Targeted deletion of betaIII spectrin impairs synaptogenesis and generates ataxic and seizure phenotypes.

Abstract

The spectrin membrane skeleton controls the disposition of selected membrane channels, receptors, and transporters. In the brain betaIII spectrin binds directly to the excitatory amino acid transporter (EAAT4), the glutamate receptor delta, and other proteins. Mutations in betaIII spectrin link strongly to human spinocerebellar ataxia type 5 (SCA5), correlating with alterations in EAAT4. We have explored the mechanistic basis of this phenotype by targeted gene disruption of Spnb3. Mice lacking intact betaIII spectrin develop normally. By 6 months they display a mild nonprogressive ataxia. By 1 year most Spnb3(-/-) animals develop a myoclonic seizure disorder with significant reductions of EAAT4, EAAT1, GluRdelta, IP3R, and NCAM140. Other synaptic proteins are normal. The cerebellum displays increased dark Purkinje cells (PC), a thin molecular layer, fewer synapses, a loss of dendritic spines, and a 2-fold expansion of the PC dendrite diameter. Membrane and expanded Golgi profiles fill the PC dendrite and soma, and both regions accumulate EAAT4. Correlating with the seizure disorder are enhanced hippocampal levels of neuropeptide Y and EAAT3 and increased calpain proteolysis of alphaII spectrin. It appears that betaIII spectrin disruption impairs synaptogenesis by disturbing the intracellular pathways selectively regulating protein trafficking to the synapse. The mislocalization of these proteins secondarily disrupts glutamate transport dynamics, leading to seizures, neuronal damage, and compensatory changes in EAAT3 and neuropeptide Y.

• Authors: Michael C Stankewich, Babette Gwynn, Thomas Ardito, Lan Ji, Jung Kim, Raymond F Robledo, Samuel E Lux, Luanne L Peters, Jon S Morrow
• Journal: Proceedings of the National Academy of Sciences of the United States of America (Proc Natl Acad Sci U S A) Vol. 107 Issue 13 Pg. 6022-7 (Mar 30 2010) ISSN: 1091-6490 [Electronic] United States
• PMID: 20231455 (Publication Type: Journal Article, Research Support, N.I.H., Extramural)

Chemical References

• DNA Primers
• Excitatory Amino Acid Transporter 4
• Slc1a6 protein, mouse
• Spectrin

Topics

• Animals
• Ataxia (etiology, genetics, physiopathology)
• Base Sequence
• Brain (metabolism, physiopathology, ultrastructure)
• DNA Primers (genetics)
• Disease Models, Animal
• Excitatory Amino Acid Transporter 4 (metabolism)
• Female
• Gene Targeting
• Humans
• Male
• Mice
• Mice, Inbred C57BL
• Mice, Knockout
• Microscopy, Electron, Transmission
• Nerve Degeneration (genetics, physiopathology)
• Phenotype
• Seizures (etiology, genetics, physiopathology)
• Spectrin (deficiency, genetics, physiology)
• Spinocerebellar Ataxias (etiology, genetics, physiopathology)
• Synapses (physiology, ultrastructure)