Molecular Mechanisms of Neurodegeneration and the Development of Neuroprotective Strategies

Professor Jacqueline de Belleroche

Familial Motor Neurone Disease/ Amyotrophic Lateral Sclerosis: identification of new FALS loci and the elucidation of mechanisms of pathogenesis using gene expression, cell culture and experimental models.

A prominent feature of a number of neurodegenerative conditions such as Parkinson’s disease (PD), amyotrophic lateral sclerosis/ motor neuron disease (ALS) and frontotemporal dementia (FTD) is the build-up of misfolded proteins leading to the formation of ubiquitinated protein aggregates (Bandopadhyay and de Belleroche 2010). The Neurogenetics Group at Imperial College London has focussed on the identification of pathogenic mutations causing the familial form of ALS including ALS with FTD and has recruited over 200 families to this study. ALS is a late-onset, severe, debilitating condition affecting spinal cord, brain stem and cortical motor neurones causing progressive muscle weakness, atrophy, paralysis and leading finally to respiratory failure. There have been considerable advances in the understanding of disease progression from studies on the dominantly inherited familial form of ALS (FALS) which, although rare, accounting for 5% of cases, is clinically indistinguishable from the sporadic form of the disease.To date, mutations have been identified in ~70% of these families which either directly affect the removal of misfolded proteins through the unfolded protein response (UPR) (e.g. VAPB), endoplasmic reticulum associated protein degradation (ERAD) (e.g. valosin-containing protein (VCP), ubiquitin-proteasome system (UPS), removal of ubiquitinated aggregates through autophagy (e.g. VCP) or are associated with ubiquitinated inclusions (e.g. Fused in sarcoma and TAR DNA binding protein) (Sreedharan et al., 2008: Vance et al., 2009: Chen et al., 2010; Michell et al., 2009). TDP-43-positive ubiquitinated protein inclusions are a hallmark of most forms of ALS, including sporadic ALS and contribute to other neurodegenerative conditions such as FTD.

The most recently identified mutations causing ALS, FTD or ALS/FTD are large hexanucleotide repeat expansions found in a gene of unknown function, C9ORF72 (Renton et al., 2011; DeJesus-Hernandez et al., 2011), which  account for 38% of familial cases of ALS and 6% of sporadic cases in the UK and is characterised by TDP-43-positive ubiquitinated inclusions. The elucidation of pathogenic mechanisms of disease caused by multiple pathways is of great significance to the understanding of a wide range of neurodegenerative conditions and is now greatly empowered by the identification of causal mutations and is a major objective of our research group using a range of analytical tools (Figure 1).

Figure 1: Gene expression in spinal cord, sequence analysis and the use of cell culture to model pathogenic mechanisms occurring in motor neurones

The neuroprotective properties of heat shock proteins (HSPs).

HSPs function as molecular chaperones and facilitate protein folding. Whilst some are constitutively expressed, others are specifically induced in response to cell stress, e.g. HSP27, HSP70, and serve to chaperone denatured /aberrant proteins for refolding /degradation and furthermore reduce protein aggregation. In addition, these HSPs suppress apoptosis by interaction with cyt c in caspase-dependent apoptosis and Daxx in Fas mediated cell death. We have characterised the properties of inducible HSPs with particular relevance to their role in neurological disorders such as ALS, stroke, epilepsy, Parkinson’s disease and nerve injury and have been able to demonstrate significant neuroprotective effects of HSP27 in vivo (e.g. van der Weerd  et al., 2010: Sharp et al., 2006: Sharp et al., 2008)  Collaborative projects extend to other models, including diabetes and atheroprotection (Rayner et al.,2009: Dai et al.,2009).

Figure 2: HSP27 expression in spinal cord tissue sections

Gene Expression in Schizophrenia

Schizophrenia is characterised by a constellation of symptoms which include hallucinations, delusions, disorganised thought, impaired motivation and cognitive impairment (Reed and de Belleroche 2011).  The underlying causes are little understood, only subtle structural changes are seen and several genes are thought to contribute to susceptibility. Our overall aim is to obtain insight into the underlying molecular changes occurring in schizophrenia through the analysis of gene expression in cerebral cortex of schizophrenia patients compared to normal controls using a range of complimentary experimental approaches. Most recently, we carried out an extensive expression analysis, which demonstrated that major changes occur in schizophrenia in synaptic proteins associated with synaptic plasticity (Maycox et al., 2010: Barnes et al., 2011)( Figure 3). Furthermore, our analysis showed that changes in the expression of 50 genes were also found in a US cohort (Harvard Brain Bank) carried out in an independent study.

Figure 3: Gene expression profiling in schizophrenia