Application of Small Molecules in the Central Nervous System Direct Neuronal Reprogramming

Abstract

The lack of regenerative capacity of neurons leads to poor prognoses for some neurological disorders. The use of small molecules to directly reprogram somatic cells into neurons provides a new therapeutic strategy for neurological diseases. In this review, the mechanisms of action of different small molecules, the approaches to screening small molecule cocktails, and the methods employed to detect their reprogramming efficiency are discussed, and the studies, focusing on neuronal reprogramming using small molecules in neurological disease models, are collected. Future research efforts are needed to investigate the in vivo mechanisms of small molecule-mediated neuronal reprogramming under pathophysiological states, optimize screening cocktails and dosing regimens, and identify safe and effective delivery routes to promote neural regeneration in different neurological diseases.

Generation of Functional Neurons From Adult Human Mucosal Olfactory Ensheathing Glia by Direct Lineage Conversion

“…To enhance and facilitate neuronal direct reprogramming, several authors have turned to the use of small molecules that target neurogenic signaling pathways (Bocchi et al, 2022; Vasan et al, 2021; Wang et al, 2022). For such purpose, we added different combinations of small molecules to the NEUROD1-transduced cells (summarized in Supplemental Table 2).…”

“…To enhance neuronal direct reprogramming, several authors made use of small molecules that target neurogenic signaling pathways (Ma et al, 2021; Ninomiya et al, 2023; Wang et al, 2022). This approach overcomes the concern of introducing foreign genetic material to cell cultures that might be potentially used for cell-based therapy.…”

“…We added different combinations of small molecules to the NEUROD1-transduced cells or to hmOEG without overexpression of any transcription factors, but no combination improved the reprogramming results obtained with the transcription factor NEUROD1. This scenario has already been addressed by some authors (Vasan et al, 2021; Wang et al, 2022) who note the challenge to seek an optimal formula to achieve acceptable conversion efficiency: not only the optimal concentration of each small molecule in the cocktails is difficult to determine but also the length of the induction time is a concern, as longer times can have toxic effects on the cells, while shorter times might not be effective in inducing neuronal conversion.…”

Small molecules fail to induce direct reprogramming of adult rat olfactory ensheathing glia to mature neurons

“…This constraint to achieve the direct conversion of somatic cells to neurons only with pharmacological tools has already been highlighted by Vasan et al (2021) and Wang et al (2022), who note the challenge to seek an optimal formula to achieve acceptable conversion efficiency: not only the optimal concentration of each small molecule in the cocktails is difficult to determine but also the length of the induction time is a concern, as longer times can have toxic effects on the cells, while shorter times might not be effective in inducing neuronal conversion.…”

“…Mechanistically, chemical reprogramming of astrocytes into neurons is mediated through both epigenetic and transcriptional regulation, activating proneural transcription factors such as NEUROD1, NGN2, and ASCL1 (Yin et al, 2019). Combinations of the following small molecules are commonly used in direct reprogramming strategies (Vasan et al, 2021;Bocchi et al, 2022;Wang et al, 2022): CHIR99021 (GSK3 inhibitor), SB431542 (TGFβ receptor inhibitor), DAPT (gamma-secretase inhibitor), forskolin (FSK) (PKA activator in cAMP signaling pathway), smoothened agonist (SAG) (Sonic hedgehog-SHH-activator), purmorphamine (SHH activator), valproic acid (HDAC inhibitor), IBET-151 (BET bromodomain inhibitor), isoxazole9 (ISX-9, inducer of adult neural stem cell differentiation), and/or LDN193189 (BMP pathway inhibitor).…”