Our lab has several projects in progress simultaneously.
Each lab member typically takes the lead on one project, but all projects
are discussed at weekly lab meetings. All projects use classical molecular
biology techniques such as RT-PCR, western blotting, in situ hybridization,
immunohistochemistry, electron microscopy, and tissue culture; many
projects also involve clinical techniques such as electrophysiology.
The mixture of clinical and basic science approaches aims to correlate
molecular etiologies with clinical applicability.
The Role of Neural Wound Healing in the pathogenesis of Chronic
Nerve Compression to explain why Surgery may not be enough
Chronic nerve compression (CNC) injuries such as carpal tunnel
syndrome cause patients significant morbidity with the ensuing
loss of sensation and motor function. Recent advancements have
prompted a reinterpretation of compressive neuropathies as
possibly an example of a wound healing model consisting of
inflammation, angiogenesis, cellular proliferation, and connective
tissue remodeling. Previous studies have demonstrated the prevalence
of tissue inflammation, increased neural vasculature, and Schwann
cell proliferation during the progression of CNC injury. Because
little is known about the ECM composition in human neuropathies,
their potential role to favor or impede nerve repair in human
disorders remains largely unexplained. We proposed that the
extracellular matrix of peripheral nerves undergoes extensive
modification following CNC injury and may emulate biologic
processes similar to classic wound healing. Our preliminary
results demonstrate CNC injury induces a progressive and significant
increase in ECM components such as fibronectin, laminin, and
collagen type IV at the level of mRNA transcription and protein
translation. Furthermore, we were able to localize their up-regulation
to the site of CNC injury compared to control mice supporting
the hypothesis that CNC injury does induce ECM remodeling.
In contradistinction to chronic constriction injury, CNC injury
also does not up-regulate TNF-alpha at the site of compression.
By considering the pattern of ECM expression with our quantitative
and qualitative findings in two different animal models for
CNC injury, there is a sequence of events involved in the connective
tissue remodeling process that appears to be neural wound healing.
CNC injury seems to stimulate a biologic response that mimics
canonical wound healing and leads to up-regulation of ECM components,
such as laminin, collagen, and fibronectin, with eventual scar
formation. This pathway favors tissue repair by structural
support and restricts the capacity for functional tissue and
nerve regeneration after remodeling takes place.
Click below for larger image.
Desert Hedgehog has a Neuroprotective Effect Against Mechanical
Defining the molecular mechanisms underlying chronic compressive
neuropathies (CNC) is crucial for identifying novel treatment
methods. Desert hedgehog (dhh) is a Schwann cell produced protein
responsible for formation of nerve perineurium. We hypothesize
that it is a potential therapeutic target, given its interaction
with extracellular matrix and connective tissue. Desert hedgehog
deficiency appears to accentuate peripheral nerve demyelination
in chronic compression neuropathies, signifying a vital role
for dhh in the propagation of nerve impulses.
MMP-3 Inhibition Preserves the Motor Endplate after Traumatic
Traumatic Peripheral Nerve Injuries often produce significant
functional deficits despite optimal medical management. Denervation
likely alters the environment that sustains the motor end plate,
leading to end-organ atrophy of the neuromuscular junction(NMJ).
Assembly and maintenance of the NMJ depends highly on interaction
between agrin and muscle-specific kinase(MuSK). Agrin, in turn,
is degraded by Schwann cell-derived matrix metalloproteinase
3(MMP-3). The current study focuses on assessing the NMJ after
long-term denervation in both wildtype and MMP-3 null mice
and investigates whether the NMJ may be stabilized by agrin
overexpression secondary to knockout of MMP-3. To date, there
is not study that has rigorously investigated the role of agrin
in the maintenance of the NMJ following long-term denervation
injury. Given the evidence that agrin is closely linked to
the integrity of the NMJ, the present study aims to determine
whether the stability of the post-synaptic apparatus after
prolonged denervation is improved in MMP-e null mice in contrast
to the wildtype phenotype.
Our preliminary results show that wildtype muscle following
denervation demonstrated significant attenuation in acetylcholine
receptor area as well as a pattern of conversion to an immature
receptor phenotype, particularly at later time points. Surprisingly,
receptors in MMP-3 knockout muscles showed less decrease in
area from baseline. In addition, agrin and MUSK immunoreactivity
remained at acetylcholine receptors late after denervation
injury in MMP-3 null mice whereas expression for these proteins
progressively disappeared in the wildtype animals. Western
blot data revealed an increase in expression in agrin in both
animal groups after injury but also a larger decrease in MuSK
phosphorylation in wildtype mice.
Click below for larger image.