Abstract|Motor Neuron Disease 1| Volume 357, SUPPLEMENT 1, e48, October 15, 2015

Expression and subcellular localization of FUS protein in fibroblasts of preclinical FUS P525L mutation carriers and patients with sporadic ALS

      Background. Symptom onset in Amyotrophic Lateral Sclerosis (ALS) occurs when over 70% of motor neurons are lost. This suggests an extended preclinical phase, in which no cognitive, electrophysiological or neuroimaging changes are detectable (Eisen A et al., 2014). Furthermore, the availability of genetic testing allows identification of mutation carriers, which might help to understand the molecular changes preceding the clinical onset.
      Objective. To study the expression of FUS protein in skin fibroblasts from preclinical carriers of FUS P525L mutation, a healthy control and patients with sporadic ALS (sALS).
      Patients and methods. Skin fibroblasts from two healthy sisters carrying a FUS P525L mutation and two patients with sALS were cultured. As a control, fibroblasts were taken from a healthy man with no known ALS-related mutations. Western blot and immunocytochemistry were performed to study the expression and subcellular localization of FUS protein in fibroblasts from mutation carriers, control and sALS patients.
      Results. In sALS, FUS protein showed an almost exclusive nuclear localization, where it also forms aggregates. FUS expression was mostly nuclear in control fibroblasts, with a relatively weak cytoplasmic expression. In the two FUS P525L mutation carriers, a high proportion of cells showed a prominent protein localization in both nucleus and cytoplasm, or in the cytoplasm alone.
      Conclusions. FUS protein is differentially localized in fibroblasts from P525L carriers with respect to healthy control and sALS. In the mutation carriers, FUS is often mislocalized in the cytoplasm. This represents the first evidence of specific molecular changes occurring in preclinical ALS.