Biomedical Engineering Reference
In-Depth Information
targeted antagonist that could be used in disease states where
NRG1 signaling is deleterious as well as a useful research
tool to study NRG1's multiple critical functions during
development [79]. We and others have shown that NRG1
signaling is critical for Schwann cell survival during devel-
opment. Using the HBD-S-H4 antagonist, we show a
marked increase in Schwann cell apoptosis precisely in
the regions where HBD-S-H4 becomes concentrated (as
shown in Figure 27.5). We also found that Schwann cell
differentiation from precursors to more mature stages was
inhibited in both motor and sensory axons with HBD-S-H4,
suggesting NRG1 is a critical survival and differentiation
factor required for Schwann cell normal development (data
not shown).
Since the fusion protein successfully targets NRG1 sig-
naling in vivo during development, we next asked whether
this completely humanized fusion protein could be useful
therapeutically in disease models. We found that as some
human breast epithelial cells become more malignant, they
develop autocrine NRG1 signaling that promotes prolifera-
tion [1,2]. When the antagonist HBD-S-H4 was applied to a
highly malignant breast cancer cell line, the fusion protein
significantly decreased both autocrine phospohorylation as
well as cell proliferation rate similar to Herceptin [79]
(Figure 27.6). In vivo, HBD-S-H4 has been used to block
NRG1 signaling in a rat model of chronic pain [83,84].
NRG1 promotes microglial proliferation and chemotaxis
that directly contributes to the development of neuropathic
pain after sciatic nerve injury. Intrathecal injection of HBD-
S-H4 in these rats significantly reduced microglial cell
proliferation and significantly reduced pain-related behav-
iors including mechanical pain hypersensitivity and cold
allodynia.
27.11 CONCLUSIONS AND FUTURE
PERSPECTIVES
FIGURE 27.5
HBD-S-H4 targets to the same regions of the
developing nervous system where NRG accumulates. (A) 20
m
gof
HBD-S-H4 was added to the chorioallantoic membrane of embry-
onic chicken embryos. Tissue sections through the spinal cord
2 days later at embryonic day 7 show a comparison between
endogenous chicken NRG expression (green, left) and HBD-S-H4
distribution (green, right) at low power (top). Higher power images
(bottom panel) focusing on the spinal cord show that HBD-S-H4
adhered to the same regions as endogenous NRG along axonal tracts
in the spinal cord (arrows) and along the ventral nerve root (arrow-
head). Sections were counterstained for nuclei with DAPI (blue).
Scale bars are 200
m
m. (B) Both endogenous chicken NRG (chNRG,
green) and HBD-S-H4 (huNRG, green) were concentrated in the
ventral nerve root identified by a Schwann cell marker (red). High
salt (1M NaCl for 1.5 h) treatment on sections of HBD-S-H4
removed the signal in the ventral root. Control treatments with saline
did not reveal any immunoreactivity with the same antibody in the
ventral nerve root. Scale bar is 50
m
m. Source: This research was
originally published in J. Biol. Chem. Reference 79.
HSPGs give tissue surfaces a unique molecular signature
due to their diversity in both core protein and GAG struc-
tures. This diversity is regulated by highly specific enzymes
that regulate their synthesis and modifications through post-
translational processing. This result means for a given cell-
surface region to become receptive to specific growth and
differentiation factors in a spatially and temporally regulated
manner. In addition to growth factors, cytokines, and che-
mokines, virus have also evolved to use this natural delivery
system with the emergence of a number of structurally
distinct HBDs.
We and others have taken advantage of this natural-
targeting system using a strategy of generating fusion pro-
teins with naturally occurring or engineered HBDs to guide
biopharmaceuticals to achieve local delivery and to mini-
mize systematic side effects at the same time. NRG1's HBD
Search WWH ::
Custom Search