Amyotrophic lateral sclerosis (ALS) is a lethal disease characterized by degeneration of lower and upper motor neurons. Transactive response DNA-binding protein 43 (TDP-43) ubiquitinated inclusions are a hallmark of ALS. In order to understand the pathogenic mechanism caused by TDP-43, we generated transgenic mice using genomic fragments encoding human TDP-43 wild-type or FALS-linked mutants TDP-43G348C and TDP-43A315T and used these mice to study the pathogenic mechanism associated with ALS. These novel TDP-43 transgenic mice develop many age-related pathological and biochemical changes reminiscent of human ALS. We also found that TDP-43 interacts with and colocalizes with p65, a NF-kappaB subunit, in glial and neuronal cells from ALS patients. We report that TDP-43 and NF-kappaB p65 mRNA and protein expression is higher in spinal cords of ALS patients than healthy individuals. TDP-43 acted as a co-activator of p65. Treatment of TDP-43 mice with Withaferin A, p65 inhibitor, reduced ALS symptoms. We propose that TDP-43 deregulation contributes to ALS pathogenesis in part by enhancing NF-kappaB activation, and that NF-kappaB may constitute a therpeutic target for ALS.