Nuclear Receptor Corepressors NCoR1 and SMRT Plays Unique Roles in Central Nervous System

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 (NCoR1(lox/lox)) and SMRT (SMRT(lox/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.