This paper discusses neuroinflammation as a cause for
Parkinson’s disease. The study goes over inflammation that is caused by
microglia activation, ROS production, and cytotoxicity. The purpose of this
study is to investigate the ability of regulatory T cells (Treg) to influence neuroinflammation
that causes dopaminergic neuron degradation in the substantia nigra pars
compacta region of the brain. The loss
of dopaminergic neurons is the cause for loss in control of muscle movement and
balance seen in Parkinson’s disease. The paper discusses oxidative stress and
microglia activation as potential causes for the up regulation in
neuroinflammation. The activation of microglia is shown to release secretory
factors such as TNF-α and iNOS which stimulate dopaminergic cell loss through
inflammation. The data collected from the study show that Treg have the ability
to attenuate neuroinflammation and support neuronal growth. Although the exact
mechanism of how Tregs operate remains unclear, the commonly accepted
hypothesis is the interaction between Tregs and local glial cells. As Tregs are
directed into the brain, they are able to interact with local glial cells and
this interaction causes toxic microglia to change into a trophic state which
reduces the release of inflammatory factors. The study suggests two possible
reasons for why Tregs are able to suppress the inflammatory responses from
activated microglia. After doing a RT-PCR (reverse transcription polymerase chain
reaction) on Treg, it showed that Treg has high mRNA expressions of IL10 and
TGF-β.
IL10 is an anti-inflammatory cytokine which is able to protect against
inflammation-mediated degeneration of neurons, inhibit proinflammatory cytokine
production, and increase Treg. TGF-β inhibits the activation of microglia
and induction of inflammation. It has also been shown to provide neuroprotection.
Not only are Tregs able to inhibit the release of inflammatory factors from
microglia, they also support neuronal growth by inducing the synthesis of
astrocytes. Astrocytes provide physical support for neurons and clean up
debris. When Tregs are present, certain astrocyte-derived neurotrophic factors such
as BDNF and GDNF are expressed. These neurotrophic factors are required for the
synthesis of astrocytes.
The study includes three experiments which look at how
Tregs modulate neuroinflammation. The first and second experiments are
conducted using MPTP-intoxicated mice while the third experiment is conducted
using MES23.5 cells. MPTP is a precursor to the active compound MPP+ and the
change from MPTP to MPP+ is dependent on astroglial transformation. The active
compound MPP+ is a neurotoxin that causes permanent symptoms of Parkinson’s
disease. The MES23.5 cell is a dopaminergic line cell which resembles cells of
dopaminergic neurons. The mice used for the first and second experiment are SJL
mice which are mice with weakened muscles and made to resemble the muscles of
someone who has Parkinson’s disease or multiple sclerosis.
Within each experiment, there are control groups with and
without neuroinflammation. The groups with neuroinflammation also receive adoptive
transfers of Treg or Teff (effector T cells). The isolated T cells are transferred
from identical mice that have not been introduced to neuroinflammation. In
order to identify Treg and Teff, RT-PCR is done to look for certain mRNA
expression that can only be found on either Treg or Teff. A clear indicator of
Treg is the mRNA expression of Foxp3 which is an essential transcription factor
required for Treg development and function. Treg show high expression of Foxp3,
IL10, and TGF-β while Teff show high expression of IFN-ϒ.
The first experiment shows that Treg is able to reduce
inflammation caused by MPTP. When compared to the controls and MPTP with
adoptive transfer of Teff, the adoptive transfer of Treg with MPTP has the greatest
decrease in Mac-1 antigen expression which is the indicator for inflammation in
this experiment. The second experiment shows that Treg is neuroprotective and support
neuronal growth. Adoptive transfer of Treg with MPTP is able to sustain a
larger number of dopaminergic neurons compared with the other groups. The
second experiment also shows that neuroprotection from Treg is dose-dependent
and only affects dopaminergic neurons. The third experiment shows that Treg is
able to reduce the amount of ROS production and cytotoxicity that is caused by
the activation of microglia. In the third experiment, Treg and Teff were
cocultured with stimulated microglia and were compared with unstimulated
microglia and stimulated microglia without Treg or Teff. The Treg cocultured
with stimulated microglia shows a significant decrease in the amount of ROS
production and level of cytotoxicity. Data collected from all three experiments
demonstrate the importance of regulatory T cells and how they play a large role
in modulating immune responses. This is a great area for further research
because Treg is able to significantly attenuate neuroinflammation which is
hypothesized to be one of the main causes of Parkinson’s disease. The
anti-inflammatory cytokines associated with Treg should also be considered in
the future of Parkinson’s disease research. Overall, this study was fairly
technical and difficult to read, but it provides a deep understanding of the
disease and potential treatments.
Although, the study was conducted with mice and over a short
period of seven days, do you think the data collected is strong enough to
support regulatory T cell therapy or would more research in this area need to
be done?
How might regulatory T cell therapy be accomplished?
Link to Study
http://www.jleukbio.org/content/82/5/1083.full
Well done with a difficult article. I think this article joins the many we have discussed this semester as "good information...but requires more research". Major limitations including the length of the study, not being performed on humans and the fact that the disease was artificially induced makes for a poor case to advance into a clinical setting. I think there is a promising future in T cell therapy and PD; however, discovery of the fundamental mechanisms of dysfunction are vital for more promising interventions.
ReplyDeleteNonetheless, we mentioned in class the importance of the hippocampus in PD patients because it is the brain area for memory and learning. It has been found that some of the non-motor symptoms associated with PD are often present at the time of diagnosis and can precede motor symptoms. With this in mind, I wonder if T cell therapy that can detect/treat early signs of dysfunction (such as inflammatory cytokines from α-Synuclein/α-Syn proteins) would be a better use of research money?