Further Studies on the Role of BTBD9 in the Cerebellum, Sleep-like Behaviors and the Restless Legs Syndrome

• Published in: Neuroscience 2022-11, Vol.505, p.78-90
• Main Authors: Lyu, Shangru, Xing, Hong, Liu, Yuning, Girdhar, Pallavi, Yokoi, Fumiaki, Li, Yuqing
• Format: Article
• Language: English
• Subjects: Animals; BK channels; Btbd9; cerebellar Purkinje cells; Cerebellum - metabolism; Mice; Mice, Knockout; Nerve Tissue Proteins - metabolism; Psychomotor Agitation; ras GTPase-Activating Proteins - metabolism; restless legs syndrome; Restless Legs Syndrome - genetics; Restless Legs Syndrome - metabolism; SK channels; Sleep; SYNGAP1
• ISSN: 0306-4522; 1873-7544
• DOI: 10.1016/j.neuroscience.2022.10.008

•Increased BK but decreased SK currents, and enhanced AHP in PCs of Btbd9 KO mice.•Increased BK channel protein levels in the cerebellum of Btbd9 KO mice.•SYNGAP1 protein level decreased in Btbd9 KO mice due to its interaction with BTBD9.•Syngap1−/+ mice did not have restless legs syndrome-like diurnal motor restlessness.•Btbd9 PC-specific KO developed motor coordination and balance deficits as Btbd9 KO. Genetic analyses have linked BTBD9 to restless legs syndrome (RLS) and sleep regulation. Btbd9 knockout mice show RLS-like motor restlessness. Previously, we found hyperactivity of cerebellar Purkinje cells (PCs) in Btbd9 knockout mice, which may contribute to the motor restlessness observed. However, underlying mechanisms for PC hyperactivity in Btbd9 knockout mice are unknown. Here, we used dissociated PC recording, brain slice recording and western blot to address this question. Our dissociated recording shows that knockout PCs had increased TEA-sensitive, Ca2+-dependent K+ currents. Applying antagonist to large conductance Ca2+-activated K+ (BK) channels further isolated the increased current as BK current. Consistently, we found increased amplitude of afterhyperpolarization and elevated BK protein levels in the knockout mice. Dissociated recording also shows a decrease in TEA-insensitive, Ca2+-dependent K+ currents. The result is consistent with reduced amplitude of tail currents, mainly composed of small conductance Ca2+-activated K+ (SK) currents, in slice recording. Our results suggest that BK and SK channels may be responsible for the hyperactivity of knockout PCs. Recently, BTBD9 protein was shown to associate with SYNGAP1 protein. We found a decreased cerebellar level of SYNGAP1 in Btbd9 knockout mice. However, Syngap1 heterozygous knockout mice showed nocturnal, instead of diurnal, motor restlessness. Our results suggest that SYNGAP1 deficiency may not contribute directly to the RLS-like motor restlessness observed in Btbd9 knockout mice. Finally, we found that PC-specific Btbd9 knockout mice exhibited deficits in motor coordination and balance similar to Btbd9 knockout mice, suggesting that the motor effect of BTBD9 in PCs is cell-autonomous.