Investigation into the destructive and adaptive responses of neural cells to stress
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Hasel2017.docx (37.65Mb)
Date
07/07/2017Author
Hasel, Philip
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Abstract
Homeostasis within the neuro-glial unit is essential to the longevity of neurons.
Conversely, loss of homeostasis, particularly of Ca2+ levels, of redox balance and of
ATP, contribute to neuronal loss and dysfunction in many neurodegenerative and
neurological disorders. This thesis is centred on better understanding the
vulnerability of neurons to stress, as well as adaptive responses to these stresses.
Since neurodegenerative conditions associated with Ca2+, redox and bioenergetic
dyshomeostasis are often characterised by early dendritic pathology, I first studied
dendritic vs. somatic responses of primary cortical neurons to these types of
challenges in real-time. Using a wide range of genetically-encoded probes to
measure Ca2+, ATP, NADH, glutathione and glutamate, I show that dendrites are
selectively vulnerable to oxidative stress, excitotoxicity as well as to metabolic
demand induced by action potential (AP) burst activity. However, I provide evidence
that neurons undergoing energetically demanding AP burst activity can adjust their
metabolic output by increasing mitochondrial NADH production in a manner
dependent on the mitochondrial calcium uniporter (MCU), as well as increase their
capacity to buffer their intracellular redox balance. Finally, I have studied
transcriptional programs in astrocytes triggered by neurons and neuronal activity to
better understand adaptive signaling between different cell types in the neuro-glial
unit. I developed a novel system combining neurons and astrocytes from closely-related
species, followed by RNA-seq and in silico read sorting. I uncovered a
program of neuron-induced astrocytic gene expression which drives and maintains
astrocytic maturity and neurotransmitter uptake function. In addition I identified a
novel form of synapse-to-nucleus signaling, mediated by glutamatergic activity and
acutely regulating diverse astrocytic genes involved in astrocyte-neuron metabolic
coupling. Of note, neuronal activity co-ordinately induced astrocytic genes involved
in astrocyte-to-neuron thyroid hormone signaling, extracellular antioxidant defences,
and the astrocyte-neuron lactate shuttle, suggesting that this non cell-autonomous
signaling may form part of the homeostatic machinery within the neuro-glial unit.