Impressions du congrès de la SETGyC de Mallorca - Aurélie Mouka

Disease modelling using iPSCs :
Novel insights into Parkinson’s disease through iPSC-based technology Angel Raya, CMRB, Barcelona

Aurélie Mouka, Hôpital Antoine-Béclère
un de nos boursiers est revenu du congrès de Mallorca avec les impressions suivantes...

Recently, the generation of patient-specific cellular models of diseases has been possible by means of the emerging technology of human induced pluripotent stem cells (hiPSCs). The hiPSCs represent a new system offering unique advantages for therapy and in vitro disease modeling helping understanding the molecular basis of developmental processes.

During this congress, several example of the use of iPS cells for disease modelling have been been discussed. One of them, concerning Parkinson’s disease (PD) modelling, presented by Dr Angel Raya, represents a perfect example of the importance and potential for iPS cell technology in the future for modeling neurodegenerative diseases.

PD is the second most common neurodegenerative disease which is mainly characterized by dopaminergic neuron degeneration and synaptic dysfunction. The generation of disease-specific iPSC from patients suffering from PD has already highlighted others phenotypes such as abnormal accumulation of α-synuclein. About 85-90% of PD cases are sporadic and the genetic basis of these cases remains poorly understood. LRRK2 (Leucine-rich repeat kinase 2) G2019S mutation is the most common genetic cause of both familial and sporadic PD identified to date. But so far, the impact of this mutation remains unclear. Indeed, patients carrying LRRK2 G2019S mutation are very likely to developed Parkinson disease (80% penetrance) during their lifetimes. But some of them develop the disease at 50, others at 80 years old and some never develop Parkinson's symptoms. So there are probably factors that protect these patients to develop the disease. Researchers believe onset is due to a combination of genetic and environmental factors.

In his talk, Dr Angel Raya has dissected the specific contribution of the LRRK2 G2019S mutation and the background to the onset of the disease. For that purpose, iPSCs lines were generated from PD patients as well as asymptomatic LRRK2 carriers and from healthy control. Then, following neuronal differentiation, three characteristics were evaluated: α-synuclein accumulation, morphological defects and cell death.

As expected, neurons-derived iPSC from healthy control did not show any of this three characteristics. After gene-editing strategy for mutation correction (TALENS), they were able to show that when this mutation was removed from iPSC-derived neurons from PD patients, no more accumulation of α-synuclein were observed. Neurons aged normally and did not degenerate. In contrast, following LRRK2 G2019S mutation insertion (Crispr/cas9) in iPSC-derived neurons from healthy patients, neurons developed Parkinson's symptoms. In this way, understanding the role of LRRK2 in iPSCs represents a good model for studying the progression of PD. But do this specific mutation is fully penetrant?

Author also generated iPSC from very old patients that carried this particular mutation but did not have developed the disease. Interestingly, in asymptomatic carrier iPSC-derived neurons, two discordant phenotypes were observed. Asymptomatic carrier iPSC-derived neurons recapitulates LRRK2-specific PD phenotype such as α-synuclein accumulation and neurite pathology but showed less susceptibility to neurodegeneration compared to those derived from patients carrying LRRK2 mutation that did developed the disease. Something happened in this patients that prevent them to develop neuronal degeneration and so the disease.

The genome of patients included in this study was then sequenced in an attempt to identified potential rare variants that could explained the protection against PD. The poster presented by C. Calatayud, showed that two variants were identified, one showing a trend toward a delayed onset (GAK) and another one that seems to be significantly associated (SCARB2).

Another aspect of this study showed also that when normal neurons were cultured with iPSC-derived astrocytes from PD patients, these neurons degenerated. PD patient’s astrocytes seem to impede neuronal survival. Furthermore, α-synuclein protein aggregates accumulate in astrocytes whereas normal astrocytes don’t normally express this specific protein. Their results suggest that astrocytes dysfunction may play a role in PD.

In conclusion, this study shows that iPSC-based models can recapitulate PD disease phenotype as well as the late-onset phenotypes. iPSC-based models is beginning to provide important insights into pathogenic mechanism and genetic basis of PD. Identification of genetic factors that cause Parkinson will certainly lead to the development of better diagnosis, improved disease models, and in time, to the development of better treatment.