AUTHOR=Tanaka Miyuu , Fujikawa Ryoko , Sekiguchi Takahiro , Hernandez Jason , Johnson Oleta T. , Tanaka Daisuke , Kumafuji Kenta , Serikawa Tadao , Hoang Trung Hieu , Hattori Kosuke , Mashimo Tomoji , Kuwamura Mitsuru , Gestwicki Jason E. , Kuramoto Takashi 

TITLE=A missense mutation in the Hspa8 gene encoding heat shock cognate protein 70 causes neuroaxonal dystrophy in rats

JOURNAL=Frontiers in Neuroscience

VOLUME=18

YEAR=2024

URL=https://www.frontiersin.org/journals/neuroscience/articles/10.3389/fnins.2024.1263724

DOI=10.3389/fnins.2024.1263724

ISSN=1662-453X

ABSTRACT=<p>Neuroaxonal dystrophy (NAD) is a neurodegenerative disease characterized by spheroid (swollen axon) formation in the nervous system. In the present study, we focused on a newly established autosomal recessive mutant strain of F344-<italic>kk</italic>/<italic>kk</italic> rats with hind limb gait abnormalities and ataxia from a young age. Histopathologically, a number of axonal spheroids were observed throughout the central nervous system, including the spinal cord (mainly in the dorsal cord), brain stem, and cerebellum in F344-<italic>kk</italic>/<italic>kk</italic> rats. Transmission electron microscopic observation of the spinal cord revealed accumulation of electron-dense bodies, degenerated abnormal mitochondria, as well as membranous or tubular structures in the axonal spheroids. Based on these neuropathological findings, F344-<italic>kk</italic>/<italic>kk</italic> rats were diagnosed with NAD. By a positional cloning approach, we identified a missense mutation (V95E) in the <italic>Hspa8</italic> (heat shock protein family A (Hsp70) member 8) gene located on chromosome 8 of the F344-<italic>kk</italic>/<italic>kk</italic> rat genome. Furthermore, we developed the <italic>Hspa8</italic> knock-in (KI) rats with the V95E mutation using the CRISPR-Cas system. Homozygous <italic>Hspa8</italic>-KI rats exhibited ataxia and axonal spheroids similar to those of F344-<italic>kk</italic>/<italic>kk</italic> rats. The V95E mutant HSC70 protein exhibited the significant but modest decrease in the maximum hydrolysis rate of ATPase when stimulated by co-chaperons DnaJB4 and BAG1 <italic>in vitro</italic>, which suggests the functional deficit in the V95E HSC70. Together, our findings provide the first evidence that the genetic alteration of the <italic>Hspa8</italic> gene caused NAD in mammals.</p>