numerous studies have shown that T 3 is able to promote or inhibit cell proliferation in a cell type-dependent manner (Ledda-Columbano et al 2005, Misiti et al 2005, Verga Falzacappa et al 2006. A thyroid hormone-mediated growth arrest has been observed in different cell lines including rat chondrocyte primary culture (Ballock et al 2000), murine neuroblastoma N2a-b cells that overexpress the thyroid hormone receptor b 1 isoform (Perez-Juste & Aranda 1999, Garcia-Silva et al 2002, murine embryonic carcinoma P19 cells (Nygard et al 2003), and rat oligodendrocyte precursor cells (Tokumoto et al 1999). An important report has demonstrated that cell proliferation induced by T 3 in rat liver is associated with nodule regression and reduction of hepatocellular carcinomas, therefore, this hormone exerts anti-carcinogenic effects in the liver also (Ledda-Columbano et al 2000).…”

BMP Signaling Mediates Astrocyte Differentiation of Oligodendrocyte Progenitor Cells

“…Total RNA from OPCs was extracted with the TRIzol (Invitrogen, Carlsbad, CA) according to the manufacturer's instructions. Two micrograms of total RNA were reverse transcribed to cDNA, and PCR was performed by a routine method (Tokumoto et al 1999). A negative control containing RNA instead of cDNA (without RT) was performed to rule out DNA contamination.…”