Nmnat Delays Axonal Degeneration Caused by Mitochondrial and Oxidative Stress

“Mitochondrial dysfunction caused by mutations or toxic agents has been implicated in many neurodegenerative diseases, including those associated with axonal degeneration (Lin and Beal, 2006).”

“, DJ-1 and PINK-1) (Martin, 2006) and ingestion of 1-methyl 4-phenyl 1,2,3,6-tetrahydropyridine (MPTP), an inhibitor of mitochondrial complex I (Langston et al., 1983; Betarbet et al., 2000).”

“…Parkinson’s disease (PD), which can be associated with mutations in mitochondria-associated proteins (e.g., DJ-1 and PINK-1) (Martin, 2006) and ingestion of 1-methyl 4-phenyl 1,2,3,6-tetrahydropyridine (MPTP), an inhibitor of mitochondrial complex I (Langston et al., 1983; Betarbet et al., 2000).”

“…chronic rotenone model of PD, which more closely mimics the degenerative progression observed in PD patients, because this model only works in rats (Hornykiewicz, 1966; Betarbet et al., 2000; Richter et al., 2007); however, our results suggest that increasing Nmnat expression in this model may…”

“The suppression of ROS accumulation by Nmnat proteins is reminiscent of that observed in cells treated with antioxidants, whose utility in preventing axonal degeneration secondary to mitochondrial inhibition has been suggested by others (Sherer et al., 2003, 2007; Testa et al., 2005).”

“…axonal degeneration resulting from damage caused by mechanical, genetic, or chemical injury (Gillingwater and Ribchester, 2001; Wang et al., 2001a,b; Ferri et al., 2003; Samsam et al., 2003; Araki et al., 2004; Gillingwater et al., 2004; Mi et al., 2005; Sasaki et al., 2006; Zhai et al., 2006).”

“These changes are followed by calpain activation and eventual axonal protein degradation (Coleman, 2005).”

“For example, complex I inhibition and oxidative damage to mitochondrial proteins have been observed in brains of PD patients, changes that can be replicated by treatment of isolated mitochondria with rotenone (Keeney et al., 2006).”

“…of PD (Sherer et al., 2002a); in particular, there is a strong association between PD and exposure to pesticides, including many that inhibit mitochondrial complex I (Semchuk et al., 1992; Gorell et al., 1998, 2004; Priyadarshi et al., 2000, 2001; Ascherio et al., 2006; Brown et al., 2006).”

“44 Additionally, immunofluorescent staining with the protein gene product 9.5 (PGP9.”

“Mitochondrial Reactive Oxygen Species Is Required Following Axotomy for Late-Stage Ca2+ Flux in Distal Axons Because TRPV1 can be directly regulated by redox state and reactive oxygen species (ROS) have been implicated in postaxotomy events (Press and Milbrandt, 2008; Welin et al., 2009; O’Donnell et al., 2013; Wakats…”

“Morphometric analysis of neurite degeneration was performed as described (Press and Milbrandt, 2008), with modifications.”

“NMNAT3 expression in dorsal root ganglia neurones also decreased axonal reactive oxygen species levels and protected against the toxicity of both rotenone and vincristine (23), and NMNAT3 was also able to protect axons of retinal ganglion RGC-5 cells (60).”

“cytNmnat1 mediated axon protection is also independent of NAD and ATP levels (Sasaki et al., 2009; Press and Milbrandt, 2008).”

“However, they do not consume NADH and for conversion to NADPH, which is a cofactor of ROS-scavenging enzymes (Mazzio and Soliman, 2003; Press and Milbrandt, 2008).”

“This, however is not accompanied by neuronal ATP preservation (Press and Milbrandt 2008).”

“and indeed activation of Wallerian degeneration by vincristine does cause an increase in ROS [58].”

“Nmnat1 (or Nmnat3) overexpression alone is sufficient to slow axonal degeneration and this protection is dependent on Nmnat enzymatic activity (Araki et al. 2004; Wang et al. 2005; Sasaki et al. 2006; Press and Milbrandt 2008).”

“This oxidative stress exacerbates inflammation and contributes to axonal damage and degeneration (48).”

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“Morphometric analysis of neurite degeneration was performed as described (Press and Milbrandt, 2008) with modifications.”

“…proteins are essential for neuronal maintenance and protection (Ali et al., 2012; Brazill et al., 2017; Fang et al., 2012; Kitaoka et al., 2013; Press and Milbrandt, 2008; Rossi et al., 2018; Sasaki and Milbrandt, 2010; Sasaki et al., 2009; Wen et al., 2011; Yan et al., 2010; Zhai et al.,…”

“In addition to taxol, we also used the vinca alkaloid derivative vincristine to induce axon degeneration (Wang et al. 2001; Press and Milbrandt 2008; Barrientos et al. 2011; Park et al. 2013; Gerdts et al. 2013).”

“In addition, cells undergo oxidative stress during the initial and developmental stages of MS. Mitochondria are the main source of cellular reactive oxygen species (Kutzelnigg et al., 2005; Press and Milbrandt, 2008).”

“…indirectly due to downstream neuroprotective effects of Wld S pathway activation, such as enhanced mitochondrial calcium buffering, 73 or reduced oxidative stress 74 negating tau-mediated dysregulation in intracellular calcium and/or tau-mediated mitochondrial dysfunction 70,75 or oxidative stress.”

“The concentrations of inhibitors were determined from previous studies (Press and Milbrandt, 2008; Miranda-Goncalves et al., 2013; Tsuyama et al., 2013; Patterson et al., 2014; Anamitra Ghosh, 2016; Ichihara et al., 2017; Babetto et al., 2020).”

“The axon protection conferred by NMNAT1 seems to be closely related to mitochondria, which is a critical organelle for the maintenance of redox state (59, 60).”

“Alternatively, protection may be conferred 399 indirectly due to downstream neuroprotective effects of WldS pathway activation, such as 400 enhanced mitochondrial calcium buffering (66), or reduced oxidative stress (67) negating tau401 mediated dysregulation in intracellular calcium and/or tau-mediated mitochondrial d…”

“We observed axonal degeneration and microtubules bundles disarrangement prior to cellular death, which is in good agreement with previous oxidative stress (OS) studies (Press and Milbrandt, 2008; Fang et al. , 2012; Barsukova et al. , 2012; Datar et al. , 2019).”

“Neurons are particularly susceptible to this damage and increased ROS has been shown to induce Wallerian degeneration in axons (Press and Milbrandt, 2008).”

“These discrepancies were eventually rectified when groups looked at the effect of other Nmnat1 homologs on Wallerian degeneration.”

“Although we could confirm our cell body results, we could not quantitate ROS changes in DA axons with these reagents (data not shown).”