Thyrotropin-Releasing-Hormone-Synthesizing Neurons of the Hypothalamic Paraventricular Nucleus Are Inhibited by Glycinergic Inputs.

Background: Glycine is a classical neurotransmitter that has role in both inhibitory and excitatory synapses. To understand whether glycinergic inputs are involved in the regulation of the hypophysiotropic thyrotropin-releasing hormone (TRH) neurons, the central controllers of the hypothalamic-pituitary-thyroid axis, the glycinergic innervation of the TRH neurons was studied in the hypothalamic paraventricular nucleus (PVN). Methods: Double-labeling immunocytochemistry and patch-clamp electrophysiology were used to determine the role of glycinergic neurons in the regulation of TRH neurons in the PVN. Anterograde and retrograde tracing methods were used to determine the sources of the glycinergic input of TRH neurons. Results: Glycine transporter-2 (GLYT2), a marker of glycinergic neurons, containing axons were found to establish symmetric type of synapses on TRH neurons in the PVN. Furthermore, glycine receptor immunoreactivity was observed in these TRH neurons. The raphe magnus (RMg) and the ventrolateral periaqueductal gray (VLPAG) were found to be the exclusive sources of the glycinergic innervation of the TRH neurons within the PVN. Patch-clamp electrophysiology using sections of TRH-IRES-tdTomato mice showed that glycine hyperpolarized the TRH neurons and completely blocked the firing of these neurons. Glycine also markedly hyperpolarized the TRH neurons in the presence of tetrodotoxin demonstrating the direct effect of glycine. In more than 60% of the TRH neurons, spontaneous inhibitory postsynaptic currents (sIPSCs) were observed, even after the pharmacological inhibition of glutamatergic and GABAergic neuronal transmission. The glycine antagonist, strychnine, almost completely abolished these sIPSCs, demonstrating the inhibitory nature of the glycinergic input of TRH neurons. Conclusions: These data demonstrate that TRH neurons in the PVN receive glycinergic inputs from the RMg and the VLPAG. The symmetric type of synaptic connection and the results of the electrophysiological experiments demonstrate the inhibitory nature of these inputs.

Type 2 deiodinase polymorphism causes ER stress and hypothyroidism in the brain.

Levothyroxine (LT4) is a form of thyroid hormone used to treat hypothyroidism. In the brain, T4 is converted to the active form T3 by type 2 deiodinase (D2). Thus, it is intriguing that carriers of the Thr92Ala polymorphism in the D2 gene (DIO2) exhibit clinical improvement when liothyronine (LT3) is added to LT4 therapy. Here, we report that D2 is a cargo protein in ER Golgi intermediary compartment (ERGIC) vesicles, recycling between ER and Golgi. The Thr92-to-Ala substitution (Ala92-D2) caused ER stress and activated the unfolded protein response (UPR). Ala92-D2 accumulated in the trans-Golgi and generated less T3, which was restored by eliminating ER stress with the chemical chaperone 4-phenyl butyric acid (4-PBA). An Ala92-Dio2 polymorphism-carrying mouse exhibited UPR and hypothyroidism in distinct brain areas. The mouse refrained from physical activity, slept more, and required additional time to memorize objects. Enhancing T3 signaling in the brain with LT3 improved cognition, whereas restoring proteostasis with 4-PBA eliminated the Ala92-Dio2 phenotype. In contrast, primary hypothyroidism intensified the Ala92-Dio2 phenotype, with only partial response to LT4 therapy. Disruption of cellular proteostasis and reduced Ala92-D2 activity may explain the failure of LT4 therapy in carriers of Thr92Ala-DIO2.

Does borderline kidney allograft rejection always require treatment?

BACKGROUND: Borderline rejection (Bord-R) is a frequent diagnosis in renal transplantation, and there is increasing evidence that regulatory T lymphocytes are involved in its pathogenesis. Current histopathologic practice does not differentiate between graft-protecting and -damaging T lymphocytes, and patients with Bord-R routinely receive rejection treatment. We analyzed Treg-associated forkhead box P3 (Foxp3) gene expression in Bord-R and more severe forms of acute rejection episodes (ARE). METHODS: Foxp3 transcripts were measured in 520 serial peripheral blood samples from 177 kidney graft recipients obtained during the first 20 days posttransplantation. RESULTS: The highest Foxp3 transcripts were observed in patients with Bord-R or without rejection and the lowest in patients with ARE. Patients with Bord-R on posttransplant days 5 to 7 showed an increased Foxp3 transcript level of 156%, which increased to 302% by posttransplant days 14 to 16. In contrast, patients with ARE demonstrated significantly lower Foxp3 gene expression than that observed in Bord-R, nonrejectors, or acute tubular necrosis patients (P=0.001, P<0.001, and P=0.005, respectively, on days 11-13). Acute tubular necrosis patients demonstrated intermediately high Foxp3 gene expression. CONCLUSIONS: Our data indicate that increased Treg activity in peripheral blood is a frequent feature of Bord-R. This finding questions the appropriateness of rejection treatment in all patients with the histopathologic diagnosis "Bord-R".