Reduction in hSOD1 copy number significantly impacts ALS phenotype presentation in G37R (line 29) mice: implications for the assessment of putative therapeutic agents

Abstract

BackgroundIn vivo animal models of familial amyotrophic lateral sclerosis (fALS) are widely used to delineate the potential role that genetic mutations play in the neurodegenerative process. While these models are extensively used for establishing the safety and efficacy of putative therapeutics during pre-clinical development, effective clinical translation of pharmacological interventions has been largely unsuccessful.ResultsIn this report we compare a recent cohort of G37R (line 29) mice generated from mating wild-type females with transgenic males obtained commercially to a previous set of offspring produced with transgenic male breeders from a colony established at a local collaborator’s facility. Commercially derived progeny presented with a tightly clustered genomic signature for the mutant human superoxide dismutase1 transgene (hSOD1) locus, and exhibited a greater than two-fold reduction in the number of transgene copies present in the genome compared to offspring derived locally. Decrease in transgene levels corresponded with delayed ALS progression and a significant increase in overall lifespan (146%).ConclusionsThese results highlight some key challenges inherent to the use of G37R (line 29) animals in pre-clinical studies for the development of ALS therapeutics. Without stringent assessment of mutant SOD1 copy number/protein levels, heterogeneity of transgene levels within cohorts may influence the behavioural and pathological presentation of disease and thus calls to question the validity of any detected therapeutic effects. Nuanced changes in mutant SOD1 copy number that currently remain unreported may undermine research endeavours, delay efforts for clinical translation, and compromise the rigor of animal studies by limiting reproducibility amongst research groups.

Sex-Specific Differences in Motor-Unit Remodeling in a Mouse Model of ALS

“…Importantly, however, these differences depend on the presence of genetic modifiers (Heiman-Patterson et al, 2005). Furthermore, female mice from another SOD1 G37R line (line 29) have reduced survival and tend to have a delayed onset (Zwiegers et al, 2014), which is reminiscent of our present finding in loxSOD1 G37R mice. These results contrast with a recent study on Chinese familial ALS patients carrying SOD1 mutations which identified that women tended to have a slower progression and longer survival after onset (Tang et al, 2019).…”

“…Sex-specific differences have been identified in other SOD1 mouse models and in patients carrying SOD1 mutations, but they did not consistently point toward a faster or more severe disease in one sex (Hayworth and Gonzalez-Lima, 2009;Kim et al, 2012;Zwiegers et al, 2014;Pfohl et al, 2015;Tang et al, 2019). For instance, male SOD1 G93A mice have an earlier onset than female SOD1 G93A mice (Hayworth and Gonzalez-Lima, 2009;Kim et al, 2012;Pfohl et al, 2015).…”

Disparity of outcomes: the limits of modeling amyotrophic lateral sclerosis in murine models and translating results clinically

“…Our recent experience with the G37R model underscores this dilemma in that we had generated a colony of animals from commercial breeders with an uncharacterized drop in copy number. As expected, these presented with a concomitant increase in lifespan and delay in disease progression (83). Transgene level variation can arise due to meiotic recombination.…”

Differential Vulnerability of Oculomotor Versus Hypoglossal Nucleus During ALS: Involvement of PACAP

“…On the other hand, it promoted axonal regeneration process after nerve injury and protected rat motor neurons in culture against glutamate-induced excitotoxicity and iPSC-derived motor neurons from apoptosis. of disease presentation (Zwiegers et al, 2014;Lutz, 2018); secondly, the overexpression of human wild-type SOD1 causes axonopathy in mice, challenging the role of the mutation as the driver of pathology (Joyce et al, 2011).…”

“…Although SOD1 G93A mice is the widely used animal model, reproducing motor defects similar to that observed in ALS-affected patients, there are important caveats to acknowledge. Firstly, the mSOD1 mouse model has a propensity to spontaneously delete copy number which can alter the severity of disease presentation ( Zwiegers et al, 2014 ; Lutz, 2018 ); secondly, the overexpression of human wild-type SOD1 causes axonopathy in mice, challenging the role of the mutation as the driver of pathology ( Joyce et al, 2011 ).…”