Targeting mitochondrial fusion to alleviate brain injury in infants

Restricted blood flow/oxygen to the brain occurs during the birth of 2-3 babies per 1000 in the UK and depending on the severity, can result in permanent, life-long brain injury including cerebral palsy. The emotional, social and financial burdens to the children and their families is considerable and our work focuses on developing therapies to ameliorate the consequences of this devastating injury.

Following initial injury during birth, there is a delay of a few hours before the majority of brain cell death occurs and this delay provides clinicians with a valuable treatment window. Currently the only available treatment is therapeutic hypothermia, in which the body temperature of the baby lowered for three days. When hypothermia is initiated rapidly after birth, it can double the chances of survival without brain injury. Unfortunately, it is only successful for 1 in 7 neonates, but it proves that we can intervene with therapy following injury and still produce an effective outcome. This is critical because as yet we cannot predict in advance which babies will suffer brain injury.

Mitochondria reside inside all cells in the body (except red blood cells), and function to generate cellular energy needed for survival. Brain injury and brain cell death occurs when cellular energy falls to extremely low levels. Therefore, although many events are triggered after the insult, we believe that mitochondria act as a hub where all these events converge. Following the initial insult, the outer mitochondrial membrane becomes leaky, releasing mitochondrial contents into the cell and in doing so, committing the cell to death. At the same time, the inner mitochondrial membrane becomes disrupted, freeing pro-death molecules normally held securely within the folds of the inner membrane.

OPA1 is a mitochondrial protein which acts as a "molecular staple" holding together the folds of the inner mitochondrial membrane. Data from our animal model shows that unfortunately, OPA1 becomes degraded after the birth injury. We predict that if we protect the integrity of OPA1, we will provide mitochondria with additional defences to resist releasing pro-death molecules, and continue to feed the cell with the energy it needs to stay alive.

We will perform research in our animal model and in a variety of cultured brain cells to evaluate the impact of OPA1 degeneration on brain injury. We will also identify new mechanisms which might contribute to the degradation of OPA1, thus providing novel targets for future drug development. Finally we have the opportunity to use mitochondrial biology to develop a new, non-invasive and early detection method to identify how severely an infant's brain has been injured. By taking this combination of approaches, we aim not only to increase our knowledge of OPA1 biology, but also to use it to our advantage in developing drugs and new tools to improve the outcome of babies at risk of developing lifelong neurological impairment.

Moderate to severe hypoxic-ischaemic (HI) encephalopathy, caused by birth asphyxia in term babies, affects 1-2 in every 1000 live births in the UK and far more in low-to-middle income countries. Therapeutic hypothermia represents the only intervention currently available for these infants and it is not universally successful. We therefore urgently require additional synergistic therapies in order to prevent the devastating life-long consequences which afflict this cohort.

We recently found mitochondrial Optic Atrophy (OPA)1, is rapidly degraded following neonatal hypoxia-ischaemia (HI) in our rodent model, accompanied by increased mitochondrial fission. In vitro, OPA1 inhibition results in increased cellular vulnerability to oxygen-glucose deprivation. We propose that enhancing OPA1 integrity will provide additional neuroprotection for infants where therapeutic hypothermia alone is inadequate.

Aim 1 will use mice with mild OPA1 overexpression to show that OPA1 integrity provides neuroprotection following HI in vivo. Histological analyses of infarct will be correlated with OPA1 integrity. Longitudinal in vivo spectroscopy and behavioural outcomes will determine the metabolic profile for OPA1-mediated survival benefits. Aim 2 will investigate the endogenous regulation of OPA1 in neurons and astroglia cells through a known target approach as well as by RNASeq and metabolomics to determine OPA1-mediated gene networks and metabolic profiles. Finally Aim 3 will investigate a novel, non-invasive diagnostic biomarker in order to stratify the severity of neonatal hypoxic-ischaemic brain injury and which we will validate using gold standard MRI.

This project aims to produce a wide range of much needed resources and tools for use in both basic and translational OPA1 biology, instrumental in improving the outcome of term babies at risk of developing lifelong neurological impairment.

Worldwide, neonatal asphyxia was found to be the second most common cause of death and disability in children under the age of 5 years in 2010, resulting in the loss of 50 million Disease Adjusted Life Years (DALYs) due to long-term neurological dysfunction. The goal of our research is to ameliorate the devastating consequences of perinatal brain injury, which places a huge emotional, social and financial burden on children and their families. Currently only one treatment, therapeutic hypothermia, exists for term hypoxia-ischaemia (HI), which saves 1 out of every 7 infants from development of cerebral palsy or death. Thus, there is a clear, critical unmet need, but hypothermia treatment proves that effective intervention post-injury is achievable.

Impacts from this project will therefore be wide-ranging. These include, but are not limited to clinicians and scientists working in the fields of perinatal brain injury, metabolism, fetal medicine, neurology and neonatology. Scientists with an interest in mitochondrial biology will benefit from the availability of cell type-specific transcriptomics and metabolomics datasets. The development of a method of stratifying brain injury in moderate to severely affected infants will be of specific interest to clinicians working in the Neonatal ICU to aid in subsequent treatment management.

Equally, this research will also impact patients' families as, in the process of defining the regulation of OPA1, we will identify potential druggable targets for either new or repurposed therapy development. Development of such mitochondrial based-therapeutics will not only have a have a societal impact, reducing emotional burden on families but ultimately have economic impact, reducing the costs of long term care for these infants. Finally we predict that successful outcome of this project will impact industry partners both at a pharmacological level as well as through device development. For further information as to how these impacts will be managed, please refer to our "Pathways to Impact" attachment.