Increased ROS Level in Spinal Cord of Wobbler Mice due to Nmnat2 Downregulation

Abstract

Amyotrophic lateral sclerosis is a devastating motor neuron disease and to this day not curable. While 5-10% of patients inherit the disease (familiar ALS), up to 95% of patients are diagnosed with the sporadic form (sALS). ALS is characterized by the degeneration of upper motor neurons in the cerebral cortex and of lower motor neurons in the brainstem and spinal cord. The wobbler mouse resembles almost all phenotypical hallmarks of human sALS patients and is therefore an excellent motor neuron disease model. The motor neuron disease of the wobbler mouse develops over a time course of around 40 days and can be divided into three phases: p0, presymptomatic; p20, early clinical; and p40, stable clinical phase. Recent findings suggest an essential implication of the NAD-producing enzyme Nmnat2 in neurodegeneration as well as maintenance of healthy axons. Here, we were able to show a significant downregulation of both gene and protein expression of Nmnat2 in the spinal cord of the wobbler mice at the stable clinical phase. The product of the enzyme NAD is also significantly reduced, and the values of the reactive oxygen species are significantly increased in the spinal cord of the wobbler mouse at p40. Thus, the deregulated expression of Nmnat2 appears to have a great influence on the cellular stress in the spinal cord of wobbler mice.

Caffeine and NAD+ Improve Motor Neural Integrity of Dissociated Wobbler Cells In Vitro

“…As the coenzyme NAD + was found to be significantly downregulated in the spinal cord of wobbler animals [ 18 ], we aimed to investigate the effect of a NAD + boost on the motor neuronal development. The investigations were equally performed with two developmental stages (p20, p40).…”

“…Since the Nmnat2 level was proven to show a significant downregulation in the spinal cord of wobbler mice [ 18 ], we aimed to study the effect of an elevation of the Nmnat2 level on motor neuronal integrity in vitro. Since Ali and coworkers have shown that caffeine is able to increase the Nmnat2 level in cortical neurons in vitro [ 25 ], we used this compound as treatment of our cell culture.…”

“…It is reported that in an event of DNA damage, NAD + is basically upregulated by Nmnat2 and p53 [ 28 ]. Concerning the wobbler disease, a downregulation of the Nmnat2 level in the clinical phase could be demonstrated, while p53 expression was evidently increased [ 18 , 29 ]. Apparently, a potential DNA damage due to increased oxidative stress [ 30 , 31 ] in wobbler motor neurons cannot be addressed in a physiological way, but presumably only by the p53 pathway.…”

“…In addition to these antioxidative properties, caffeine was detected to cause an increase in the Nmnat2 level in neuronal cells [ 25 ]. Thus, the addition of caffeine to our motor neuronal feeding medium appears to be capable of normalizing Nmnat2 levels in wobbler motor neurons in a deficiency situation [ 18 ].…”

“…Since the NAD + level was proved to be reduced in the cervical spinal cord of wobbler mice at p40 due to a significant downregulation of Nmnat2 [ 18 ], we aimed to investigate the impact of a NAD + enhancement such as an increase in the Nmnat2 expression in motor neuronal cells of wobbler mice on their neurite lengths representative for neuronal health [ 38 ].…”