Overexpression of UBQLN1 reduces neuropathology in the P497S UBQLN2 mouse model of ALS/FTD

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.

Serpin neuropathology in the P497S UBQLN2 mouse model of ALS/FTD

“…The P497S Tg line expresses human UBQLN2 under control of the neuron-specific Thy1.2 promoter, whereas the WT356 line expresses an equivalent amount of WT UBQLN2 by the same promoter ( 12 ). Behavioral and pathologic studies have shown that the P497S line recapitulates hallmark features of the human disease, while the WT356 line does not ( 12 , 35 ). Examination of the Log 2 ratio of change in protein expression between the genotypes revealed an increase in several members of the serpin protein family ( Table 1 ).…”

“…Because P497S animals develop MN disease, we also examined lumbar SC sections from all three genotypes for alteration in serpin staining ( Figure 3 ). For this comparison, we used tissue from 32-week-old animals because MNs are still present in P497S animals at this age unlike at 52 weeks when most are lost ( 14 , 35 ). The sections were triple stained for UBQLN2, one of the four serpin proteins, and choline acetyltransferase (ChAT), a MN marker ( Figure 3 and Figure S5 ).…”

“…During the backcrossing the P497S line developed a more attenuated phenotype, exhibiting milder disease symptoms. We recently described the behavioral deficits and pathology of this more attenuated phenotype, showing that at 52 weeks of age P497S mutant animals have diminished grip strength, reduced muscle fiber diameter, massive accumulation of UBQLN2 inclusions in the brain and SC, together with significant loss of neurons in both the dentate gyrus of the brain and of MNs in the SC compared to Non-Tg animals (35). Husbandry, genotyping, and euthanasia of animals was as described previously ( 14, K E Y W O R D S amyotrophic lateral sclerosis (ALS), frontotemporal dementia (FTD), protein aggregation, serpin, Ubiquilin-2 (UBQLN2) 35).…”

“…We recently described the behavioral deficits and pathology of this more attenuated phenotype, showing that at 52 weeks of age P497S mutant animals have diminished grip strength, reduced muscle fiber diameter, massive accumulation of UBQLN2 inclusions in the brain and SC, together with significant loss of neurons in both the dentate gyrus of the brain and of MNs in the SC compared to Non-Tg animals (35). Husbandry, genotyping, and euthanasia of animals was as described previously ( 14, K E Y W O R D S amyotrophic lateral sclerosis (ALS), frontotemporal dementia (FTD), protein aggregation, serpin, Ubiquilin-2 (UBQLN2) 35). All animal procedures were approved by University of Maryland Baltimore Animal Care and Use Committees and conducted in full accordance with the NIH Guide for the Care and Use of Laboratory Animals.…”

UBQLN proteins in health and disease with a focus on UBQLN2 in ALS/FTD

“…The UBQLN2 P497S mouse model may therefore be a useful tool for studying the molecular mechanisms that trigger TDP-43 proteinopathy. Interestingly, crossing an overexpressing UBQLN1 mouse line with the UBQLN2 P497S transgenic line can rescue the motor neuron loss, behavioral deficits, aggregation and TDP-43 proteinopathy [67]. However, an important limitation exists in this model, as transgene expression is restricted to neuronal cell types and any non-cell autonomous disease phenomena will be missed.…”