Secreted Metalloproteinase ADAMTS-3 Inactivates Reelin

Abstract

The secreted glycoprotein Reelin regulates embryonic brain development and adult brain functions. It has been suggested that reduced Reelin activity contributes to the pathogenesis of several neuropsychiatric and neurodegenerative disorders, such as schizophrenia and Alzheimer's disease; however, noninvasive methods that can upregulate Reelin activity have yet to be developed. We previously found that the proteolytic cleavage of Reelin within Reelin repeat 3 (N-t site) abolishes Reelin activity, but it remains controversial as to whether this effect occurs Here we partially purified the enzyme that mediates the N-t cleavage of Reelin from the culture supernatant of cerebral cortical neurons. This enzyme was identified as a disintegrin and metalloproteinase with thrombospondin motifs-3 (ADAMTS-3). Recombinant ADAMTS-3 cleaved Reelin at the N-t site. ADAMTS-3 was expressed in excitatory neurons in the cerebral cortex and hippocampus. N-t cleavage of Reelin was markedly decreased in the embryonic cerebral cortex of ADAMTS-3 knock-out (KO) mice. Importantly, the amount of Dab1 and the phosphorylation level of Tau, which inversely correlate with Reelin activity, were significantly decreased in the cerebral cortex of ADAMTS-3 KO mice. Conditional KO mice, in which ADAMTS-3 was deficient only in the excitatory neurons of the forebrain, showed increased dendritic branching and elongation in the postnatal cerebral cortex. Our study shows that ADAMTS-3 is the major enzyme that cleaves and inactivates Reelin in the cerebral cortex and hippocampus. Therefore, inhibition of ADAMTS-3 may be an effective treatment for neuropsychiatric and neurodegenerative disorders. ADAMTS-3 was identified as the protease that cleaves and inactivates Reelin in the cerebral cortex and hippocampus. ADAMTS-3 was expressed in the excitatory neurons of the embryonic and postnatal cerebral cortex and hippocampus. Cleavage by ADAMTS-3 is the major contributor of Reelin inactivation Tau phosphorylation was decreased and dendritic branching and elongation was increased in ADAMTS-3-deficient mice. Therefore, inhibition of ADAMTS-3 upregulates Reelin activity and may be a potential therapeutic strategy for the prevention or treatment of neuropsychiatric and neurodegenerative disorders, such as schizophrenia and Alzheimer's disease.

Physiological significance of proteolytic processing of Reelin revealed by cleavage-resistant Reelin knock-in mice

“…This may explain why the level of Tau phosphorylation in the embryonic cerebral cortex, which was markedly down-regulated in ADAMTS-3 KO mice 12 , was not significantly affected in KI/KI mice (Fig. 1E).…”

“…However, ADAMTS-3 was not the only protease to inactivate Reelin; its cleavage still occurred in the cerebral cortex and hippocampus of 3 ADAMTS-3 KO mice 12 . The neuronal dendrites contained more branches and were elongated in the cerebral cortex of ADAMTS-3 conditional KO mice compared to the control mice 12 . We speculated that this effect was due to decreased Reelin cleavage, but it remained possible that there was a critical ADAMTS-3 substrate(s) that somehow affected dendrite morphology.…”

“…Phosphorylated Dab1 is quickly degraded 1,2,5 . Thus, the amount of Dab1 is indicative of the strength of Reelin signaling [12][13][14][15] . Several pathways act downstream of Dab1 phosphorylation and regulate the cytoskeleton, adhesion molecules, ion channels, and neurotransmitter release [1][2][3]5,16 .…”

“…We recently identified ADAMTS-3 (a disintegrin and metalloproteinase with thrombospondin motifs 3) as the major protease that mediates N-t cleavage in the embryonic and early postnatal cerebral cortex and hippocampus 12 . More importantly, the results from ADAMTS-3 knock-out (KO) mice indicated that N-t cleavage is the primary mechanism of Reelin inactivation in these tissues 12 . However, ADAMTS-3 was not the only protease to inactivate Reelin; its cleavage still occurred in the cerebral cortex and hippocampus of 3 ADAMTS-3 KO mice 12 .…”

“…More importantly, the results from ADAMTS-3 knock-out (KO) mice indicated that N-t cleavage is the primary mechanism of Reelin inactivation in these tissues 12 . However, ADAMTS-3 was not the only protease to inactivate Reelin; its cleavage still occurred in the cerebral cortex and hippocampus of 3 ADAMTS-3 KO mice 12 . The neuronal dendrites contained more branches and were elongated in the cerebral cortex of ADAMTS-3 conditional KO mice compared to the control mice 12 .…”