The continuing demographic shift to an older population has highly increased the prevalence of chronic neurodegenerative diseases that represent a significant burden to our health care system and families. Parkinson’s disease (PD) is the second most common neurodegenerative disease after Alzheimer’s disease, affecting about 1- 3% of the population over the age of 55. PD affects 1.1 million persons in the EU and 6.3 million worldwide. Current drug therapies for PD are exclusively symptomatic and are incapable of delaying or arresting the disease progression. Thus, despite the major efforts int eh field disease-modifying therapies have not yet available. A reason for this are the current limitations in modeling neuronal diseases in a laboratory setting in order to progress fast from discovery to therapeutics. In PD the Dopaminergic (DAergic) neurons of the substantia nigra pars compacts are progressively degenerating causing the loss of the nigrostriatal pathway and the development of the motor disturbances. Why these neurons are the most vulnerable in this disease in not fully understood. Patient-specific stem cells (iPSCs) can be generated and differentiated in DAergic neurons however conventional neuronal cultures fail to recapitulate the nigrostriatal pathway preventing to study the vulnerability of this circuitry in PD.
In this project we adapted a microfluidic platform to organize a patterned circuitry between human iPSC-derived DAergic and striatal medium spiny neurons (MSNs) for in vitro modeling of the nigrostriatal circuitry. This platform provided us with the opportunity to study pathologically relevant processes in long-term cultures of iPSC neuronal derivatives with spatially orchestrated functional connectivity mirroring the brain nigrostriatal pathway affected in PD.
We defined the conditions to plate, differentiate and maintain human neurons in long-term cultures within a microfluidic environment. In addition, we established a procedure to culture two independent neuronal populations on the same chip and promote the formation of lasting and functional connections. iPSC-derived DAergic and MSNs in long-term cultures on-the-chip maintained healthy and stereotyped morphology and expressed multiple key markers of their neuronal subtype identity.
We showed that iPSC-derived DAergic and MSNs can form stable synapses with active pre-synaptic terminals that can activate post-synaptic dopaminergic receptors on MSNs. The establishment of this neuronal circuit uncovers multiple opportunities for basic biology and disease-relevant studies. In particular, the spatial and fluidic isolation of the synaptic compartment obtained with this system offers an advantageous setting to evaluate the effects of toxins, inflammatory signals and other chemicals on human synaptic function. Additionally, the detrimental effects of aggregated alpha-synuclein and amyloid toxic species on synaptic activity described in murine models can be further addressed in this human culture system.
