Cell Fate and Metabolism
We investigate the mechanisms driving the direct reprogramming of differentiated mouse and human cells into functional neurons, aiming at a comprehensive understanding of the conversion process with the final aim of further improvement of purity and quality of the induced neurons.
Leveraging state-of-the-art technologies — including single-cell multiomics, proteomics, metabolomics and high-content imaging — we aim to understand the extent to which the identity of differentiated cells can be manipulated to generate new neurons that are functionally and molecularly similar to those present in the adult healthy brain.
We investigate the mechanisms driving the direct reprogramming of differentiated mouse and human cells into functional neurons, aiming at a comprehensive understanding of the conversion process with the final aim of further improvement of purity and quality of the induced neurons.
Leveraging state-of-the-art technologies — including single-cell multiomics, proteomics, metabolomics and high-content imaging — we aim to understand the extent to which the identity of differentiated cells can be manipulated to generate new neurons that are functionally and molecularly similar to those present in the adult healthy brain.
About our Research
We have shown that mitochondrial activity plays a crucial role in the direct neuronal reprogramming of both mouse (Gascon et al., 2016; Russo et al., 2020) and human astrocytes (Sonsalla, Malpartida et al., 2024). Beyond their role in ATP production, mitochondria contribute to redox homeostasis by regenerating NADH to NAD+. Notably, treatment with nicotinamide riboside (NR), a precursor of NAD+, enhances the generation of induced neurons (iNeurons) from human astrocytes while reducing aggregate formation in iNs.
Here, we investigate whether NR-mediated improvements in neuronal conversion are solely due to its redox function or also involve NAD+-dependent enzymes, such as nuclear sirtuins.
A surprising findings of our previous work is that the mitochondrial proteome differs between astrocytes and neurons, and successfully induced neurons downregulate astrocyte-enriched mitochondrial proteins and upregulate neuron-enriched mitochondrial proteins (Russo et al., 2020). More recently, we identified the unfolded protein response (UPR) as a major hurdle in the direct neuronal reprogramming of human astrocytes (Sonsalla, Malpartida et al., 2024). Given that UPR primarily occurs in the endoplasmic reticulum (ER), it is plausible that the ER proteome also differs between astrocytes and neurons.
To build on these findings, we seek to determine the extent to which organelles vary across cell types and how their proteome—and consequently their function—must change during astrocyte-to-neuron reprogramming. Here, we aim to characterize the proteome of various organelles and track their dynamics during neuronal conversion to assess whether these changes act as additional roadblocks in the process.
Ascl1 and Neurogenin2 are proneural transcription factors with pioneering activity, enabling them to access closed chromatin and initiate a transcriptional program that drives neuronal identity. However, how different cellular contexts influence this conversion process remains poorly understood (Kempf, Knelles, Hersbach et al., 2021).
Here, we aim to compare the mechanisms triggered by the same reprogramming factor in different starting cell types (e.g., astroglial cells isolated from distinct CNS regions) and to identify both universal and cell-specific principles that govern direct neuronal reprogramming.
In vitro model systems are valuable for studying the molecular mechanisms underlying processes like direct reprogramming. However, they often lack the complexity of in vivo environments, such as the brain, particularly its three-dimensional architecture.
Here, we aim to establish a novel model system that integrates the advantages of in vitro models—such as ease of handling, scalability, and compatibility with imaging and analysis—with key aspects of a 3D environment, including spatial organization and cellular diversity. This system will allow us to assess how these factors influence direct neuronal reprogramming.
Over the years, we have identified genetic (e.g., REST), metabolic (e.g., ROS), and post-translational (e.g., UPR) barriers that hinder direct neuronal reprogramming. Beyond conceptual understanding of the conversion process, we are also performing screens with repruposing drugs to enhance the conversion process using high-content screening approaches and to investigate the molecular mechanisms underlying their effects.
We have shown that mitochondrial activity plays a crucial role in the direct neuronal reprogramming of both mouse (Gascon et al., 2016; Russo et al., 2020) and human astrocytes (Sonsalla, Malpartida et al., 2024). Beyond their role in ATP production, mitochondria contribute to redox homeostasis by regenerating NADH to NAD+. Notably, treatment with nicotinamide riboside (NR), a precursor of NAD+, enhances the generation of induced neurons (iNeurons) from human astrocytes while reducing aggregate formation in iNs.
Here, we investigate whether NR-mediated improvements in neuronal conversion are solely due to its redox function or also involve NAD+-dependent enzymes, such as nuclear sirtuins.
A surprising findings of our previous work is that the mitochondrial proteome differs between astrocytes and neurons, and successfully induced neurons downregulate astrocyte-enriched mitochondrial proteins and upregulate neuron-enriched mitochondrial proteins (Russo et al., 2020). More recently, we identified the unfolded protein response (UPR) as a major hurdle in the direct neuronal reprogramming of human astrocytes (Sonsalla, Malpartida et al., 2024). Given that UPR primarily occurs in the endoplasmic reticulum (ER), it is plausible that the ER proteome also differs between astrocytes and neurons.
To build on these findings, we seek to determine the extent to which organelles vary across cell types and how their proteome—and consequently their function—must change during astrocyte-to-neuron reprogramming. Here, we aim to characterize the proteome of various organelles and track their dynamics during neuronal conversion to assess whether these changes act as additional roadblocks in the process.
Ascl1 and Neurogenin2 are proneural transcription factors with pioneering activity, enabling them to access closed chromatin and initiate a transcriptional program that drives neuronal identity. However, how different cellular contexts influence this conversion process remains poorly understood (Kempf, Knelles, Hersbach et al., 2021).
Here, we aim to compare the mechanisms triggered by the same reprogramming factor in different starting cell types (e.g., astroglial cells isolated from distinct CNS regions) and to identify both universal and cell-specific principles that govern direct neuronal reprogramming.
In vitro model systems are valuable for studying the molecular mechanisms underlying processes like direct reprogramming. However, they often lack the complexity of in vivo environments, such as the brain, particularly its three-dimensional architecture.
Here, we aim to establish a novel model system that integrates the advantages of in vitro models—such as ease of handling, scalability, and compatibility with imaging and analysis—with key aspects of a 3D environment, including spatial organization and cellular diversity. This system will allow us to assess how these factors influence direct neuronal reprogramming.
Over the years, we have identified genetic (e.g., REST), metabolic (e.g., ROS), and post-translational (e.g., UPR) barriers that hinder direct neuronal reprogramming. Beyond conceptual understanding of the conversion process, we are also performing screens with repruposing drugs to enhance the conversion process using high-content screening approaches and to investigate the molecular mechanisms underlying their effects.
Team Members
