Overexpression of UBQLN1 reduces neuropathology in the P497S UBQLN2 mouse model of ALS/FTD
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RESEARCH
Overexpression of UBQLN1 reduces neuropathology in the P497S UBQLN2 mouse model of ALS/FTD Shaoteng Wang, Micaela Tatman and Mervyn J. Monteiro*
Abstract Missense mutations in UBQLN2 cause X-linked dominant inheritance of amyotrophic lateral sclerosis with frontotemporal dementia (ALS/FTD). UBQLN2 belongs to a family of four highly homologous proteins expressed in humans that play diverse roles in maintaining proteostasis, but whether one isoform can substitute for another is not known. Here, we tested whether overexpression of UBQLN1 can alleviate disease in the P497S UBQLN2 mouse model of ALS/ FTD by crossing transgenic (Tg) mouse lines expressing the two proteins and characterizing the resulting genotypes using a battery of pathologic and behavioral tests. The pathologic findings revealed UBQLN1 overexpression dramatically reduced the burden of UBQLN2 inclusions, neuronal loss and disturbances in proteostasis in double Tg mice compared to single P497S Tg mice. The beneficial effects of UBQLN1 overexpression were primarily confirmed by behavioral improvements seen in rotarod performance and grip strength in male, but not female mice. Paradoxically, although UBQLN1 overexpression reduced pathologic signatures of disease in P497S Tg mice, female mice had larger percentage of body weight loss than males, and this correlated with a corresponding lack of behavioral improvements in the females. These findings lead us to speculate that methods to upregulate UBQLN1 expression may reduce pathogenicity caused by UBQLN2 mutations, but may also lead to gender-specific outcomes that will have to be carefully weighed with the therapeutic benefits of UBQLN1 upregulation. Keywords: Amyotrophic lateral sclerosis, UBQLN1, UBQLN2, Motor neuron disease, Proteostasis
Introduction Ubiquilin (UBQLN) proteins function in regulation of proteostasis [15]. The proteins are highly conserved across species [19, 20]. Humans contain four UBQLN protein isoforms, encoded by separate genes that are differentially expressed in the body. UBQLN1 is the most widely expressed isoform, whereas UBQLN2 and UBQLN4 have more restricted expression patterns [4,
*Correspondence: [email protected] Center for Biomedical Engineering and Technology and Department of Anatomy and Neurobiology, University of Maryland School of Medicine, Baltimore, MD, USA
13, 19]. UBQLN3 is only expressed in the testis [3]. The proteins encoded by the four genes are all approximately 600 amino acids long. Of the four isoforms, UBQLN 1, 2 and 4 share the greatest homology (70–83% identity to one other), with UBQLN 3 being least related (~ 35%) (Fig. 1a). Interestingly, UBQLN1 and UBQLN2 are the most closely related isoforms (74 and 83%, respectively) (Fig. 1a). However, it is unclear whether the different UBQLN isoforms have unique or redundant functions. Information published on the knockout (KO) of UBQLN genes in rodents indicates neither UBQLN1 nor 2 is essential for animal survival [17, 36]. The only deficiency noted was increased vulnerabil
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