# Metformin Restores Mitochondrial Function and Neurogenesis in POLG Patient‐Derived Brain Organoids

## TL;DR

Metformin helps fix mitochondrial issues and boosts neuron growth in brain organoids from patients with POLG mutations, suggesting it could treat related neurodegenerative diseases.

## Contribution

The study demonstrates metformin's ability to restore mitochondrial and neural function in POLG-related disorders using patient-derived organoids.

## Key findings

- Metformin treatment restores neuronal identity and subtype-specific gene expression in POLG mutant organoids.
- Metformin improves mitochondrial function, increases mtDNA copy number, and reduces oxidative stress.
- Metformin induces metabolic reprogramming involving TCA cycle and redox pathways.

## Abstract

Mitochondrial dysfunction and impaired neurogenesis are central to mitochondrial DNA polymerase (POLG)‐related disorders, yet therapeutic options remain limited. Here, patient‐derived induced pluripotent stem cell (iPSC)‐based cortical organoids are used to model POLG‐associated neurodegeneration and assess the therapeutic potential of metformin. Single‐cell RNA‐seq reveals distinct vulnerabilities in dopaminergic, glutamatergic, and GABAergic neuronal subtypes, with dopaminergic neurons exhibiting the most severe loss and mitochondrial transcriptomic deficits. Metformin treatment (250 µm, 2 months) significantly restores neuronal identity, subtype‐specific gene expression, and mitochondrial function. Functional assays demonstrate improved mitochondrial membrane potential (TMRE), increased mitochondrial mass (MTG, MTDR), and reduced oxidative stress (MitoSOX, BAX/cleaved caspase 3). Notably, mitochondrial DNA (mtDNA) copy number and the expression of mitochondrial replisome proteins (POLG, POLG2) are upregulated, indicating enhanced mitochondrial genome maintenance. Calcium measurement confirms improved neuronal excitability. Untargeted metabolomics further reveals metformin‐induced metabolic reprogramming, including enrichment of the tricarboxylic acid (TCA) cycle, amino acid metabolism, and redox‐related pathways. Together, these findings demonstrate that metformin enhances mitochondrial integrity and neural function across multiple neuronal subtypes and offer mechanistic insights into its potential as a treatment for POLG‐related disorders.

Patient‐derived POLG‐mutant cortical organoids reveal neuronal subtype‐specific mitochondrial and synaptic defects, with dopaminergic neurons most affected. Metformin treatment restores neuronal identity, mitochondrial function, and excitability, increased mtDNA maintenance, and reprogrammed metabolism via TCA and redox pathways. These results highlight metformin's potential to treat POLG‐related neurodegeneration through mitochondrial repair and functional restoration.