Mmp1 processing of the PDF neuropeptide regulates circadian structural plasticity of pacemaker neurons.

In the Drosophila brain, the neuropeptide PIGMENT DISPERSING FACTOR (PDF) is expressed in the small and large Lateral ventral neurons (LNvs) and regulates circadian locomotor behavior. Interestingly, PDF immunoreactivity at the dorsal terminals changes across the day as synaptic contacts do as a result of a remarkable remodeling of sLNv projections. Despite the relevance of this phenomenon to circuit plasticity and behavior, the underlying mechanisms remain poorly understood. In this work we provide evidence that PDF along with matrix metalloproteinases (Mmp1 and 2) are key in the control of circadian structural remodeling. Adult-specific downregulation of PDF levels per se hampers circadian axonal remodeling, as it does altering Mmp1 or Mmp2 levels within PDF neurons post-developmentally. However, only Mmp1 affects PDF immunoreactivity at the dorsal terminals and exerts a clear effect on overt behavior. In vitro analysis demonstrated that PDF is hydrolyzed by Mmp1, thereby suggesting that Mmp1 could directly terminate its biological activity. These data demonstrate that Mmp1 modulates PDF processing, which leads to daily structural remodeling and circadian behavior.

Amyloid peptides ABri and ADan show differential neurotoxicity in transgenic Drosophila models of familial British and Danish dementia.

BACKGROUND: Familial British and Familial Danish dementias (FBD and FDD, respectively) are associated with mutations in the BRI2 gene. Processing of the mutated BRI2 protein leads to the accumulation in the brain of the 34-mer amyloid Bri (ABri) and amyloid Dan (ADan) peptides, accompanied by neurofibrillary tangles. Recently, transgenic mice successfully reproduced different aspects of FDD, while modeling of FBD in vivo has been more difficult. In this work we have modeled FBD and FDD in Drosophila and tested the hypothesis that ABri and ADan are differentially neurotoxic. RESULTS: By using site-directed insertion, we generated transgenic lines carrying ABri, ADan, Bri2-23 (the normal product of wild-type BRI2 processing) and amyloid-ß (Aß) 1-42 as a well-characterized neurotoxic peptide, alone or with a His-tag. Therefore, we avoided random insertion effects and were able to compare levels of accumulation accurately. Peptides were expressed with the GAL4-Upstream Activating Sequence (UAS) system using specific drivers. Despite low levels of expression, toxicity in the eye was characterized by mild disorganization of ommatidia and amyloid peptides accumulation. The highest toxicity was seen for ADan, followed by Aß42 and ABri. Pan-neuronal expression in the CNS revealed an age-dependent toxicity of amyloid peptides as determined by the ability of flies to climb in a geotaxis paradigm when compared to Bri2-23. This effect was stronger for ADan, detected at 7 days post-eclosion, and followed by ABri and Aß42, whose toxicity became evident after 15 and 21 days, respectively. Histological analysis showed mild vacuolization and thioflavine-S-negative deposits of amyloid peptides. In contrast, the over-expression of amyloid peptides in the specific subset of lateral neurons that control circadian locomotor activity showed no toxicity. CONCLUSIONS: Our results support the differential neurotoxicity of ADan and ABri in the Drosophila eye and CNS at low expression levels. Such differences may be partially attributed to rates of aggregation and accumulation. In the CNS, both peptides appear to be more neurotoxic than wild-type Aß42. These Drosophila models will allow a systematic and unambiguous comparison of differences and similarities in the mechanisms of toxicity of diverse amyloid peptides associated with dementia.

Collapsin response mediator protein-2 phosphorylation promotes the reversible retraction of oligodendrocyte processes in response to non-lethal oxidative stress.

The extension of processes of oligodendrocyte (OLG) and their precursor cells are crucial for migration, axonal contact and myelination. Here we show that a non-lethal oxidative stress induced by 3-nitropropionic acid (3-NP) elicited a rapid shortening of processes (~24%) in primary OLGs and in oligodendroglial cell line (OLN-93) cells (~36%) as compared with vehicle-exposed cells. This was reversible and prevented by antioxidants. Proteomics of OLG lysates with and without 3-NP treatment yielded collapsin response mediator protein 2 (CRMP-2) as a candidate effector molecule. Inhibition of rho kinase was sufficient to prevent process retraction in both OLGs and OLN-93 cells. Oxidative stress increased phosphorylation of CRMP-2 at T555 that was completely prevented by Y27632. Moreover, transfection of OLN-93 cells with the mutant CRMP-2 T555A which cannot be phosphorylated by rho kinase, prevented process shortening induced by 3-NP as compared with wild-type CRMP-2. Our results suggest a role for endogenous reactive oxygen species in a pathway that regulates OLG process extension. The vulnerability of late myelinated neurons in the adult brain and the presence of white matter pathology in human dementias warrant the study of this oligodendroglial pathway in the early stages of neurodegenerative conditions characterized by oxidative stress.

[Cerebral proteolysis of amiloid-b peptide: relevance of insulin-degrading enzyme in Alzheimer's disease]. / Proteólisis cerebral del peptido amiloide-b: Relevancia de la enzima degradadora de insulina en la enfermedad de Alzheimer.

The global increase in life expectancy turns Alzheimer's disease (AD) into a growing problem. One of the distinctive features of AD is the excessive accumulation of amyloid-b (Ab) peptide in the brain. In recent years, a concept that has gained strength is that degradation of Ab by proteases in situ is an important mechanism that prevents cerebral peptide accumulation. Biochemical and genetic data have shown that insulin-degrading enzyme (IDE) participates in Ab and insulin homeostasis. IDE expression and activity are significantly decreased in AD brains compared to age-matched controls. Also, IDE is deposited with Ab in senile plaques and blood vessels, indicating a gross conformational change as a consequence of diverse post-translational mechanisms. These alterations in IDE distribution and activity may result in insufficient degradation of Ab and insulin, promoting the formation of Ab oligomers and hormone resistance. Both processes might play a fundamental part in neurodegeneration. The study of the clearance mechanisms of cerebral Ab will not only aid in the understanding AD pathogenesis but will also allow a better interpretation of ongoing clinical trials and the development of new therapeutic strategies.