Thyroid hormones (THs) regulate gene expression by binding to nuclear TH receptors (TRs) in the cell. THs are indispensable for brain development. However, we have little knowledge about how congenital hypothyroidism in neurons affects functions of the central nervous system in adulthood. Here, we report specific TH effects on functional development of the cerebellum by using transgenic mice overexpressing a dominant-negative TR (Mf-1) specifically in cerebellar Purkinje cells (PCs). Adult Mf-1 mice displayed impairments in motor coordination and motor learning. Surprisingly, long-term depression (LTD)–inductive stimulation caused long-term potentiation (LTP) at parallel fiber (PF)–PC synapses in adult Mf-1 mice, although there was no abnormality in morphology or basal properties of PF–PC synapses. The LTP phenotype was turned to LTD in Mf-1 mice when the inductive stimulation was applied in an extracellular high-Ca 2+ condition. Confocal calcium imaging revealed that dendritic Ca 2+ elevation evoked by LTD-inductive stimulation is significantly reduced in Mf-1 PCs but not by PC depolarization only. Single PC messenger RNA quantitative analysis showed reduced expression of SERCA2 and IP 3 receptor type 1 in Mf-1 PCs, which are essential for mGluR1-mediated internal calcium release from endoplasmic reticulum in cerebellar PCs. These abnormal changes were not observed in adult-onset PC-specific TH deficiency mice created by adeno-associated virus vectors. Thus, we propose the importance of TH action during neural development in establishing proper cerebellar function in adulthood, independent of its morphology. The present study gives insight into the cellular and molecular mechanisms underlying congenital hypothyroidism–induced dysfunctions of central nervous system and cerebellum.
The nuclear corepressor 1 (NCoR1) and the silencing mediator of retinoid and thyroid hormone receptors (SMRT) are critical coregulators of the thyroid hormone receptor (TR), mediating transcriptional repression via histone deacetylation. Thyroid hormone (TH) plays an essential role in many physiological processes via the TR. How the corepressors regulate TR signaling is not fully understood, especially in central nervous system (CNS). To determine the role of NCoR1 and SMRT in the CNS, we used mice with conditional NCoR1 (NCoR1lox/lox) and SMRT (SMRTlox/lox) alleles in combination with mice that express Cre recombinase in a neuronal specific fashion (Snap25-Cre). Global deletion of NCoR1 or SMRT during embryogenesis results in lethality. We also showed that NCoR1/SMRT double knock-out mice die within two weeks after induction of Cre activity in adult mice. Now, we found that neuronal specific NCoR1 or SMRT KO mice survive without obvious impairment of neuronal development. However, NCoR1/SMRT double knock-out mice die within postnatal 1-2 weeks and have impaired body growth. Thus, both NCoR1 and SMRT have important roles in maintaining normal neuronal function. Recently, cased of mutations in NCoR1 and SMRT in humans have been reported. These cases report phenotypes including Autism Spectrum Disorder (ASD) and intellectual disability. The cerebellum has been thought to contribute to motor control and learning. Surprisingly, it has also been shown to be a key brain structure involved in social cognition and its dysfunction may play a role in ASD. The Purkinje cell is the main neuron in the cerebellum. Thus, we generated cerebellar Purkinje cell specific NCoR1/SMRT knock-out mice using L7/Pcp2-Cre mice. In contrast to neuronal specific KO mice, both NCoR1 or SMRT single or double knock-out mice survive until adulthood. SMRT Purkinje cell knock-out mice showed abnormalities in 3ch social interaction test indicating impaired social functioning, similar to some ASD symptoms. Electrophysiological testing showed current injection evoked more action potentials in SMRT KO mice. These results suggest Purkinje cell dysfunction caused by SMRT deletion may result in social disability. Our data demonstrate for the first time that NCoR1 and SMRT have separate functions in different areas of the brain but also have some redundant function when knocked out together in all neurons.
Thyroid hormone (TH) is essential for the development and the maintenance of the brain function. TH action is mediated by TH receptor (TR). TR binds to a specific DNA sequence on TH-target genes and thus functions as a ligand-dependent transcription factor. In thyroid diseases such as congenital hypothyroidism or resistance to TH (RTH), TH-TR binding is dominantly disrupted, leading to the various symptoms such as motor deficits. However, in such cases, all the cells that express TR get affected by the disrupted TR signaling; thus, the specific mechanism has not been cleared. It has been well known that proper motor coordination is deeply related to long term depression (LTD) of synaptic transmission from parallel fiber (PF) to Purkinje cell (PC) in the cerebellum (Ito, 1989). Therefore, we examined the involvement of TR in synaptic plasticity at PF-PC synapses by using transgenic mice (Mf-1 mice) which express dominant-negative TR specifically in PCs. Since Mf-1 display the impairment of motor coordination and motor learning, a decrease in TR signaling in PCs may alter synaptic plasticity and contribute to motor incoordination. A whole-cell patch clamp recording of Mf-1 PCs revealed the inhibition of LTD but instead the induction of long term potentiation (LTP) of the synaptic transmission at PF-PC synapses. This indicates that the intracellular calcium dynamics may be disrupted in Mf-1 PCs since LTD requires a higher elevation of the intracellular calcium concentration in PCs than LTP does. Indeed, single-PC qPCR showed that the mRNA levels of some important molecules for the intracellular calcium dynamics in PCs (SERCA2, IP3R, and P/Q-type calcium channel) are downregulated in Mf-1 PCs. This result suggests those genes as possible TH-target genes. Taken together, the present study suggested a novel possible role of TR in synaptic plasticity at PF-PC synapses by regulating the expression of some important genes for LTD occurrence in the cerebellum. This finding could give a new insight into the mechanism of motor deficits in thyroid diseases.
The nuclear receptor corepressor 1 (NCoR1) and the silencing mediator of retinoic acid and thyroid hormone (SMRT) are critical coregulators of the nuclear receptor (e.g., thyroid hormone receptors and retinoic acid receptors), mediating transcriptional repression via histone deacetylation. Although they are highly homologous and have similar nuclear receptor interaction domains, they have different roles in different organs. Recently, de novo genetic variants in nuclear corepressors were found in pediatric patients with neurodevelopmental disorders. Thus, we generated the mouse models to understand the role of NCOR1 and SMRT in the central nervous system. We used the mice with conditional NCoR1 or SMRT (NCoR1lox/lox or SMRTlox/lox) alleles in combination with the mice that express Cre recombinase in a neuronal specific fashion (Snap25-Ires2-Cre). First, we performed a battery of behavioral tests to screen behavioral phenotype of mice. We found that hypoactivity, social deficits, and mild anxiety in neuronal specific NCoR1 or SMRT KO mice. In addition, NCoR1 KO mice showed high learning abilities in pairwise visual discrimination task. Next, we performed RNA-sequencing analysis with amygdala from postnatal day 21 to investigate gene expression mediated by NCoR1 and SMRT. We found that 449 genes were upregulated by SMRT deletion, whereas only 8 genes were upregulated by NCoR1 deletion. Overall, our data demonstrate for the first time that NCoR1 and SMRT have separate functions in the central nervous system. JSPS Grant-in-Aid for Early-Career Scientists 19K16486, 21K15340 This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.
It has been reported that the exposure to environmental chemicals including endocrine-disrupting chemicals in early life can cause developmental diseases in children. We previously reported that the lactational exposure to perfluorooctane sulfonate (PFOS) caused the impairment in the cognitive and motor functions in adult male mice. However, little is known how the early-life PFOS exposure affects such brain functions in aged subjects. The present study investigated the prolonged effects of PFOS on cognitive function, anxiety, and social behavior using aged male mice (> 365 postnatal day). Mice were exposed to PFOS (1 mg / kg body weight) during the lactational period. In the visual discrimination test, both control and PFOS groups showed a decrease in the learning curve. There is no difference in % correct between groups. In the object location test, there were no changes in both short- and long-term memory. In the object recognition test, long-term memory was attenuated in the PFOS group. The test battery for anxiety (elevated-plus maze test, light and dark chamber test, marble burying test) detected no difference between groups. In the three-chamber social interaction test, PFOS-exposed mice showed an avoidance to interact with a novel mouse, which was not observed during the young-adult period. These results indicate that the PFOS mainly affects social activity during aging. Nothing to disclose This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.
Perfluorooctane sulfonate (PFOS) has been used in a wide variety of industrial and commercial products. The adverse effects of PFOS on the developing brain are becoming of a great concern. However, the molecular mechanisms of PFOS on brain development have not yet been clarified. We investigated the effect of early-life exposure to PFOS on brain development and the mechanism involved. We investigated the change in thyroid hormone (TH)-induced dendrite arborization of Purkinje cells in the primary culture of newborn rat cerebellum. We further examined the mechanism of PFOS on TH signaling by reporter gene assay, quantitative RT-PCR, and type 2 iodothyronine deiodinase (D2) assay. As low as 10−7 M PFOS suppressed thyroxine (T4)-, but not triiodothyronine (T3)-induced dendrite arborization of Purkinje cells. Reporter gene assay showed that PFOS did not affect TRα1- and TRβ1-mediated transcription in CV-1 cells. RT-PCR showed that PFOS suppressed D2 mRNA expression in the absence of T4 in primary cerebellar cells. D2 activity was also suppressed by PFOS in C6 glioma-derived cells. These results indicate that early-life exposure of PFOS disrupts TH-mediated cerebellar development possibly through the disruption of D2 activity and/or mRNA expression, which may cause cerebellar dysfunction.
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