CS Delaveris, CL Wang, NM Riley, S Li, RU Kulkarni, CR Bertozzi
ACS Central Science (2023)
Neurons communicate with each other through electrochemical transmission at synapses.
Microglia, the resident immune cells of the central nervous system, modulate this
communication through a variety of contact-dependent and -independent means. Microglial
secretion of active sialidase enzymes upon exposure to inflammatory stimuli is one
unexplored mechanism of modulation. Recent work from our lab showed that treatment of
neurons with bacterial sialidases disrupts neuronal network connectivity. Here, we find
that activated microglia secrete neuraminidase-3 (Neu3) associated with fusogenic
extracellular vesicles. Furthermore, we show that Neu3 mediates contact-independent
disruption of neuronal network synchronicity through neuronal glycocalyx remodeling.
We observe that NEU3 is transcriptionally upregulated upon exposure to inflammatory
stimuli and that a genetic knockout of NEU3 abrogates the sialidase activity of
inflammatory microglial secretions. Moreover, we demonstrate that Neu3 is associated
with a subpopulation of extracellular vesicles, possibly exosomes, that are secreted
by microglia upon inflammatory insult. Finally, we demonstrate that Neu3 is necessary
and sufficient to both desialylate neurons and decrease neuronal network connectivity.
These results implicate Neu3 in remodeling of the glycocalyx leading to aberrant
network-level activity of neurons, with implications in neuroinflammatory diseases
such as Parkinson's disease and Alzheimer's disease.
RU Kulkarni, CL Wang, CR Bertozzi
PLoS Computational Biology (2022)
While hierarchical experimental designs are near-ubiquitous in
neuroscience and biomedical research, researchers often do not
take the structure of their datasets into account while performing
statistical hypothesis tests. We present Hierarch, a Python package for
analyzing nested experimental designs. Using a combination of permutation
resampling and bootstrap aggregation, Hierarch can be used to
perform hypothesis tests that maintain nominal Type I error rates
and generate confidence intervals that maintain the nominal
coverage probability without making distributional assumptions
about the dataset of interest.
RU Kulkarni, DJ Kramer, N Pourmandi, K Karbasi, HS Bateup, EW Miller
Proceedings of the National Academy of Sciences (2017)
We have designed, synthesized, and applied a rhodol-based chromophore to a molecular
wire-based platform for voltage sensing to achieve fast, sensitive, and bright voltage
sensing using two-photon (2P) illumination. Rhodol VoltageFluor-5 (RVF5) is a
voltage-sensitive dye with improved 2P cross-section for use in thick tissue or brain
samples. RVF5 features a dichlororhodol core with pyrrolidyl substitution at the
nitrogen center. In mammalian cells under one-photon (1P) illumination, RVF5
demonstrates high voltage sensitivity (28% ΔF/F per 100 mV) and improved photostability
relative to first-generation voltage sensors. This photostability enables multisite
optical recordings from neurons lacking tuberous sclerosis complex 1, Tsc1, in a mouse
model of genetic epilepsy. Using RVF5, we show that Tsc1 KO neurons exhibit increased
activity relative to wild-type neurons and additionally show that the proportion of
active neurons in the network increases with the loss of Tsc1. The high photostability
and voltage sensitivity of RVF5 is recapitulated under 2P illumination. Finally, the
ability to chemically tune the 2P absorption profile through the use of rhodol scaffolds
affords the unique opportunity to image neuronal voltage changes in acutely prepared
mouse brain slices using 2P illumination. Stimulation of the mouse hippocampus evoked
spiking activity that was readily discerned with bath-applied RVF5, demonstrating the
utility of RVF5 and molecular wire-based voltage sensors with 2P-optimized fluorophores
for imaging voltage in intact brain tissue.