The alteration of serine transporter activity in a cell line model of amyotrophic lateral sclerosis (ALS)

Abstract

The alteration of D-serine levels is associated with the pathogenesis of sporadic ALS and mutant SOD1 (G93A) animal model of ALS. However, the exact mechanism of D-serine transport is not known in ALS. To better understand the distribution of D-serine in ALS, we determined the activity and the expression of serine transporter in a motor neuronal cell line model of ALS (NSC-34/hSOD1(G93A) cells). The uptake of [3H] D-serine was significantly lower in NSC-34/hSOD1(G93A) cells than in control NSC-34 and NSC-34/ hSOD1(wt) cells. In contrast, the uptake of [3H] L-serine, precursor of D-serine, was markedly increased in NSC-34/hSOD1(G93A) cells compared to control NSC-34 and NSC-34/hSOD1(wt) cells. Both [3H] D-serine and [3H] L-serine uptake were saturable in these cells. The estimated Michaelis-Menten constant, Km, for Dserine uptakes was higher in NSC-34/hSOD1(G93A) cells than in NSC-34/hSOD1(wt) cells while the Km for Lserine uptake was 2 fold lower in NSC-34/hSOD1(G93A) cells than in control cells. [3H] D-serine and [3H] Lserine uptakes took place in a Na+-dependent manner, and both uptakes were significantly inhibited by system ASC (alanine-serine-cysteine) substrates. As a result of small interfering RNA experiments, we found that ASCT2 (SLC1A5) and ASCT1 (SLC1A4) are involved in [3H] D-serine and [3H] L-serine uptake in NSC-34/hSOD1(G93A) cells, respectively. The level of SLC1A4 mRNA was significantly increased in NSC-34/ hSOD1(G93A) compared to NSC-34 and NSC-34/hSOD1(wt) cells. In contrast, the level of SLC7A10 mRNA was relatively lower in NSC-34/hSOD1(G93A) cells than the control cells. Together, these data suggest that the pathological alteration of D-and L-serine uptakes in ALS is driven by the affinity change of D-and L-serine uptake system. (C) 2016 Elsevier Inc. All rights reserved.