DIRECT REPROGRAMMING OF GLIA INTO FOREBRAIN INTERNEURONS IN HUMAN TISSUE CULTURES

Inhibitory interneurons, particularly parvalbumin (PV) cells, are essential for maintaining cortical excitation-inhibition balance and their dysfunction is linked to neurological disorders such as epilepsy and schizophrenia. Interneuron transplantation, derived from e.g. stem cells, has shown symptom relief in animal models but to derive PV interneurons remains challenging and requires extended timeline. Direct reprogramming represents a promising alternative where a somatic cell, such as glial cell, can be converted into interneurons through the forced expression of neuronal genes. The process bypasses the tumorigenic stem cell state enabling in vivo application targeting resident glia.

Here, we applied direct interneuron reprogramming within adult human brain tissue using human glial progenitor cells (hGPCs). These cells show successful PV conversion in vitro with reduced glial markers and increased neuronal and GABAergic gene and protein expression, including TAU, GABA, and PV, within 21 days. hGPCs were transfected with interneuron reprogramming factors and transplanted into adult human cortical organotypic slice cultures, uniquely available in our environment. Reprogramming was induced using doxycycline administration. Results show that transplanted hGPCs survived, migrated into host tissue and acquired neuronal morphology after two weeks. A substantial fraction further expressed GABA and a subset expressed PV, demonstrating interneuron reprogramming in human tissue. After four weeks, GABA expression persisted indicating a stable inhibitory phenotype, although PV expression declined.

These findings shows first proof-of-concept of in situ glia reprogramming directly within human brain cortical tissue. This paradigm has potential for future in vivo cell repair strategies for neurological disorders where interneurons are lost or dysfunctional.