Human assembloid model of the ascending neural sensory pathway

Area of Science:

• Neuroscience
• Stem Cell Biology
• Genetics

Background:

• Somatosensory pathways transmit vital sensory information, including pain, touch, and proprioception, to the central nervous system.
• Understanding these pathways is crucial for developing effective pain therapeutics, but clinical translation is hindered by species-specific differences and a lack of suitable in vitro models.
• The polysynaptic nature of these pathways presents a significant challenge for in vitro modeling.

Purpose of the Study:

• To establish a human in vitro model of the spinothalamic somatosensory pathway.
• To investigate the functional assembly and activity of human sensory circuits.
• To explore the role of ion channels in pain perception using this novel model.

Main Methods:

• Generation of a four-part human ascending somatosensory assembloid (hASA) from human pluripotent stem cells, integrating somatosensory, spinal, thalamic, and cortical organoids.
• Transcriptomic profiling to identify key cell types within the assembled circuit.
• Rabies tracing and calcium imaging to map neuronal connectivity and activity.
• Extracellular recordings to assess synchronized network activity.
• Functional assessment by manipulating the sodium channel Na_V1.7 (encoded by SCN9A).

Main Results:

• The hASA model successfully integrated distinct organoids, forming a functional spinothalamic pathway with key cell types identified via transcriptomics.
• Neuronal tracing and calcium imaging confirmed functional connections from sensory neurons to spinal and thalamic neurons.
• Noxious chemical stimulation elicited coordinated responses within the hASA, with synchronized activity observed across the assembloid.
• Disruption of Na_V1.7 function (loss-of-function) impaired network synchrony, while a gain-of-function variant induced hypersynchrony, demonstrating the model's sensitivity to ion channel function.

Conclusions:

• The human ascending somatosensory assembloid (hASA) provides a functional in vitro model of the human spinothalamic pathway.
• This model enables the study of sensory circuit assembly, function, and the impact of genetic variations on pain perception.
• hASA holds significant potential for accelerating the understanding of sensory pathways and facilitating the development of novel pain therapeutics.