Exploring the neurotrophic effect of pleiotrophin on glial cells

• Author / Creator

  Gupta, Somnath

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

• Subjects / Keywords

  • Neurons
  • microglia
  • pleiotrophin
  • Oligodendrocytes

• Graduation date

  Spring 2024

• Type of Item

  Thesis

• Degree

  Doctor of Philosophy

• DOI

  https://doi.org/10.7939/r3-dx6q-tn95

• License

  This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.