Bioenergetic regulation and neuronal differentiation NaBt mediated

da | Giu 4, 2018 | Biologia Molecolare

The nervous system is one of the most important and studied component of our body, in particular the interest has been recently focused on neuronal differentiation from neuroprogenitor cells. This process is regulated by the different states of heterochromatin that is characterized by specific epigenetic marks; notably a high acetylation level is associated to neuronal fate, while medium and low levels bring to astrocytic and oligodendrocytic fate respectively [1]. The differentiation mechanism requires lot of energy provided through oxidative phosphorylation into mitochondria and the amount of these important organelles is stimulated by mitochondrial transcription factor A (TFAM) [2]. Anne Chiaramello’s working group has studied Sodium Butyrate (NaBt, an inhibitor of histone deacetylases also known as HDACs) effects on neuroprogenitor model cells behaviour: PC12-NeuroD6 are neuronal crest derivates are a model system used to study   neuronal differentiation. These cells are modified to express constitutively neuroD6 gene, which induces neuronal fate [3] and tfam transcription [4]. Recently, the same team has carried out another study on neuroprogenitor cells [5]. They treated PC12-ND6 cells with NaBt to inhibit histone-deacetylases activity and found an increase acetylation on the lysine residues of the histone H3. At cellular level, they observed a higher amount and ultrastructural changes of mitochondria in NaBt-treated cells. NaBt promotes the transcription of the Nuclear Respiratory Factor 1 (NRF1), which regulates positively TFAM expression and mitochondrial biogenesis. Since mitochondria are involved in bioenergetic metabolism, the authors also measured two typical metabolic parameters: Oxygen Consumption Rate (OCR) and Extra Cellular Acidification Rate (ECAR). NaBt-treated cells showed a gain of these indicators. Moreover they observed an increase of mitochondrial membrane potential through MitoTracker Red, a red fluorescent dye that stains mitochondria according to their membrane potential.

An important phase of neurogenesis is neurite growth that requires a large quantity of energy. The authors induced this process through Nerve Growth Factor (NGF) treatment and evaluated NaBt effects. Results showed that the presence of many mitochondria, induced by NaBt treatment, promotes neurite outgrowing: this phenomenon was observed in cells subjected to a prolonged pre-treatment with NaBt that allows the acquisition of a useful mitochondrial number. So, the researchers also associated this behaviour with the timing of administration.

The CREB-Binding Protein (CBP), is a regulator of epigenetic state of chromatin through its acetyltransferase activity and in this study it was discovered that its expression is stimulated in NaBt-treated cells. It was also demonstrated that CBP is important to regulate number, morphology, and efficiency of mitochondria: in cbp-knockdown cells mitochondrial mass was lower and it was observable a swollen morphology associated to a defective activity of these organelles.

The last step was a bioinformatics study to analyse the pattern of the epigenetic mark H3K27ac on cells treated with NaBt for 3 days. The ChIP-seq analysis revealed a distribution of acetylated sites in different genomic regions: 13% introns, 18% exons, 25% promoters and 43% in intergenic regions. Subsequently, they performed a gene ontology analysis by PANTHER that revealed in particular an enrichment on cellular metabolic and neurotrophic genes. Further studies, based on STRING database, showed an enrichment on more neuronal genes and genes encoding mitochondrial ribosomal proteins (MRPs) involved on oxidative phosphorylation mechanism. Finally, researchers validated that NaBt promotes H3K27ac epigenetic mark, realizing a ChIP-qPCR analysis on 5 genes containing this modification.

In conclusion, this study has revealed an important correlation between epigenetic modifications, induced by NaBt, and activation of differentiation that involves both metabolic and bioenergetic processes in neuroprogenitor cells. This work represents an interesting starting point to elucidate the relationship between gene expression and metabolic processes on neuronal differentiation: it is an innovating and easy idea to act on metabolic, neurodegenerative and mitochondrial dysfunctions because it is based on the administration of a simple molecule like NaBt. However, remains a lot of work to do because there are plenty of unclear points. The results reported on this work are not sufficiently detailed and there are misunderstandings on image captions, so is difficult to draw exact conclusions.

In this picture are summarized the processes induced by sodium butyrate, which in turn stimulate neuroprogenitor cells differentiation in neurons. In red the pathway that stimulates mitochondrial biogenesis is represented, while in green the one that controls DNA epigenetic regulation, in particular the acetylation on the histone H3 lysine residues (H3K27ac). Furthermore, the ability of NaBt to inhibit histone-deacetylases (HDAC) is shown in pink and this leads to an increase in DNA acetylation level

References

  1. Shen, J. Li and P. Casaccia-Bonnefil. Histone modifications affect timing of oligodentrocyte progenitor differentiation in the developing rat brain. J. Cell Biol. 169, 577-589 (2005).
  2. Larsson, J. Wang, H. Wilhelmsson, A. Oldfors, P. Rustin, M. Lewandoski, G. S. Barsh and D. A. Clayton. Mitochondrial transcription factor A is necessary for mtDNA maintenance and embryogenesis in mice. Nature genetics. 18, 231-236 (1998).
  3. K. Baxter, M. Uittenbogaard, J. Yoon and A. Chiaramello. The neurogenic basic helix-loop-helix transcription factor NeuroD6 concomitantly increases mitochondrial mass and regulates cytoskeletal organization in the early stages of neuronal differentiation. ASN Neuro. 1, 195-211 (2009).
  4. K. Baxter, M. Uittenbogaard and A. Chiaramello. The neurogenic basic helix-loop-helix transcription factor NeuroD6 enhanced mitochondrial biogenesis and bioenergetics to confer tolerance of neuronal PC12-NeuroD6 cells to the mitochondrial stressor rotenone. Exp Cell Res. 318(17), 2200-2214 (2012).
  5. M. Uittenbogaard, C. A. Bratner and A. Chiaramello. Epigenetic modifiers promote mitochondrial biogenesis and oxidative metabolism leading to enhanced differentiation of neuroprogenitor cells. Cell death and disease. 9, 360 (2018).

Piera Iovino

Master Industrial Biotechnology student

Marta Vassallo

Master Industrial Biotechnology student

 

Apri un sito e guadagna con Altervista - Disclaimer - Segnala abuso - Privacy Policy - Personalizza tracciamento pubblicitario