Decoding subtype development and function in human pluripotent stem cell-derived midbrain dopaminergic neurons

Midbrain dopaminergic (mDA) neurons exist as molecularly and functionally distinct subtypes with varying sensitivity to neurodegenerative and psychiatric disorders. However, the factors that determine these subtype identities remain unclear, and methods for the targeted derivation of specific human mDA subtypes are limited. In this study, researchers developed a method to generate substantia nigra (A9) and ventral tegmental area (A10) mDA neurons from human pluripotent stem cells (hPSCs).

The A9 subtype identity is determined by a dual-SMAD activation mechanism involving Activin A and BMP7 at the midbrain floor-plate progenitor stage. Conversely, A10 identity is promoted by inhibiting BMP signaling. The A9 mDA neurons can be distinguished by their ALDH1A1 expression, and their identity is preserved through continued modulation of TGF-{beta} signaling and the activation of ESRRB both in vitro and after transplantation in living organisms.

Single-cell RNA sequencing and biochemical assessments revealed that hPSC-derived A9 neurons display heightened oxidative phosphorylation, neuromelanin-like pigmentation, increased dopamine synthesis and release, and electrophysiological properties comparable to in vivo A9 mDA neurons. When compared to human fetal midbrain datasets, the in vitro-derived mDA subtypes showed a high degree of transcriptional similarity.

The findings from this work demonstrate that hPSC-derived A9 neurons secrete neuromelanin-like structures that trigger pro-inflammatory cytokine production from hPSC-derived microglia. Moreover, A9 neurons have the capability to upregulate MHC-I genes in response to interferon-gamma, characteristics that contribute to the selective vulnerability of A9 neurons.

The development of this robust in vitro platform allows for further exploration of human mDA subtype development, function, and susceptibility to disease, ultimately paving the way for mechanistic studies relevant to Parkinson's disease and the potential creation of cell-based therapies.