Optimizing the Translational Value of Mouse Models of ALS for Dysphagia Therapeutic Discovery

Abstract

The goal of this study was to compare dysphagia phenotypes in low and high copy number (LCN and HCN) transgenic superoxide dismutase 1 (SOD1) mouse models of ALS to accelerate the discovery of novel and effective treatments for dysphagia and early amyotrophic lateral sclerosis (ALS) diagnosis. Clinicopathological features of dysphagia were characterized in individual transgenic mice and age-matched controls utilizing videofluoroscopy in conjunction with postmortem assays of the tongue and hypoglossal nucleus. Quantitative PCR accurately differentiated HCN-SOD1 and LCN-SOD1 mice and nontransgenic controls. All HCN-SOD1 mice developed stereotypical paralysis in both hindlimbs. In contrast, LCN-SOD1 mice displayed wide variability in fore-and hindlimb involvement. Lick rate, swallow rate, inter-swallow interval, and pharyngeal transit time were significantly altered in both HCN-SOD1 and LCN-SOD1 mice compared to controls. Tongue weight, tongue dorsum surface area, total tongue length, and caudal tongue length were significantly reduced only in the LCN-SOD1 mice compared to age-matched controls. LCN-SOD1 mice with lower body weights had smaller/lighter weight tongues, and those with forelimb paralysis and slower lick rates died at a younger age. LCN-SOD1 mice had a 32% loss of hypoglossal neurons, which differed significantly when compared to age-matched control mice. These novel findings for LCN-SOD1 mice are congruent with reported dysphagia and associated tongue atrophy and hypoglossal nucleus pathology in human ALS patients, thus highlighting the translational potential of this mouse model in ALS research.

Intralingual Administration of AAVrh10-miRSOD1 Improves Respiratory But Not Swallowing Function in a Superoxide Dismutase-1 Mouse Model of Amyotrophic Lateral Sclerosis

“…Swallowing function was also assessed every other week (the day after plethysmography) by using a VFSS protocol described in detail elsewhere. 20,30,31 Briefly, the night before testing, mice were water restricted for *14 h to encourage their willingness to drink while in the fluoroscope. A custom-designed, translucent/radiolucent, polycarbonate VFSS test chamber was added to the home cage overnight to allow acclimation.…”

“…We have previously used VFSS to assess a variety of swallowing metrics and have shown that end-stage MT mice have significantly slower lick and swallow rates compared with WT mice. 20,24,25 MT mice also lose weight rapidly as they approach end stage, and it would be logical to hypothesize that this is due, at least in part, to an impaired ability to ingest calories.…”

“…14,15 SOD1 G93A is the most commonly used mouse model of ALS and has been proven to recapitulate many aspects of ALS, including motor neuron loss, axonal degeneration, muscle denervation, limb paralysis, respiratory insufficiency, and orolingual motor deficits including dysphagia. [16][17][18][19][20][21][22][23][24][25] We previously reported that AAVrh10-miR SOD1 (hereafter referred to as miR SOD1 ) prolonged survival by 69 days when injected into neonatal mice 14 and by 22-27 days when administered intravenously to adult mice. 15 Although SOD1 expression was decreased and survival was prolonged, both sets of mice showed evidence of impaired respiratory function (swallowing function was not assessed in these studies).…”

A Mouse Model of Dysphagia After Facial Nerve Injury

“…Here, we investigated the stereotypical oropharyngeal deglutitive behavior of mice before and after MT versus MMB transection, evaluated using our previously validated videofluoroscopic swallow study (VFSS) methodology. 39,40,43,62 Based on our previous work, we expected VFSS outcome measures would be altered in a predictable direction: MT injury would result in slower lick and swallow rates, longer inter-swallow intervals, and greater lick-swallow ratios (i.e., vallecular fill time), collectively indicative of oropharyngeal (i.e., oral and pharyngeal stage) dysphagia; MMB injury would result solely in slower lick rate (i.e., oral stage dysphagia). Although we expected that MT transection would produce a more robust model for translational investigations of dysphagia treatment discovery, we recognize the potential benefits of establishing an MMB injury model: elimination of morbidity associated with impaired eye blink and vibrissae movement and confounding stress-induced responses associated with frequent daily handling for application of ocular lubricant.…”

Recurrent laryngeal nerve transection in mice results in translational upper airway dysfunction

“…Despite these differences, both species use the tongue, jaw, and other oral cavity structures to facilitate the oral (i.e., preparatory or transport stage) and pharyngeal stages of swallowing and are presumed to utilize common neural substrates (Lever, Brooks, et al, ; Sang & Goyal, ). In fact, videofluoroscopic swallow studies have been used to document dysphagia in rodent models of amyotrophic lateral sclerosis (Lever, Braun, et al, ; Osman et al, ) and presbyphagia (Lever, Brooks, et al, ). The affected swallow metrics identified in these studies suggest that the swallowing mechanism is sufficiently similar between the two species and can be used in future investigations examining the neurologic pathways responsible for swallow function.…”