Tri-iodothyronine inhibits multilayer formation of the osteoblastic cell line, MC3T3-E1, by promoting apoptosis

Abstract

Cell death through apoptosis is a well-known mechanism for maintaining homoeostasis in many developmental and pathological processes. We have recently presented evidence for the occurrence of apoptosis during the formation of bone-like tissue in vitro. MC3T3-E1 osteoblast-like cells in culture develop features of the osteoblastic phenotype and form many cell layers embedded in extracellular matrix which can mineralise. Tri-iodothyronine (T 3 ), even though it enhances the expression of many osteoblastic features, attenuates the multilayer formation to about two layers. The aim of this study was to investigate how T 3 prevents multilayer formation. MC3T3-E1 cells were seeded at different densities and cultured for up to 2 weeks. Thereafter we analysed proliferation rate and the distribution of the phases of the cell cycle and studied apoptosis. We found that T 3 did not inhibit DNA synthesis. Analysis of the cell cycle phases showed an increase in the number of cells in G0/G1 with increasing cell density, but no significant effect of T 3 treatment was found. Morphological investigations showed apoptotic features in both cell layers and culture supernatants. The cells exhibited typical plasma membrane blebbings, chromatin condensation, DNA fragmentation and phagocytosed apoptotic bodies. T 3 treatment significantly increased the number of apoptotic cells. We conclude from our data that T 3 inhibits multilayer formation of MC3T3-E1 cells by increasing the rate of apoptosis and not by inhibition of proliferation. Because apoptosis is a fundamental regulatory event during bone tissue differentiation, our findings emphasise the importance of thyroid hormones in bone maintenance and development.

1,25-Dihydroxyvitamin D3 inhibits thyroid hormone-induced osteocalcin expression in mouse osteoblast-like cells via a thyroid hormone response element

“…This stimulation is time-and dose-dependent and depends on the cell density (Varga et al 1997(Varga et al , 1999. The basal expression is inhibited by 1,25D3 (Zhang et al 1997) and both this inhibition and the stimulation by T3 was transmitted to the protein level (Fig.…”

Fluid shear stress inhibits TNF‐α‐induced apoptosis in osteoblasts: A role for fluid shear stress‐induced activation of PI3‐kinase and inhibition of caspase‐3

“…Regulation of cell survival is a complex process involving multiple extracellular factors and intracellular signaling pathways (Fratzl-Zelman et al, 1997;Globus et al, 1998;Lynch et al, 1998;Varga et al, 1999;Adams et al, 2001). How each of these factors affect the regulation of osteoblast apoptosis in vivo remains to be determined.…”

Regulation of Microglial Development: A Novel Role for Thyroid Hormone

“…This contrasts with the death-promoting effect of T3 on other mesodermal derivatives, including erythrocytic progenitors and osteoblastic and promyeloleukemic cells (Gandrillon et al, 1994;Suzuki et al, 1997;Varga et al, 1999), or the lack of direct influence of T3 on the survival of oligodendrocytes and their precursors (Rodríguez-Peña, 1999). However, T3 also directly supports survival of neuronal subpopulations (Filipcik et al, 1994;Muller et al, 1995).…”