Quality Control and Maintenance of Synaptic Mitochondria

Funder

Organizational Unit

Publications

Orchestrating mitochondria in neurons: Cytoskeleton as the conductor

Publication . Cardanho-Ramos, Carlos; Faria-Pereira, Andreia; Morais, Vanessa A.

Mitochondria are crucial to support synaptic activity, particularly through ATP production and Ca2+ homeostasis. This implies that mitochondria need to be well distributed throughout the different neuronal sub-compartments. To achieve this, a tight and precise regulation of several neuronal cytoskeleton players is necessary to transport and dock mitochondria. As post-mitotic cells, neurons are highly dependent on mitochondrial quality control mechanisms and several cytoskeleton proteins have been implicated in mitophagy. Therefore, all of these processes are orchestrated by the crosstalk between mitochondria and the neuronal cytoskeleton to form a coordinated and tuned symphony.

2020Journal article

Open access

Mitochondrial biogenesis in neurons: how and where

Publication . Cardanho-Ramos, Carlos; Morais, Vanessa A.

Neurons rely mostly on mitochondria for the production of ATP and Ca2+ homeostasis. As sub-compartmentalized cells, they have different pools of mitochondria in each compartment that are maintained by a constant mitochondrial turnover. It is assumed that most mitochondria are generated in the cell body and then travel to the synapse to exert their functions. Once damaged, mitochondria have to travel back to the cell body for degradation. However, in long cells, like motor neurons, this constant travel back and forth is not an energetically favourable process, thus mitochondrial biogenesis must also occur at the periphery. Ca2+ and ATP levels are the main triggers for mitochondrial biogenesis in the cell body, in a mechanism dependent on the Peroxisome-proliferator-activated γ co-activator-1α-nuclear respiration factors 1 and 2-mitochondrial transcription factor A (PGC-1α-NRF-1/2-TFAM) pathway. However, even though of extreme importance, very little is known about the mechanisms promoting mitochondrial biogenesis away from the cell body. In this review, we bring forward the evoked mechanisms that are at play for mitochondrial biogenesis in the cell body and periphery. Moreover, we postulate that mitochondrial biogenesis may vary locally within the same neuron, and we build upon the hypotheses that, in the periphery, local protein synthesis is responsible for giving all the machinery required for mitochondria to replicate themselves.

2021Journal article

Open access

Intestinal tissue-resident T cell activation depends on metabolite availability

Publication . Konjar, Spela; Ferreira, Cristina; Carvalho, Filipa; Figueiredo-Campos, Patricia; Fanczal, Júlia; Ribeiro, Sofia; Morais, Vanessa A.; Veldhoen, Marc

The metabolic capacity of many cells is tightly regulated and can adapt to changes in metabolic resources according to environmental changes. Tissue-resident memory (TRM) CD8+ T cells are one of the most abundant T cell populations and offer rapid protection against invading pathogens, especially at the epithelia. TRM cells metabolically adapt to their tissue niche, such as the intestinal epithelial barrier. In the small intestine, the types of TRM cells are intraepithelial lymphocytes (IELs), which contain high levels of cytotoxic molecules and express activation markers, suggesting a heightened state of activation. We hypothesize that the tissue environment may determine IEL activity. We show that IEL activation, in line with its semiactive status, is metabolically faster than circulating CD8+ T cells. IEL glycolysis and oxidative phosphorylation (OXPHOS) are interdependently regulated and are dependent on rapid access to metabolites from the environment. IELs are restrained by local availability of metabolites, but, especially, glucose levels determine their activity. Importantly, this enables functional control of intestinal TRM cells by metabolic means within the fragile environment of the intestinal epithelial barrier.

2022Journal article

Open access

Mitochondrial quality control pathways: PINK1 acts as a gatekeeper

Publication . Leites, Elvira; Morais, Vanessa A.

Mitochondria have a pivotal role in the maintenance of cell homeostasis and survival. Mitochondria are involved in processes such as ATP production, reactive oxygen species production, apoptosis induction, calcium homeostasis and protein degradation. Thus, mechanisms that regulate the intrinsic quality of mitochondria have a crucial role in dictating overall cell fate. The importance of these well-regulated mechanisms is highlighted in disease scenarios such as neurodegeneration, cancer and neuromuscular atrophy. How mitochondria senses and regulates their intrinsic quality control, and consequently cell survival, is still not fully understood. In this review, we discuss the pathways that are at present considered as state-of-the-art for mitochondria quality control regulation, and highlight a mitochondrial protein-PINK1-that has revealed to act as a mitochondrial gatekeeper able to sense the presence of healthy or damaged mitochondria.

2018Journal article

Restricted access

Unravelling mitochondrial dynamics and turnover in the synapse

Publication . Cardanho-Ramos, Carlos; Epifânio, Vanessa Alexandra dos Santos Morais

Neurons rely on mitochondria for ATP production and Ca2+ homeostasis, particularly at the synapse. As subcompartmentalized cells, they have different pools of mitochondria in each compartment. Achieving a non-uniform distribution requires mitochondria not only to be transported, but also to be retained in regions with high energy demands and high levels of Ca2+ . One of the goals of this thesis was to understand what makes mitochondria travel back and forward in a neuron and which mechanisms were activated to retain this organelle at the synapse. To address this, mouse primary neuron cultures, with fluorescent labelled mitochondria, were used to study the impact of the actomyosin cytoskeleton in mitochondrial transport and anchoring at the synapse. Taking advantage of a proteomic screen comparing synaptic with non-synaptic mitochondria, we selected two candidate proteins related with organelle movement: cell division control protein 42 (cdc-42), involved in actin polymerization; and myosin-VI, capable of anchoring mitochondria to actin cables. In the course of this project, a paper was published addressing all our questions, forcing us to focus on a different topic. In the other project of this thesis, we focused on understanding how mitochondria replicate in neurons. It is assumed that mitochondria are generated in the cell body and travel to the synapse to exert their functions. However, considering the rate of mitochondrial transport in neurons, the time it would take for a single mitochondrion to travel from the cell body to the synapse exceeds the half-life of most mitochondrial proteins. Our goal was to understand whether mitochondrial replication occurred in the periphery of neurons and which mechanisms were involved. We developed a technique to assess mitochondrial replication in mouse primary neuron cultures using 5-bromo-2′- deoxyuridine (BrdU)- and 5-ethynyl-2´-deoxyuridine (EdU)-labelling, two thymidine analogues that are incorporated into mtDNA upon replication. Most BrdU/EdU staining was observed in the cell body, but staining was also present to a lower extent in the periphery. Using microfluidic devices, where axons can be isolated from the cell body, we were able to add EdU only to the axonal side, without interfering with the cell body. In these conditions, EdU staining was only present in axons, confirming that mitochondrial replication in neurons can occur away from the cell body. We hypothesized that mRNA and local translation must be at place in the periphery of neurons in order to provide all the necessary machinery for mitochondria to replicate. To test this, we assessed mitochondrial replication upon inhibition of both nuclear-encoded and mitochondrial-encoded protein translation. Mitochondrial replication in neurons decreased when nuclear-encoded protein translation was inhibited. However, no differences were observed upon inhibition of mitochondrial-encoded protein translation. Taking advantage of the proteomic screen comparing synaptic with non-synaptic mitochondria, two candidate proteins related with protein translation were found upregulated in the synaptic fraction – eukaryotic elongation factor 1 alpha 1 (eEF1a1), involved in nuclear-encoded protein translation; and mitochondrial translation elongation factor Tu (TUFM), involved in mitochondrial-encoded protein translation. We performed loss and gain of function assays with our candidate proteins and assessed their impact on mitochondrial replication. When eEF1A1 was downregulated, we observed a decrease in mitochondrial replication in the periphery of neurons. This effect was rescued by reintroducing eEF1A1. Regarding TUFM, no differences were observed. Our results confirm that mitochondrial replication can occur in the periphery of neurons, and that this process requires nuclear-encoded protein translation, mediated by eEF1A1. Understanding how mitochondrial replication occurs in neurons, particularly at the level of the synapse, provides novel lines of research to tackle the pathophysiological mechanisms underlying neurodegenerative diseases.

2024-04Doctoral thesis

Open access