Age‐related effect of cell death on fiber morphology and number in tongue muscle

Abstract

Introduction: Multiple pathways may exist for agerelated tongue muscle degeneration. Cell death is one mechanism contributing to muscle atrophy and decreased function. We hypothesized with aging, apoptosis, and apoptotic regulators would be increased, and muscle fiber size and number would be reduced in extrinsic tongue muscles. Methods: Cell death indices, expression of caspase-3 and Bcl-2, and measures of muscle morphology and number were determined in extrinsic tongue muscles of young and old rats. Results: Significant increases in cell death, caspase-3, and Bcl-2 were observed in all extrinsic tongue muscles along with reductions in muscle fiber number in old rats. Discussion: We demonstrated that apoptosis indices increase with age in lingual muscles and that alterations in apoptotic regulators may be associated with age-related degeneration in muscle fiber size and number. These observed apoptotic processes may be detrimental to muscle function, and may contribute to degradation of cranial functions with age.

Cross Talk opposing view: Myonuclei do not undergo apoptosis during skeletal muscle atrophy

“…Supporting this conclusion is the observation that interventions that trigger atrophy are frequently associated with enhanced expression of apoptosis markers within the tissue, including caspase activation, genomic DNA degradation (measured via TUNEL, terminal deoxynucleotidyl transferase dUTP nick end labelling (TUNEL) staining or DNA ladders on agarose gels), poly (ADP‐ribose) polymerase cleavage or mitochondrial endonuclease G (EndoG) release (Alway et al., 2003; Barnes et al., 2015; Dupont‐Versteegden et al., 2006; Guo et al., 2012; Kletzien et al., 2017; McClung et al., 2007; Smith et al., 2000). On its face, these data appear to support the myonuclear domain hypothesis.…”

Tongue and hypoglossal morphology after intralingual cholera toxin B–saporin injection

“…Each image was converted to 8‐bit resolution and thresholded (between 15 and 35) to allow the fibers to be recognized and outlined by the software. To avoid including blood vessels and other structures, analysis was limited to fibers with CSAs between 75 and 2500 μm 2 and a circularity greater than 0.3 39 …”

Making the head: Caspases in life and death

“…In addition apoptosis was associated with atrophy of skeletal muscles during ageing (Sandri and Carraro, 1999;Schwartz, 2018). Increasing rate of apoptosis was identified in ageing of extrinsic tongue muscle and caspase-3 may be involved in this process (Kletzien et al, 2018).…”