Quantitative study of the effects of long-term denervation on the extensor digitorum longus muscle of the rat

Abstract

Background In order to understand the cellular basis underlying the progressively poorer restorative capacity of long‐term denervated muscle, we determined the effects of long‐term denervation on the muscle fibers and satellite cell population of the rat extensor digitorum longus (EDL) muscle. Methods In 36 male rats, the right hind legs were denervated, and EDL muscles were removed 2, 4, 7, 12, and 18 months later. Muscles were either fixed for electron microscopic analysis or were dissociated into individual muscle fibers for direct fiber counting or for confocal microscopic analysis. Results The percentage of satellite cells rose from the 2.8% control value to 9.1% at 2 months of denervation; thereafter the percentage decreased to 1.1% at 18 months of denervation. The number of myonuclei per muscle fiber steadily declined from 410 in 4 month control muscle to 158 in 7 month denervated muscle. Up to 7 months of denervation, the total number of muscle fibers per muscle remained relatively constant at somewhat over 5,000. The calculated total satellite cell population in 4 month denervated EDL muscle was the same as that of controls at 65,000, but by 7 months of denervation it had declined to 21,000. With increasing time of denervation, the number of cross‐sectional profiles of muscle fibers not containing nuclei rose from 14% in control muscle to 49% in 12 month denervated muscle. This was correlated with a pronounced regular clumping of the nuclei, with pronounced nonnucleated segments between nuclear clumps. Conclusions Increasing times of denervation are accompanied by a pronounced decline in the number of myonuclei per muscle fiber and an initial rise and subsequent fall in satellite cell number. These changes are correlated with a decreasing restorative ability of these muscles over the same periods of denervation. Further work on the proliferative capacity of the remaining satellite cells is necessary before firm quantitative conclusions can be made. Anat. Rec. 248:346‐354 1997. © 1997 Wiley‐Liss, Inc.

Differentiation of activated satellite cells in denervated muscle following single fusions in situ and in cell culture

“…Counting of satellite cells in denervated muscle using electron microscopy demonstrated a 2-to 3-fold increase in their number during the first weeks following denervation (Vigue et al 1997), which provides the direct evidence of satellite cell proliferation. Our earlier studies have shown that in the rat extensor digitorum longus muscle, the number of satellite cells related to the total number of nuclei had progressively decreased from 9.1±0.1% to 0.51±0.03% in 2 month denervated and 25 month denervated muscle, respectively (Vigue et al 1997;Dedkov et al 2001). A plausible explanation of this fact is that the precursor cells are involved in myogenesis, and their pool is gradually exhausting during the course of post-denervation muscle atrophy.…”

“…It remains unclear why muscle tissue atrophies despite the presence of a large reserve of myogenic cells. Paradoxically, there is evidence that in denervated muscle the number of satellite cells may double or triple during the first few weeks following denervation (for discussion, see Vigue et al 1997). Thus, understanding the behavior and properties of myoblasts in atrophying muscle is of great biological and clinical importance.…”

mRNA expression of fibroblast growth factors and hepatocyte growth factor in rat plantaris muscle following denervation and compensatory overload

“…Proliferating cell nuclear antigen-positive and myogenin-positive cells, the proliferative and differentiative compartments of cells, in an isolated cell culture from denervated muscle are decreased after 1 week or more, and denervation for 1 week or longer hinders recruitment into the mitotic cycle [17]. Prolonged denervation decreases the number of myonuclei and satellite cells [6,28,33,42]. These observations suggest that muscle atrophy following denervation may be related to inactivation of myonuclei and satellite cells.…”

“…Short-term denervation induces satellite cells to enter the mitotic cycle [20,21,23], whereas long-term denervation decreases the number of both myonuclei and satellite cells [6,28,33,42]. Satellite cells isolated from denervated muscle for 1 week or longer are resistant to recruitment into the mitotic cycle [17].…”

Abortive myogenesis in denervated skeletal muscle: differentiative properties of satellite cells, their migration, and block of terminal differentiation

“…The available data mainly concern muscles denervated for less than 3-6 weeks. Paradoxically, the number of myogenic satellite cells significantly increases during the first several weeks following denervation (for discussion, see Lu et al 1997 andViguie et al 1997). Activation of DNA synthesis in satellite cells and an increase in their number at early stages following denervation have been reported in mammalian denervated muscles by several groups (for discussion, see Gosselin et al 1994, Murray and Robbins 1982, Ontell 1974, Schultz 1978and Snow 1983.…”