Background: Understanding the underlying pathogenic mechanisms and identifying disease-modifiers capable of altering the course of Amyotrophic Lateral Sclerosis (ALS) are crucial for the development of new therapies. One such candidate is the WW domain-containing oxidoreductase (WWOX) gene whose role in mitochondrial function, DNA damage repair, and neurodegeneration is widely reported. Specifically, the Short-chain Dehydrogenase/Reductase (SDR) domain of WWOX has been shown to inhibit GSK3 activation, decrease tau phosphorylation, and regulate mitochondrial function.
Objective: To evaluate the role in WWOX in ALS using post-mortem motor cortex samples.
Results: Our genetic analysis in 4,366 ALS samples from Project MinE revealed several rare genetic variants in WWOX which were completely absent in gnomAD. Specifically, our analysis revealed two ALS specific mutations in the SDR domain of WWOX, critical for GSK3 activation, tau phosphorylation, and regulating mitochondrial function. Given that tau hyper-phosphorylation impairs mitochondrial dynamics, we hypothesized that alterations in WWOX function may lead to an increase in GSK3 activity and tau phosphorylation and, in turn, to mitochondrial dysfunction in ALS. As predicted, there was a significant decrease in WWOX levels in post-mortem ALS motor cortex (mCTX) compared to controls as measured by western blots. To determine whether GSK3activity and tau phosphorylation were altered in ALS, we assessed the levels of these proteins in three different cellular fractions in human post-mortem mCTX (total, cytosolic, and synaptoneurosomes (SNs) fractions) using western blots. Our results demonstrated that while there was a significant increase in phosphorylated GSK3 and tau in ALS SNs, WWOX levels were significantly decreased. Next, we assessed mitochondrial dynamics by evaluating proteins that are important for fusion and fission of mitochondria. Western blot analysis in post-mortem mCTX revealed that while there was a significant increase in dynamin related protein 1, there was no change in mitofusion 1 or 2 in the SNs from ALS compared to control.
Conclusions: Together, these findings provide a potential novel mechanism in ALS involving WWOX/GSK3/tau signaling. Specifically, our study demonstrates that a loss of WWOX may lead to phospho-tau mis-localization and an increase in mitochondrial fission in ALS.