生物分子情報研究室

Laboratory of Biomolecular Informatics

理化学研究所 生命機能科学研究センター招へい准教授

Li-Kun PHNG

likun.phng

URL: http://phnglab.riken.jp/index.html

The establishment and maintenance of a networkof blood vessels is crucial throughout the lifetime of avertebrate. During development, blood vessels
supply oxygen and nutrients to meet the demandsof growing tissues such that inadequate blood vessel
formation can lead to embryonic lethality. In theadult, the circulatory network of blood vessels caters
for the metabolic needs of tissues and organs; serveas conduits through which immune cells travel to sites
of infection; and, importantly, new blood vessel
formation is necessary for tissue repair. The formationof new blood vessels frequently occurs throughsprouting angiogenesis, where new vessels are
generated from pre-existing ones. Sprouting
angiogenesis is a multicellular process that is tightly
regulated in time and space beginning with theformation of new vascular sprouts composed ofendothelial cells. Together, endothelial tip and stalkcells migrate in a collective manner to invade
hypoxic tissues. The polarised migration of endothelial cell collectives requires the coordinatedbehaviour of individual endothelial cells that ismediated through cell-cell junctions, which act assites of mechanocoupling to transmit force from one
cell to another. Endothelial cells also undergo
extensive changes in cell shape that is adapted tofunction. Live imaging has revealed that local andtransient cell shape changes underlie migration, cellrearrangements, anastomosis and lumen formation,
which are cellular behaviours that are critical forbuilding a multicellular tubular vascular network.
My lab is interested in understanding the morphogenetic processes of blood vessel formation andmaintenance. Using the zebraﬁsh as a model system,
we employ genetics, molecular biology, optical andpharmacological approaches with high resolution
time-lapse imaging to investigate how endothelial
cell behaviours are regulated and coordinated tobuild vessels of speciﬁc size and architecture.
Endothelial cell shape regulation
Endothelial cells undergo extensive cell shape changes
required to drive speciﬁc cellular processes. In our lab,
we seek to understand how the actin cytoskeleton
regulates endothelial cell shape plasticity. We havepreviously shown that during sprouting angiogenesis, thegeneration of actin bundles in ﬁlopodia facilitates eﬃcient
cell migration and anastomosis (Phng et al., 2013).
During lumen formation, transient polymerization ofactin at the apical membranes controls lumen
expansion (Gebala et al., 2016) while actin cables atendothelial cell-cell junctions stabilize newly-formed

tubules to produce a functional vascular network (Phng etal., 2015). Our work therefore demonstrates that actin
cytoskeleton of diﬀerent dynamics and localization drive
distinct steps of vessel morphogenesis. Future studies in
the lab include understanding how the actomyosin
cytoskeleton is remodelled and organized to generate
specialised subcellular structures that drive cell shapechanges during angiogenesis, and, upon the establishmentof a patent vascular network, how endothelial cells
maintain their shape and the vessel retain its structure.

mechanism by which haemodynamic forces regulate
endothelial cell behaviours to modulate blood vessel
diameter and network pattern is still unresolved. In thisproject, we seek to unravel how haemodynamic forces
remodel endothelial cell actomyosin organization andjunctions to regulate endothelial cell behaviors (such assize and shape) and control blood vessel diameter.

Endothelial cell mechanoresponse tohaemodynamic forces
Once blood vessels become lumenized, endothelial cells
are exposed to haemodynamic forces such as ﬂuid shear
stress and blood pressure. Previous work demonstrates
that blood pressure locally deforms the apical membraneof endothelial cells to generate inverse blebs during lumen
formation (Gebala et al., 2016). In turn, endothelial cells
counteract the deforming forces by triggering an actomyosin-dependent repair mechanism to retract the blebs.
More recently, we discovered that endothelial cells adapt
to increasing haemodynamic forces by generating a cortex
composed of a balanced network of linear and branchedactin bundles that resist ﬂuid forces (Kondrychyn et al.,2020). When the balance of linear and branched actin
bundles is skewed towards linear by the over expressionof the actin bundling protein, Marcksl1, the endothelial cellcortex becomes weaker and more deformable, leading toectopic membrane blebbing and cell enlargement whensubjected to haemodynamic forces. This work thereforehighlights the importance of cortical actin organization inmodulating endothelial cell mechanoresponse to blood
ﬂow to regulate cell and vessel shape. Future work in thelab is aimed at quantifying the types and magnitude of
haemodynamic forces (wall shear stress, luminal pressure)that endothelial cells are exposed to during vesselmorphogenesis using computational ﬂuid dynamics
modelling, and how endothelial cells sense and respond tochanges in haemodynamic forces.

Figure 1.：Blood vascular network in a developing zebraﬁsh embryo

Figure 2. Actin cytoskeleton in a zebraﬁsh intersegmental vessel.

Seeing is believing.

Regulation of vessel remodelling by
blood ﬂow
After the formation of blood vessels, the primitive
vascular network is further remodelled in a blood-ﬂow
dependent manner to generate a hierarchical network oflarger arteries and veins and smaller caliber capillaries of
optimal branching pattern. This is achieved throughalteration in vessel diameter, which requires changes inendothelial cell shape and size, and vessel pruning, whenendothelial cells migrate from a vessel segment with low
blood ﬂow to a segment with higher ﬂow. However, the〒650-0047
兵庫県神戸市中央区港島南町2-2-3C棟N202
理化学研究所 生命機能科学研究センター
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