# Characterization of Skeletal Muscle Regeneration Revealed a Novel Growth Network Induced by Molecular Acupuncture-like Transfection

## TL;DR

A new muscle growth network was discovered using a method similar to acupuncture, which amplifies growth signals in regenerating muscle tissue.

## Contribution

A novel signaling network for muscle regeneration was identified, initiated by transfection of a few muscle fibers.

## Key findings

- Transfection of a few muscle fibers triggered a network that amplified growth signals in the entire regenerating muscle.
- SERCA1b and Ras signaling were shown to regulate muscle fiber growth and differentiation during regeneration.
- Growth stimulation was dependent on calcineurin and IL4, and ceased once muscle fibers reached full size.

## Abstract

The low efficiency of in vivo transfection of a few fibres revealed a novel tissue network that temporally amplified growth stimulation in the entire regenerating rat soleus muscle. This acupuncture-like effect was demonstrated when the fibres began to grow after complete fibre degradation, synchronous inflammation, myoblast and myotube formation. Neonatal sarcoplasmic/endoplasmic reticulum ATPase (SERCA1b) was first detected in this system. The neonatal, fast and slow SERCA isoforms displayed consequent changes with innervation and differentiation, recapitulating events in muscle development. In vivo transfection of myotubes with plasmids expressing dominant negative Ras or a calcineurin inhibitor peptide (Cain/cabin) proved that expression of the slow myosin heavy chain and the slow muscle type SERCA2a are differentially regulated. In vivo transfection of a few nuclei of myotubes with dnRas or SERCA1b shRNA stimulated fibre size growth in the whole regenerating muscle but only until the full size had been reached. Growth stimulation by Ras and SERCA1b antisense was abolished by co-transfection of Cain or with perimuscular injection of IL4 antibody. This revealed a novel signalling network resembling scale-free networks which, starting from transfected fibre myonuclei as “hubs”, can amplify growth stimulation uniformly in the entire regenerating muscle.