Slitrk Missense Mutations Associated with Neuropsychiatric Disorders Distinctively Impair Slitrk Trafficking and Synapse Formation.
Slit- and Trk-like (Slitrks) are a six-member family of synapse organizers that control excitatory and inhibitory synapse formation by formingtrans-synaptic adhesions with LAR receptor protein tyrosine phosphatases (PTPs). Intriguingly, genetic mutations of Slitrks have been associated with a multitude of neuropsychiatric disorders. However, nothing is known about the neuronal and synaptic consequences of these mutations. Here, we report the structural and functional effects on synapses of various rarede novomutations identified in patients with schizophrenia or Tourette syndrome. A number of single amino acid substitutions in Slitrk1 (N400I or T418S) or Slitrk4 (V206I or I578V) reduced their surface expression levels. These substitutions impaired glycosylation of Slitrks expressed in HEK293T cells, caused retention of Slitrks in the endoplasmic reticulum andcis-Golgi compartment in COS-7 cells and neurons, and abolished Slitrk binding to PTPδ. Furthermore, these substitutions eliminated the synapse-inducing activity of Slitrks, abolishing their functional effects on synapse density in cultured neurons. Strikingly, a valine-to-methionine mutation in Slitrk2 (V89M) compromised synapse formation activity in cultured neuron, without affecting surface transport, expression, or synapse-inducing activity in coculture assays. Similar deleterious effects were observed upon introduction of the corresponding valine-to-methionine mutation into Slitrk1 (V85M), suggesting that this conserved valine residue plays a key role in maintaining the synaptic functions of Slitrks. Collectively, these data indicate that inactivation of distinct cellular mechanisms caused by specific Slitrk dysfunctions may underlie Slitrk-associated neuropsychiatric disorders in humans, and provide a robust cellular readout for the development of knowledge-based therapies.
Department of Physiology and BK21 PLUS Project for Medical Science, Yonsei University College of Medicine Seoul, Korea.
Hyeyeon
H
Kang
Department of Physiology and BK21 PLUS Project for Medical Science, Yonsei University College of Medicine Seoul, Korea.
Kyung Ah
KA
Han
Department of Chemistry, Korea Advanced Institute of Science and Technology Daejeon, Korea.
Seoung Youn
SY
Won
Graduate School of Medical Science and Engineering, Korea Advanced Institute of Science and Technology Daejeon, Korea.
Ho Min
HM
Kim
Department of Physiology and BK21 PLUS Project for Medical Science, Yonsei University College of Medicine Seoul, Korea.
Young-Ho
YH
Lee
Department of Biochemistry, College of Life Science and Biotechnology, Yonsei University Seoul, Korea.
Jaewon
J
Ko
Department of Physiology and BK21 PLUS Project for Medical Science, Yonsei University College of Medicine Seoul, Korea.
Ji Won
JW
Um
Slitrks; Tourette’s Syndrome; schizophrenia; synapse formation; transmembrane protein