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GSK-3 in neuronal plasticity and neurodegeneration: basic mechanisms and pre-clinical assessment.

Final Report Summary - NEURO.GSK3 (GSK-3 in neuronal plasticity and neurodegeneration: basic mechanisms and pre-clinical assessment)

Executive summary:
Neuronal circuits depend for transmission of information on the polarised distribution, rapid movement and re-organisation of receptors, enzymes and vesicles in synapses, axons and dendrites. Protein complexes, small vesicles, large organelles like mitochondria are transported over microtubules by motor proteins from the cell-body into axons and dendrites to supply synapses with essential building blocks and energy for maintenance and renewal. A functionally stable but dynamically regulated microtubular architecture is thought to be essential for all brain activity, and it is essential to understand the molecular players and control mechanisms.

The importance of intraneuronal transport for normal functioning of the brain is dramatically illustrated by the devastating consequences when it goes wrong, e.g. in development leading to mental retardation, or in old age, causing dementia. Microtubule (MT)-mediated transport plays significant roles in many neurological disorders that are not understood in molecular detail. Normal physiological functions and related pathological defects are analysed since they are the most powerful approach to acquire fundamental knowledge of both sides of the problem.

The essential contribution of intracellular transport to proper neuronal functioning is dramatically illustrated by the great variety of neurodegenerative diseases, known as tauopathies, because they are characterised by fibrillar aggregates of hyper-phosphorylated protein tau. Protein tau is a naturally unfolded, Microtubule associated protein (MAPT) that promotes microtubule formation, stabilises their structure and their mutual spacing to allow cargos to pass along the neuronal processes.

The diversity in clinical symptoms, the severity and age of onset in tauopathies are thought to originate from deregulated transport in subsets of neurons in specified areas of the brain. Deregulation can be due to genetic, epigenetic and environmental factors that act alone or in combination. The spectrum of factors is thought to progressively impair the balance of kinase-phosphatase activities that dynamically control the phosphorylation state of tau. This in turn controls the binding of tau to microtubules, forming or stable, and thus the MT-mediated transport at different levels, in synapses, axons or dendrites and in different types of neurons. This hypothesis explains how clinically diverse neurodegenerative diseases could have a similar underlying mechanism related to phosphorylation of tau.

Amongst all the kinases, GSK3 was proposed as 'Tau-Kinase I', key to the phosphorylation of protein tau and thereby of its binding to microtubuli, helping to regulate traffic of the molecular motors that move over the microtubuli. Biochemical, genetic and cell-biological evidence implicated GSK3, directly or indirectly, in the pathological hyper-phosphorylation of protein tau in Alzheimer's disease (AD) and in Frontotemporal dementia (FTD). Protein tau that becomes abnormally phosphorylated on specified serine and threonine residues, accumulate in diseased neurons given rise to the typical 'tangled neurons' by silver impregnation that is essential for post-mortem pathological diagnosis.

Whether this is 'cause, consequence or correlation' remains to be defined experimentally. Basic mechanisms, physiological aspects, regional pathology, as well as progression with aging can only be studied in experimental model systems. Transgenic mice with amyloid pathology and tauopathy are generated and characterised, as in AD and FTD respectively. APPxTau bigenic mice with combined amyloid and tauopathy were studied in this project. In addition, GSK3a and cdk5 / p25 transgenic mice were implemented as fundamental pre-clinical models. Besides primary neuronal cultures, human neuroblastoma cells (SH-SY5Y) transfected with various isoforms and mutants of protein tau as in vitro models were used.

Studies were extended towards GSK3, by generating mice with neuron-specific deficiency in GSK3a or GSK3b, to define their respective fundamental contributions to the normal physiology and to the pathology of neurons in vivo. Their positive or negative contributions, i.e. synergism or rescue of amyloid and of tau pathology, was studied in vivo by cross-breeding in multiple transgenic mice.

The experimental genetics group engaged in fundamental studies of proteins involved in AD, i.e. APP, PS1, ApoE, protein tau and tau-kinases. The initial focus on the functions of APP and PS1 and of amyloid peptides was widened into fundamental studies of protein tau in neurons, in axonal and synaptic mechanisms in cognition and motor activity.

Project context and objectives:

WP1 - GSK3a and neuronal physiology
WP2 - GSK3 and pathology
WP3 - GSK3 up and down actors
WP4 - GSK3 inhibitors
WP5 - Management / dissemination / exploitation

Project results:

(i) promote integration and collaboration amongst partners;
(ii) monitor progression of tasks and WPs, adherence to the workplan;
(iii) disseminate results and inform interested parties and stakeholders by appropriate means, i.e. scientific publications, reports at meetings, lay-statements;
(iv) promote visibility to academic and industrial parties of research in the NEURO.GSK3 consortium;
(v) exploit scientific results, experimental models and compounds with commercial potential and social benefit by actively soliciting and promoting IP protection, pre-clinical validation, toxicology and further development in collaboration, in first instance with industrial partner #7, but in addition with other interested pharma and biotech companies.