Description
Mitochondria play a vital role in the visual system, with functions that include ATP production, to meet the high energy demand of phototransduction in photoreceptors and support the retinal pigment epithelium role in the visual cycle. Other roles include maintenance of the redox balance and calcium/stress homeostasis as well as the organisation of these organelles being proposed to direct light delivery in cone photoreceptors. Previous work from the group identified contacts between mitochondria and the plasma membrane, which are involved in the alignment of mitochondria between adjacent photoreceptors, suggesting a potential role of these contacts in intercellular communication.
This project aims to characterize the architecture of the mitochondria-plasma membrane contacts and determine their functional relevance in photoreceptor health, through both ultrastructural analysis and identification of their molecular regulators. We have used SH-SY5Y neuroblastoma cells as a tractable model, as they have mitochondria-plasma membrane contacts within the neurites.
To identify the proteins involved in these contacts, we have focused on setting up proximity-labelling to identify the tethering proteins at mitochondria-plasma membrane contact sites. These are based on an engineered ascorbate peroxidase (APEX2) and a pair of inactive fragments of a reconstitutable biotin ligase (TurboID), which enable biotinylation of proteins within a 10–20 nm radius of the contact sites. These biotinylated proteins can subsequently be isolated and assessed by mass spectrometry.
We have observed that treatment with FCCP leads to a marked reduction in mitochondria–plasma membrane contact sites. FCCP, a potent mitochondrial uncoupler, collapses the inner membrane proton gradient and induces rapid release of mitochondrial calcium into the cytosol. Therefore, these results raise the possibility that either membrane potential, mitochondrial calcium, or both regulate mitochondria–plasma membrane contacts. Preliminary experiments showed that pharmacological inhibition of the mitochondrial calcium uniporter reduced mitochondria–plasma membrane contacts, suggesting that mitochondrial calcium could be involved in the regulation of these contact sites.
Overall, identifying the proteins and mechanisms that regulate the formation of mitochondria–plasma membrane contacts, as well as their role in photoreceptors, may elucidate how dysfunction of these contacts contributes to disease pathogenesis and vision loss, and can provide molecular targets for future therapeutic interventions.
Lay Abstract
Mitochondria play a vital role in healthy vision, by producing energy, reducing cellular stress, and preserving chemical balance. Recent findings showed that mitochondria in these cells are in contact with the plasma membrane and align with those in neighbouring cells, suggesting that these contact sites may play a role in communication between cells and mitochondria.
This project aims to characterize the architecture of the mitochondria-plasma membrane contacts, as well as their role in photoreceptor health.
To identify the proteins involved in the mitochondria-plasma membrane contacts, we have focused on setting up methods to isolate proteins in between the mitochondria and plasma membrane. Once isolated, these proteins can be identified and the role they play in the mitochondria-plasma membrane contacts can be fully explored.
We have also discovered that calcium levels within the mitochondria appear to play a role in regulating their contacts with the plasma membrane.
By identifying the proteins and mechanisms that regulate the formation of mitochondria–plasma membrane contacts and their role in photoreceptors can help to understand how these mitochondria contact sites contributes to healthy vision and may provide targets for future therapeutic interventions.
| Lay Title | Unveiling the role of mitochondria-plasma membrane contacts in healthy vision |
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| Role | Postdoctoral Researcher |