Mutations of optineurin in amyotrophic lateral sclerosis

Abstract

About 10% of cases of the motor neuron disease amyotrophic lateral sclerosis (ALS) are familial, but the small number of mutations so far identified account for only around 20–30% of the those cases. A new study of individuals from ALS-carrying families has now identified three different and previously unknown mutations of OPTN, the gene encoding optineurin. OPTN was earlier reported to be the causative gene of rare familial glaucoma. Optineurin's ability to inhibit activation of the regulatory protein NF-κB is lost in the mutant forms, suggesting that NF-κB inhibitors might be useful in ALS treatment. Amyotrophic lateral sclerosis (ALS) is a disorder characterized by the degeneration of motor neurons. About 10% of cases are familial, but the mutations identified in these families account for only 20–30% of such cases. Here a new set of mutations in familial ALS is found — in the gene encoding optineurin. Given the effect of optineurin mutations on the NF-κB protein, it is suggested that inhibiting NF-κB might be useful in treating ALS. Amyotrophic lateral sclerosis (ALS) has its onset in middle age and is a progressive disorder characterized by degeneration of motor neurons of the primary motor cortex, brainstem and spinal cord1. Most cases of ALS are sporadic, but about 10% are familial. Genes known to cause classic familial ALS (FALS) are superoxide dismutase 1 (SOD1)2, ANG encoding angiogenin3, TARDP encoding transactive response (TAR) DNA-binding protein TDP-43 (ref. 4) and fused in sarcoma/translated in liposarcoma (FUS, also known as TLS)5,6. However, these genetic defects occur in only about 20–30% of cases of FALS, and most genes causing FALS are unknown. Here we show that there are mutations in the gene encoding optineurin (OPTN), earlier reported to be a causative gene of primary open-angle glaucoma (POAG)7, in patients with ALS. We found three types of mutation of OPTN: a homozygous deletion of exon 5, a homozygous Q398X nonsense mutation and a heterozygous E478G missense mutation within its ubiquitin-binding domain. Analysis of cell transfection showed that the nonsense and missense mutations of OPTN abolished the inhibition of activation of nuclear factor kappa B (NF-κB), and the E478G mutation revealed a cytoplasmic distribution different from that of the wild type or a POAG mutation. A case with the E478G mutation showed OPTN-immunoreactive cytoplasmic inclusions. Furthermore, TDP-43- or SOD1-positive inclusions of sporadic and SOD1 cases of ALS were also noticeably immunolabelled by anti-OPTN antibodies. Our findings strongly suggest that OPTN is involved in the pathogenesis of ALS. They also indicate that NF-κB inhibitors could be used to treat ALS and that transgenic mice bearing various mutations of OPTN will be relevant in developing new drugs for this disorder.