One of the hottest cellular organelles of the year so far has to be mitochondria. Deleting them has been shown to reverse cellular aging, mitochondria transplants have been shown to reverse pulmonary hypertension, and they are promising targets for developing cures for and understanding neurodegenerative diseases like Parkinson’s, Alzheimer’s and dementia.
To add to the list, scientists the world over are revealing that mitochondrial dysfunction may be a central component of major psychosis (schizophrenia, and in particular bipolar disorder) and perhaps other mental illnesses. Importantly, this means that re-establishing healthy mitochondrial function may be the key to successful treatments and therapies.
Once free-living bacteria that were engulfed by another cell over a billion years ago, mitochondria are now best known as the energy providing powerhouses of our cells. They are also vital to other cellular processes including the formation of reactive oxygen species, cell cycle/growth and survival, balancing calcium ion levels, and neurotransmission.
Multiple lines of scientific evidence indicate that mitochondrial abnormalities and dysfunction are critically involved in psychosis, but what exactly is going on in a cell to create this dysfunction is not yet fully understood.
There are many complex, intertwined molecular pathways that collectively support the healthy functioning of mitochondria, and that is why multiple different abnormalities and mutant molecules can cause mitochondrial dysfunction that impairs neuronal functioning and can cause death of neurons in schizophrenia and bipolar disorder.
Authors of a recent review published in the Canadian Journal of Psychiatry state that:
Bipolar disorder and schizophrenia are complex diseases that cannot be characterized by a singular narrow pathway. Rather, numerous subtle alterations likely converge upon particular pathways (i.e., mitochondrial function) to produce functional alterations.
Some of the earliest points in these mitochondrial function-linked pathways that something could go wrong with and promote psychosis include:
Mutations and altered expression of nuclear and mitochondrial genes
Mitochondria have their own DNA called mtDNA that we inherit from our mothers, and our cells have their own double stranded DNA, one strand inherited from our mother, the other our father. There are many heritable mutations in both mtDNA and DNA that have been reported in bipolar disorder and schizophrenia that can alter mitochondrial function. Similarly, gene-environment interactions, where our life experiences and stresses can epigenetically alter how genes are expressed, have been identified for genes that are necessary for healthy mitochondrial function in people with major psychosis.
- Altered mitochondrial dynamics and trafficking
Initial investigations suggest a role for altered mitochondrial dynamics and trafficking in schizophrenia, although these processes have not yet been extensively explored in schizophrenia or bipolar disorder. Impairment in mitochondrial trafficking (i.e. the movement and localization of mitochondria within neurons) can produce alterations in neurotransmitter release and synaptic function. Impairment in mitochondrial dynamics (i.e. how mitochondria divide and multiply as well as fuse together in the formation of large networks of 1000s of mitochondria per cell) has been suggested to lead to altered neural connectivity.
- Perturbed calcium ion flux and cell signalling
Calcium ions are essential to the synchronization of neuronal electric activity, which is mediated by mitochondria. It also acts as an intracellular signal integral to the functioning of neurons, eliciting responses such as altered gene expression, cell death/survival, cell metabolism and neurotransmitter release at neuronal synapses. It’s a cyclic relationship in the brain of those with psychosis, where disruptions in either mitochondrial function or calcium ion flux have the potential to exacerbate one another. Impairments in calcium signalling can lead to mitochondrial dysfunction, while impairments in mitochondrial function can lead to problems with calcium signalling.
The future: Mitochondria as a target for treating psychosis
Much more intensive research is required to better understand the complex processes involved in the dysfunction of mitochondria in mental disorders, and how treatments can restore their function.
Although not confirmed in patients with psychosis, physical exercise may be one of the best non-pharmacological strategies used to reverse brain dysfunction. Endurance training involves adaptations that can lead to the upregulation of tissue-protective mechanisms, including increased mitochondrial biogenesis and function, and improvement in antioxidant networks, leading to more effective control of free radical production.
Ultimately, further research could lead to the prescription of lifestyle changes, interventions, therapies and even mitochondria-protecting drugs. It may be that by helping restore mitochondrial biogenesis and function, this can improve the chances of successfully treating psychosis, and, if preliminary research findings are valid, perhaps mood disorders and other mental illnesses too.
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