Functional maturity of motor neurons derived from control and ALS patient iPSCs is affected by human iPSC-derived astrocytes
Creators: name: Chouhan, Amit K.
name: Bhuvaneish T. Selvaraj
name: Gane, Angus
name: Arpan R. Mehta
name: Burr, Karen
name: Shaw, Christopher E.
name: Siddharthan Chandran
name: Miles, Gareth B.
Publisher: name: F1000 Research Limited
Year: 2017

description: Background:<br>Changes in the input-output relationship, or excitability, of human motor neurons (MNs) occur during normal maturation [1]. Given the recent demonstration that MN excitability is altered in human induced pluripotent stem cell (iPSC)-based models of ALS [2], it is crucial that models utilised to study such pathophysiology exhibit signs of functional maturity.  Studies involving the co-culture of rodent astrocytes with human or rodent neurons have shown that astrocytes contribute to changes in the firing properties of neurons [3].<br> <br>Objectives:<br>This study aimed to investigate the interaction between astrocytes and MNs derived from human iPSCs and the potential influences of astrocytes on the functional maturity and excitability of MNs.<br> <br>Methods:<br>Two different protocols were utilised for iPSC differentiation; one producing MN-enriched cultures and the other producing astrocyte-enriched cultures. MNs were either cultured alone or on top of a monolayer of astrocytes. MNs and astrocytes were derived from iPSCs from either control individuals or ALS patients harbouring C9orf72 mutations. The function of MNs was investigated using whole-cell patch-clamp recordings.<br> <br>Results:<br>When comparing cultures of MNs grown alone versus co-cultures of MNs with astrocytes we found that control astrocytes influence the functional maturation of both control and ALS patient iPSC-derived MNs. This was evidenced by changes in the intrinsic properties of MNs including increased whole-cell capacitance, decreased input resistance and more hyperpolarised resting membrane potentials when co-cultured with astrocytes. Astrocytes also influenced the functional output of MNs, with their presence leading to increased levels of synaptic activity, greater excitability and higher frequencies of action potential firing. No clear differences in total voltage-activated sodium or potassium currents were observed, suggesting subtle effects on specific channel subtypes underlie changes in functional MN output associated with the presence of astrocytes.<br> <br>Discussion and conclusions:<br>Our data reveals involvement of human astrocytes in the functional development of human MNs. The presence of control astrocytes is sufficient to impact the functional maturity of both control and ALS patient iPSC-derived MNs. These findings highlight the importance of considering astrocyte-neuron signalling when utilising cell culture-based models of ALS and provide further support for the utility of non-cell autonomous mechanisms as potential targets for novel ALS therapeutics.<br> <br>References:<br> <br>[1] Tadros MA, Lim R, Hughes DI, et al. Electrical maturation of spinal neurons in the human fetus: comparison of ventral and dorsal horn. J Neurophysiol. 2015; 114:2661-71.<br> <br>[2] Devlin AC, Burr K, Borooah S, et al. Human iPSC-derived motoneurons harbouring TARDBP or C9ORF72 ALS mutations are dysfunctional despite maintaining viability. Nat. Commun. 2015;6:5999.<br> <br>[3] Johnson MA, Weick JP, Pearce RA, et al. Functional neural development from human embryonic stem cells: accelerated synaptic activity via astrocyte coculture. J Neurosci. 2007;27:3069-77.<br> <br>Acknowledgement: Supported by the MNDA and The Euan MacDonald Centre.