YSM Issue 97.1

FOCUS
Biochemistry
How Firefighters Fight the Fire
While much remains unknown about
how neutrophils produce extracellular
glycoRNA, biologists know that neutrophils
aren’t recruited until they are needed.
When tissue is injured or inflamed, it must
somehow signal for neutrophils to come and
bind to the tissue. Lu likens this process of
neutrophil recruitment to firefighters rushing
to a fire. Upon injury, damaged cells release
proinflammatory proteins called cytokines
that signal nearby endothelial cells to express
selectins, like P-selectin, which are normally
tightly controlled. This “fire” prompts the
neutrophils, acting as firefighters, to attend
to the site of injury. “Selectins are like glue
that try to capture circulating white blood
cells—mostly neutrophils because of their
abundance—which starts the neutrophil
infiltration process,” Wu said. P-selectin–
neutrophil–glycoRNA binding is central to
this glue-like interaction, but this is likely just
part of the picture.
Wu and Lu performed an experiment called
RNA sequencing on glycoRNA isolated using
click chemistry from three kinds of neutrophils
in the mouse bloodstream and several human
cell lines. Analyzing the mapping of these
RNAs to the mouse or human genomes
indicated specific rules that could govern
RNA glycosylation. Lu describes these rules
as a “licensing step.” Although the existence
of these rules is not currently known, Lu
speculates that they may involve special RNA
sequences, structures, or modifications. Wu
expressed that it may not be sufficient for an
RNA to be glycosylated for recognition by the
P-selectin; P-selectin’s specificity may include
the RNA as well. These discoveries are only
the first steps in characterizing the specificity
of the P-selectin-neutrophil-glycoRNA
interaction, but the methodology used in this
study will likely inform future explorations of
extracellular protein-glycoRNA interactions
across the body.
PHOTOGRAPHY BY EMILY POAG
Ningning Zhang (left) and Wenwen Tang (right) discuss
an image shown on the computer screen.
How Did GlycoRNAs Get Outside of
the Cell?
The authors proposed two potential
models to explain the mechanism by which
glycoRNAs moved from the cytoplasm inside
the cell to the outer surface of neutrophils.
In the cell-to-cell model, cellular RNAs are
released from one cell and are captured on an
adjacent cell’s surface. On the other hand, in
the cell-autonomous model, the production
and transport of cellular RNAs to the cell
surface occur in the same cell. To differentiate
between these models, a co-culture experiment
was conducted. One group of neutrophils was
labeled with the Ac4ManNAz sugar and a
fluorescent green dye, while another group was
only labeled with a fluorescent red dye. These
cells were then mixed and incubated together.
Afterward, the researchers found only strong
fluorescent signals in the green cells but not
the red cells, confirming the second cellautonomous
model of the production and
transportation of glycoRNAs across the
cell membrane.
Once they had confirmed the cellular
origin of glycoRNAs, Lu and Wu began to
consider the pathways by which glycoRNAs
could leave the cells. One such pathway
was inspired by the C. elegans worm. In this
model organism, the Sidt1 gene was found to
encode RNA transporters that facilitated the
uptake of digested RNA in the gut into the
cells of the worm across cellular membranes.
Therefore, the Yale scientists reasoned that the
Sidt genes expressed in neutrophils could be
facilitating the transport of RNAs across the
cell membrane. To test this hypothesis, they
ABOUT THE
AUTHORS
disrupted the expression of both Sidt1 and
Sidt2 in cells in a knockdown experiment. As
a result, the presence of Ac4ManNAz-labeled
glycoRNAs was abolished, highlighting the
crucial role of Sidt RNA transporters in the
presence of glycoRNAs in cells. Importantly,
the Sidt-knockdown cells also exhibited a
significant reduction in in vivo recruitment
to inflammatory sites, underscoring the
essential role of Sidt genes in the functionality
of neutrophils.
The Future of the RNA World
This novel collaboration between a
neutrophil biologist and an RNA biologist is
only the beginning of a growing field focused
on glycoRNA interactions outside the cell.
Lu and Wu are both eager to continue their
collaboration and begin answering the many
questions opened by this paper. As this field
is still in its infancy, Lu suggests that it will
take some work to even begin elucidating
the initial mechanistic questions, such as
exploring the molecular pathways involved
in making extracellular glycosylated RNAs
and figuring out the environments in which
they are selectively produced or glycosylated.
“We can’t work on all of these questions,
so we have to be careful about picking the
lower-hanging fruits first to work on. Then,
I expect many people will start to work on
it,” Lu said. After that, Wu and Lu hope other
labs explore more disease-specific questions,
like studying the disease conditions in which
these RNAs are dysregulated and whether
there are any therapeutic or diagnostic roles
for extracellular RNAs. ■
KENNY CHENG
RISHA CHAKRABORTY
KENNY CHENG is a first-year student majoring in Molecular, Cellular, and Developmental Biology in
Pauli Murray College. Outside of YSM, Kenny carries out research on ornate, large, extremophilic (OLE)
RNAs in the Breaker lab and is an editorial associate for the Yale School of Medicine and the Yale
Medicine Magazine.
RISHA CHAKRABORTY is a third-year Neuroscience and Chemistry major in Saybrook College. In
addition to writing for YSM, Risha plays trumpet for the Yale Precision Marching Band and La Orquesta
Tertulia, volunteers at YNHH, and researches Parkinson’s Disease at the Chandra lab in the Yale School of
Medicine. She enjoys cracking jokes, having “philosophical” discussions with her friends, and having boba
with her PLees at the Asian American Cultural Center.
THE AUTHORS WOULD LIKE TO THANK Dr. Jun Lu and Dr. Dan Wu for their time and enthusiasm
for their research.
FURTHER READING:
Zhang, N., Tang, W., Torres, L., Wang, X., Ajaj, Y., Zhu, L., Luan, Y., Zhou, H., Wang, Y., Zhang, D., Kurbatov,
V., Khan, S. A., Kumar, P., Hidalgo, A., Wu, D., & Lu, J. (2024). Cell surface RNAs control neutrophil
recruitment. Cell, 187(4): 846-860. https://doi.org/10.1016/j.cell.2023.12.033
24 Yale Scientific Magazine March 2024