Glutamatergic cerebellar granule neurons synthesize and secrete reelin in vitro

Abstract

In the postnatal forebrain, the extracellular matrix protein reelin is expressed and secreted by subsets of GABAergic neurons, whereas in the cerebellum reelin is detected in glutamatergic cells of the granule cell layer. Thus, various regions of the postnatal brain present different patterns of reelin expression, whose significance remains unknown. We combined immunocytochemical and pharmacological approaches to characterize the phenotypic and temporal profiles of reelin expression in dissociated cultures of cerebellar granule neurons. A single type of reelin immunoreactivity, identified by a punctate labelling, was present in the somata of the majority of neurons. This immunoreactivity was observed throughout maturation and was exclusively present in glutamatergic neurons expressing the vesicular glutamate transporter 1. Neurons containing the reelin receptors apolipoprotein E receptor 2 (Apoer2) and very low-density lipoprotein receptor (Vldlr) represented about 80% of cerebellar neurons. The vast majority of reelin-positive neurons coexpressed Apoer2, suggesting that reelin immunoreactivity resulted in part from receptor-bound reelin. Inhibition of protein synthesis with cycloheximide completely abolished reelin immunoreactivity. In contrast, blocking protein secretion with brefeldin A did not affect the proportion of punctate neurons but revealed a subpopulation of neurons characterized by a solid reelin staining. These data show for the first time that a homogeneous population of glutamatergic neurons can synthesize and secrete reelin in cerebellar granule cells in vitro.

Reelin-mediated signaling in neuropsychiatric and neurodegenerative diseases

“…This neuronal activityindependent release of Reelin has also been described for cultured cerebellar granule cells (Lacor et al, 2000;Sinagra et al, 2008), as well as hippocampal neurons (Sinagra et al, 2005;Groc et al, 2007;Campo et al, 2009), revealing a tight relationship between synthesis and release rate, that was independent of depolarization-regulated Ca…”

Consensus Paper: Pathological Role of the Cerebellum in Autism

“…Reelin is an important protein expressed in GABAergic and glutamatergic cells [133, 134]. As a serine protease of the extracellular matrix, Reelin regulates proper lamination of neurons during embryonic development and helps in migration of neurons and maintenance of synaptic plasticity throughout life [135–137].…”

“…Among several mechanisms, this function also relies on a proteolytic activity exerted by reelin on extracellular matrix proteins, which is inhibited by organophosphate (OP) pesticides [134]. The PON1 gene encodes for a calcium-dependent enzyme frequently defined “paraoxonase”, which exerts several enzymatic activities including the inactivation of OPs, the degradation of lipid peroxides preventing atherosclerosis and vascular disease, the breakdown of bacterial endotoxins, and the prevention of protein lactonation [236].…”

Tipping the Balance of Autism Risk: Potential Mechanisms Linking Pesticides and Autism

“…The proteolytic activity of reelin on extracellular matrix proteins that control neuronal migration is significantly inhibited by OP pesticides (Sinagra et al 2008), and OP metabolism efficiency is regulated by the gene for paraoxonase 1 ( PON1 ) (Mackness et al 1997). Interestingly, an association between less active forms of the PON1 gene and autism was observed in Caucasian families in North America, but not in Italian families, leading authors to hypothesize that the slow metabolizing polymorphism confers risk in areas with high levels of OPs but may not affect autism risk otherwise (D’Amelio et al 2005).…”