Exploring the neurotrophic effect of pleiotrophin on glial cells
Creators: Gupta, Somnath
Publisher: name: University of Alberta Library
Year: 2024

<p>Recovery after stroke depends on the extent of neuronal regeneration and myelination of<br>
existing and newly differentiated neurons. Regeneration process is governed by various factors<br>
released from glial cells. During an injury, glial cells activate and form a glial scar surrounding the<br>
lesion area. These activated glial cells produce and release various factors, including Chondroitin<br>
sulfate proteoglycans (CSPGs), a component of the extra cellular matrix. CSPGs accumulate in<br>
the glial scar and can modulate activity of adjacent cells including neurons, oligodendrocyte<br>
precursor cells (OPCs), and microglia. CSPGs inhibit the growth of neurons and OPCs and inhibit<br>
the differentiation of OPCs to oligodendrocytes. In this thesis, we examined how the neurotrophic<br>
factor pleiotrophin (PTN) could counteract these inhibitory effects in neurons and glia. We first<br>
tested the hypothesis that PTN can enhance the growth of neurons even in the presence of CSPGs.<br>
Primary cortical neurons cultured on an inhibitory CSPGs matrix exhibited reduced neurite growth<br>
relative to control conditions, but growth was restored with PTN treatment even in the presence of<br>
the inhibitory matrix containing CSPGs. PTN induced a dose-dependent increase in neurite<br>
outgrowth with optimum outgrowth at 15 ng mL-1 PTN (114.8% of neuronal outgrowth relative to<br>
laminin control). The growth-promoting effect of PTN was blocked by inhibiting the activity of<br>
anaplastic lymphoma kinase receptor (ALK) using 10 nM alectinib (ALK receptor antagonist)<br>
(53.59 % of neuronal outgrowth relative to laminin control). Additionally, in the presence of<br>
CSPGs, neurite outgrowth was also restored by activating signaling downstream of ALK via the<br>
protein kinase B pathway (Akt pathway) using SC79 (an Akt activator), with optimum outgrowth<br>
at 5 µM mL-1 PTN (78.43 % of neuronal outgrowth relative to laminin control). Thus, these data<br>
suggest that PTN can restore the neurite outgrowth of neurons on the CSPGs matrix by activating<br>
the protein kinase B pathway through ALK receptor.iii<br>
Neurons with their axons myelinated by oligodendrocytes demonstrate improved signal<br>
conduction efficiency, a crucial factor in the optimal functioning of the nervous system. Moreover,<br>
microglia, as key players in the brain’s immune defense, play a pivotal role in supporting neurons<br>
by monitoring for abnormalities, clearing debris, and contributing to the overall health and<br>
homeostasis of the nervous system. During an injury, CSPGs in the glial scar greatly inhibit<br>
differentiation of OPCs to oligodendrocytes and contribute to the activation of microglia. Here,<br>
we found that PTN can modify the release of pro-inflammatory cytokines from microglia in the<br>
presence of CSPGs. In the absence of inflammatory stimulation with IFN γ, PTN reduced the<br>
expression of pro-inflammatory cytokines. In contrast, PTN potentiated the release of proinflammatory cytokines in the presence of inflammatory stimulus with IFN γ. Thus, the data<br>
suggest that PTN can induce the differentiation of OPCs to oligodendrocytes, enhance the<br>
inflammatory activity of microglia in the presence of IFN γ, and reduce pro-inflammatory<br>
cytokines from microglia in the absence of an inflammatory stimulus.<br>
Astrocytes exert a crucial influence on neurons by maintaining homeostasis, providing<br>
metabolic support, and participating in synaptic regulation, contributing significantly to the overall<br>
well-being and function of the nervous system. During an injury, activated astrocytes release<br>
CSPGs to form the glial scar, but no study to date has measured the effect of PTN on astrocytes in<br>
the presence of CSPGs in vitro. Our data suggest that PTN induces the release of pro-inflammatory<br>
cytokines from astrocytes. To create an environment more closely approximating the in vivo<br>
condition, also examined the effects of PTN on mixed glial cultures consisting of astrocytes,<br>
microglia, and oligodendrocytes in the presence of CSPGs. We found that in the presence of<br>
CSPGs, PTN reduced the expression of pro-inflammatory cytokines from mixed glia. In contrast,<br>
the PTN showed a trend towards increased expression of pro-inflammatory cytokine during coiv<br>
incubation with an inflammatory stimulus. Overall, our data indicates that PTN plays a pivotal role<br>
in modulating the activity of neurons and glial cells in the presence of CSPGs, fostering an<br>
environment that promotes the regeneration of neurons, the differentiation of oligodendrocytes,<br>
and the reduction of neuroinflammation in a manner that is modulated by the inflammatory<br>
activation of these cells. Thus, PTN holds the potential to be considered as a treatment therapy to<br>
enhance the recovery process after brain injury.</p>