Ageing and muscular dystrophy differentially affect murine pharyngeal muscles in a region‐dependent manner

Abstract

Key pointsr Millions of elderly individuals have dysphagia, a debilitating and life-threatening condition in which the ability to swallow is impaired.r Several muscles surround the three regions of the pharynx, which are essential for proper swallowing, yet the effects of ageing and disease on these muscles are not well understood.r We demonstrate that the fibre size of murine pharyngeal muscles is differentially affected by ageing and muscular dystrophy depending on their location within the pharynx.r Using a mouse model of an age-associated dysphagic disease (oculopharyngeal muscular dystrophy), we show that overexpression of wild-type polyadenylate binding nuclear protein 1 in muscle tissue prevents age-related dysphagia and age-related muscle atrophy of laryngopharyngeal muscles.r These results demonstrate that mice are an excellent model for studying mechanisms of ageing and disease on pharyngeal muscle physiology, and such studies could lead to new therapies for individuals with dysphagia.Abstract The inability to swallow, or dysphagia, is a debilitating and life-threatening condition that arises with ageing or disease. Dysphagia results from neurological or muscular impairment of one or more pharyngeal muscles, which function together to ensure proper swallowing and prevent the aspiration of food or liquid into the lungs. Little is known about the effects of age or disease on pharyngeal muscles as a group. Here we show ageing affected pharyngeal muscle growth and atrophy in wild-type mice depending on the particular muscle analysed. Furthermore, wild-type mice also developed dysphagia with ageing. Additionally, we studied pharyngeal muscles in a mouse model for oculopharyngeal muscular dystrophy, a dysphagic disease caused by a polyalanine expansion in the RNA binding protein, PABPN1. We examined pharyngeal muscles of mice overexpressing either wild-type A10 or mutant A17 PABPN1. Overexpression of mutant A17 PABPN1 differentially affected growth of the palatopharyngeus muscle dependent on its location within the pharynx. Interestingly, overexpression of wild-type A10 PABPN1 was protective against age-related muscle atrophy in the laryngopharynx and prevented the development of age-related dysphagia. These results demonstrate that pharyngeal muscles are differentially affected by both ageing and muscular dystrophy in a region-dependent manner. These studies lay important groundwork for understanding the molecular and cellular mechanisms that regulate pharyngeal muscle growth and atrophy, which may lead to novel therapies for individuals with dysphagia. Abbreviations A10-WT, wild-type A10.1 PABPN1 overexpression transgenic mouse; A17-MUT, mutant A17.1 PABPN1 overexpression transgenic mouse; FVB, Friend leukaemia virus B; H&E, haematoxylin and eosin; MHC, myosin heavy chains; OPMD, oculopharyngeal muscular dystrophy; PABPN1, polyadenylate binding nuclear protein 1; type I, slow twitch oxidative myofibre; type II, fast twitch glycolytic myofibre; WT, wild-type.

Pharyngeal Satellite Cells Undergo Myogenesis Under Basal Conditions and Are Required for Pharyngeal Muscle Maintenance

“…Each region and their associated muscles vary in both location and function. We recently reported that muscles within the nasal, oral, and laryngeal regions of the pharynx are differentially affected by aging and disease . Therefore, all histologic studies were analyzed based on pharyngeal localization.…”

“… Pharyngeal muscles contain a larger number of activated satellite cells than hindlimb muscle. (A): Schematic representation of murine pharyngeal regions shows NP, OP, and LP (modified from Randolph et al ). (B): Hindlimb (tibialis anterior) and pharyngeal muscles were collected at 9 weeks of age from Myf5‐nlacZ mice, sectioned, and incubated with X‐gal to identify β‐gal + nuclei (blue).…”

“…CO 2 asphyxiation was used to euthanize mice immediately before tissue collection. Pharyngeal tissue dissection was performed as described previously . Histologic samples included pharyngeal tissue extending from the soft palate caudally to the cranial aspects of the trachea and esophagus.…”

“…They are non‐somitic in origin, arising from the cranial mesoderm of the third and fourth pharyngeal arches in vertebrates . These muscles surround the nasal, oral, and laryngeal pharynxes and include the palatopharyngeus, stylopharyngeus, salpingopharyngeus, superior and middle pharyngeal constrictors, cricopharyngeus, and thyropharyngeus muscles . One type of muscular dystrophy in which pharyngeal muscles are pathologically affected is oculopharyngeal muscular dystrophy (OPMD), a late onset autosomal dominant disease caused by a polyalanine expansion in the N‐terminal domain of the ubiquitously expressed polyadenylate‐binding protein nuclear 1 (PABPN1) protein .…”

Proteomic analysis reveals that wildtype and alanine-expanded nuclear poly(A)-binding protein exhibit differential interactions in skeletal muscle

“…Levels of PABPN1 protein are very low in skeletal muscle (15), making biochemical studies of PABPN1 protein interac-tions in this disease-relevant tissue challenging (29). Although several mouse models exist that express PABPN1, they either express native levels of alanine-expanded PABPN1 (33) or do not equally overexpress WT and alanine-expanded PABPN1 (34,35). Thus, we used electroporation into skeletal muscle to allow direct comparison of the proteins that interact with WT PABPN1 and alanine-expanded PABPN1 in skeletal muscle.…”