Neuronal Exosomal miR-124 Regulation of Glutamate Uptake
Abstract: Exosomes have been recently touted as a novel form of intracellular
communication, and of great excitement as there may be variability of the types of cells
that release exosomes, exosomal contents, and the specificity of the recipient cells,
particularly in disease states. This combined with the possibility that exosomes can be
secreted from central nervous system tissues into the c... read moreerebrospinal fluid or blood in the
periphery suggests that exosomes may also be examined for insight into dysregulation of the
host tissue. However, from the myriad of studies observing altered exosomal content in
disease states, we remain unable to determine the exosomal host cell or the functional
implications of their altered cargo. One of the few studies successfully aimed to answer
these questions was published prior to my tenure in the Yang Lab, where authors observed
that neurons release a high abundance of microRNA-124, of which is capable of upregulating
glutamate transporter expression in astrocytes. The purpose of my thesis has been to
further investigate this mechanism, and determine if it is altered in a neurological
disease state. In my first publication, my colleagues and I have characterized a novel
cre-dependent CD63-eGFP transgenic mouse, which allowed us to observe extracellular vesicle
behavior for the first time in vivo. We show that neurons release an abundance of exosomes
which are internalized into glia, and that these exosomes contain distinct microRNA
profiles. Compellingly, we found that blockade of exosome biogenesis led to a reduction of
glutamate transporter expression in astrocytes, mediated in part by the loss of
neuronally-delivered miR-124. I further characterized a mechanism where miR-124 inhibits
the expression of downstream microRNAs miR-132 and miR-218, both of which inhibit GLT1
protein expression. Utilizing our now-characterized CD63-eGFP mouse, I was then able to
explore this miR-124-mediated mechanism in a mouse model for amyotrophic lateral sclerosis
(ALS), SOD1G93A for my second publication. I found increased association of miR-124 with
CD63-eGFP, suggesting that miR-124 is increasingly packaged into extracellular vesicles
released from diseased SOD1G93A motor neurons. I found that indeed, there is also a loss of
miR-124 expression from diseased motor neurons, as well as increased secretion of miR-124
into astrocytes. However, examination of SOD1G93A astrocytes treated with a miR-124 mimic
revealed that while there is increased internalization of miR-124 into astrocytes in vivo,
miR-124 is incapable of restoring GLT1 protein expression. Taken together, these two bodies
of work provide ample characterization of our CD63-eGFP transgenic mouse, which will allow
the scientific community to further investigate the role of extracellular vesicles in vivo.
I have also shown that neuronal exosomal miR-124 is necessary for maintaining appropriate
levels of GLT1 in non-diseased tissue, as well as that this mechanism is perturbed in an
ALS disease state, potentially participating in ALS disease pathology.
Thesis (Ph.D.)--Tufts University, 2018.
Submitted to the Dept. of Cell, Molecular & Developmental Biology.
Advisor: Yongjie Yang.
Committee: Rob Jackson, Peter Juo, and Larry Feig.
Keywords: Neurosciences, Molecular biology, and Developmental biology.read less