Intracellular and plasma membrane-initiated pathways involved in the [Ca²⁺]_ielevations induced by iodothyronines (T3 and T2) in pituitary GH₃cells

Abstract

]i increases induced by T2 and T3. In the presence of extracellular calcium (1.2 mM), under carbonyl cyanide 4-(trifluoromethoxy)phenylhydrazone, T2 and T3 increased both [Ca 2ϩ ]i and intracellular Na ϩ concentration; nimodipine reduced the [Ca 2ϩ ]i increases elicited by T2 and T3, but inhibition of NO synthase and blockade of the Na ϩ /H ϩ pump by 5-(N-ethyl-N-isopropyl)amiloride prevented only that elicited by T3; and CB-DMB, bisindolylmaleimide, and LY-294002 (inhibitors of the Na ϩ /Ca 2ϩ exchanger, PKC, and phosphatidylinositol 3-kinase, respectively) failed to modify the T2-and T3-induced effects. Collectively, the present results suggest that T2 and T3 exert short-term nongenomic effects on intracellular calcium and NO by modulating plasma membrane and mitochondrial pathways that differ between these iodothyronines. thyroid hormones; mitochondria; calcium; nitric oxide THYROID HORMONES (thyroxine, T4; triiodothyronine, T3) play important roles in cellular development, growth, and metabolism, mainly through the interaction of T3 with nuclear receptors (38). In addition, short-term, nongenomic actions of thyroid hormones have been reported to occur at the level of the plasma membrane, channels and pumps, cytoskeleton, cytoplasm, and organelles in mammalian cells (for review, see Ref. 16 and references therein) (15,17,33,48,51). Some of these actions lead rapidly to posttranslational modifications of nucleoproteins, including MAPK-mediated serine phosphorylation of the thyroid hormone receptor (13), estrogen receptor (52), and p53 (49). In addition, upstream of MAPK, PKC and phosphatidylinositol 3-kinase (PI3-K) pathways may also be activated by thyroid hormones (42).These rapid events seem to imply the existence of membrane receptors for thyroid hormones linked to signal-transduction pathways that are not yet well characterized. Indeed, membrane binding sites for T3 have been identified in human and rat erythrocytes (9, 2), rat hepatocytes (28, 40), and pituitary cells (25), and Bergh and colleagues (7) have identified integrin-␣V␤3 as a plasma membrane thyroid hormone binding site.In addition to T3, other iodothyronines, such as 3,5-diiodo-L-thyronine (T2), a naturally occurring iodothyronine, display biological activities. Indeed, it has been shown that T2 exerts short-term effects on both resting metabolic rate and mitochondrial activities (29), essentially by a nuclearindependent pathway (for review, see Ref. 35 and references therein). In previous studies, it has been suggested that T2, as well as T3, may influence cellular energy metabolism and cell differentiation by modulating ion pathways (27,36,47). In particular, T3 can induce a redistribution of calcium across plasma and mitochondrial membranes, thereby affecting energy metabolism (27,36). Although a role for calcium has been proposed in the mediation of the nongenomic effects triggered by iodothyronines, the underlying biochemical pathways are not yet fully established.In the present study, in pituitary GH 3 cells, we explored 1) the modu...

3,5,3′-Triiodo-L-Thyronine- and 3,5-Diiodo-L-Thyronine- Affected Metabolic Pathways in Liver of LDL Receptor Deficient Mice

“…The reduction in the expression levels of lactoylglutathione lyase and aldehyde dehydrogenase, on the other hand, indicates a lower content of detoxifying enzymes in the liver of Ldlr −/− mice treated with either T2 or T3. Of note, consistent with what was previously reported (Silvestri et al, 2006), we observed an iodothyronine-induced decrease of the hepatic level of regucalcin, suggesting a role of calcium availability in the cellular effects of T2 and T3 (Del Viscovo et al, 2012). …”

Hippocampal Gene Expression of Deiodinases 2 and 3 and Effects of 3,5-Diiodo-L-Thyronine T2 in Mouse Depression Paradigms

“…A hypothesis was derived for the mechanism of the transport of thyroid hormones from the bloodstream to the brain involving thyroid hormone transporter synthesized in choroid plexus and secreted into the cerebrospinal fluid [49]. While several mechanisms of action of T2 can be proposed, including above-discussed effects of this hormone on monoamine and integrin receptors, PI3 K-Akt signaling and TRH, given accumulated evidences concerning eminent effects of T2 on the mitochondrial respiratory chain [20, 21], biogenesis [17], and calcium and NO signalling [22], they are likely to be due to the enhancement of mitochondrial functions, a validated target of antidepressant therapy [19]. …”

“…Unlike T3, T2 enhances mitochondrial respiration by a nuclear-independent mechanism and neither does act via thyroid hormone receptor beta, nor via AMP-activated protein kinase. T2 was demonstrated to activate reactions involved in substrate oxidation, affecting both cytochrome c reducers and cytochrome c oxidizers [20, 21], and besides it effects on respiratory chain, it was suggested to increase the downstream mechanisms that are involved in mitochondrial biogenesis [17]; these and other effects of T2 on mitochondrial pathways were shown to be distinct from the effects of T3 [22]. In contrast to the lasting l effects of T3 on metabolic rate and mitochondrial respiration, with onset delayed for 48 h, the action of T2 appears within the first few hours and does not persist for longer than 48 h and is not sensitive to actinomycin D [5, 20, 22].…”

Polychlorinated Biphenyls Induce Mitochondrial Dysfunction in SH-SY5Y Neuroblastoma Cells

“…After the incubation with A1254, A1254+ pyruvic acid, and pyruvic acid alone, cells were loaded with 10 μM 4,5-diaminofluorescein-2-diacetate (DAF-2DA) in a humidified 5% CO 2 atmosphere at 37°C for 30 min [ 20 ]. For control experiments, cells were incubated only in normal Krebs solution.…”