Blast-overpressure induced modulation of PARP-SIRT-NRF2 axis in stress
signaling of astrocytes and microglia.
Abstract
Background: The pathomechanism of blast TBI and blunt TBI is different.
In blast injury, evidence indicate that a single blast exposure can
often manifest long-term neurological impairments. However, its
pathomechanism is still elusive and treatments were symptomatic. Poly
ADP Ribose Polymerase-1 (PARP1) is being implicated in the parthanatos
and secondary neuroinflammation. Animal studies indicate the
over-activation of as a major downstream event underlying the
neurological sequalae of several traumatic and neurodegenerative
disorders irrespective of the mode of cell death. PARP over-activation
forms ADP polymers on several nuclear proteins known as trans-PARylation
by consuming NAD+ and ATP. As NAD+ is a substrate for sirtuins, it too
has been implicated in the oxidative stress underlying TBI pathology.
Hypothesis: We recently established the implication of PARP1 following
blast overpressure (BOP) and its differential response on astrocytes and
microglial cells. We found that the inhibition of PARP is proven to be
beneficial by attenuating oxidative stress. In this study, we
hypothesized the involvement of the PARP1-SIRT-NRF2 axis following Blast
induced PARP over-activation in glial cells for the manifestation of
oxidative stress in BOP insults. Objective: Our objective is to
determine the downstream modulation of the PARP-Sirt-NRF2 axis and
changes in ATP levels following blast exposure in astrocytes and
microglia cell lines. Results: As a result of NAD+ being a common
substrate for PARP1 and Sirtuins, we found the decreased expression of
SIRT1, SIRT3 and NRF2, a major transcriptional regulator for the
expression of antioxidant genes. We found that ATP levels were elevated
post-BOP from both glycolysis and oxidative phosphorylation (OXPHOS), an
increase of ATP by glycolysis more significant than OXPHOS source
indicating the pro-inflammation post-BOP. Conclusion: This result shows
that blast-induced PARP over-activation impacts the deacetylation
activity of sirtuins and consequently impacts the regulation of
antioxidant levels in astrocytes and microglia.