-実験動物開発室-

Pathomechanistic model mice of sporadic ALS:
Conditional ADAR2 knockout mice AR2

B6.Cg-Adarb1<tm1.1Skwa> Tg(SLC18A3-cre)KMisa (RBRC09428)

Courtesy of Shin Kwak, M.D., Ph.D.

(a) An AR2 mouse at 12 months of age (left panel) exhibits abnormal posture of the hind-limbs and the tail, as compared with normal posture of a control littermate (right panel). (b) Temporal profile of Cre expression in the motor neurons is indicated as the proportion of Cre-expressing and ADAR2-lacking motor neurons in the spinal anterior horns of the AR2 mice. Cre expression reached the maximum level (~50% of motor neurons) by postnatal week 5. AHCs: anterior horn cells. (c) The ADAR2^flox gene, transcripts of the Cre gene and the ADAR2^flox alleles before and after Cre-recombination in the laser-captured motor neurons were analyzed for each group by PCR. In addition, proportion of Q/R site-edited GluA2 in all the GluA2 expressed in motor neurons were calculated in ADAR2(−), ADAR2(+) motor neurons of AR2 mice and motor neurons of the littermate control mice (ADAR2^flox/flox mice and VAChT-Cre.Fast mice). ADAR2 (−) motor neurons expressed only unedited GluR2 (GluA2) mRNA, harboring the truncated ADAR2^floxgene and Cre transcripts, whereas ADAR2 (+) motor neurons expressed only edited GluR2 mRNA, carrying the full-length ADAR2^flox gene and did not express Cre. Motor neurons of the littermate control mice expressed full-length ADAR2 and only edited GluA2 mRNA.

Amyotrophic lateral sclerosis (ALS) is a progressive adult-onset motor neuron disease. Patients with ALS develop progressive muscle weakness resulting from both upper and lower motor neurons and ultimately lose the ability to breathe without mechanical support within a few years of onset. Although little is known about pathogenesis of sporadic ALS, which accounts for more than 90% of ALS cases, recent studies demonstrated that failure of adenosine-inosine (A-I) conversion at the glutamine/arginine (Q/R) site of GluA2, a subunit of α-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA) receptors, resulting from downregulation of an RNA-editing enzyme adenosine deaminase acting on RNA 2 (ADAR2) plays pivotal role in the ALS pathogenesis [1, 2]. AR2 mice mimic this molecular abnormality and exhibit ALS phenotype via mechanism mediated by Ca²⁺-permeable AMPA receptors that have Q/R site-unedited GluA2 in their subunit assembly [3]. In addition, TDP-43 pathology, a hallmark of ALS, is observed in the motor neurons devoid of ADAR2 immunoreactivity in the patients with ALS and ADAR2-lacking motor neurons of AR2 mice, in a calcium-dependent protease calpain-dependent manner [4, 5]. As restoration of ADAR2 activity by gene therapy using adeno-associated virus (AAV) rescues ALS phenotype and TDP-43 pathology in AR2 mice [6], the AR2 mice will be useful in ALS research aiming at both elucidating etiology and developing therapy.