The “Second Hit” of Repair in a Rabbit Model of Chronic Rotator Cuff Tear

Abstract

The rabbit supraspinatus is a useful translational model for rotator cuff (RC) repair because it recapitulates muscle atrophy and fat accumulation observed in humans after a chronic tear (the “first hit”). However, a timeline of RC tissue response after repair, especially with regard to recent evidence of muscle degeneration and lack of regeneration, is currently unavailable. Thus, the purpose of this study was to characterize the progression of muscle and fat changes over time after the repair of a chronic RC tear in the rabbit model. Two rounds of experiments were conducted in 2017–2018 and 2019–2020 with N = 18 and 16 skeletally mature New Zealand White rabbits, respectively. Animals underwent left supraspinatus tenotomy with repair 8 weeks later. The unoperated right shoulder served as control. The rabbits were sacrificed at 1-, 2-, 4-, and 8-weeks post-repair for histological and biochemical analysis. Atrophy, measured by fiber cross-sectional area and muscle mass, was greatest around 2 weeks after repair. Active muscle degeneration peaked at the same time, involving 8% of slide areas. There was no significant regeneration at any timepoint. Fat accumulation and fibrosis were significantly increased across all time points compared to contralateral. Statement of Clinical Significance: These results demonstrate model reproducibility and a “second hit” phenomenon of repair-induced muscle atrophy and degeneration which partially recovers after a short time, while increased fat and fibrosis persist.

Nicotinamide Phosphoribosyltransferase‐elevated NAD+ biosynthesis prevents muscle disuse atrophy by reversing mitochondrial dysfunction

“…Previous studies have used rabbits to explore the impact of tenotomy on morphometric changes in the rotator cuff muscles. 21 , 33 , 34 , 35 Ward et al 21 , 33 reported that MyHC I fibres accounted for approximately only 10–20% of the composition of normal supraspinatus muscles, and this differs from the results of our study. In these two studies, the authors analysed the Myosin heavy chain (MHC) content using sodium dodecylsulfate–polyacrylamide gel electrophoresis.…”

“…Previous studies have used rabbits to explore the impact of tenotomy on morphometric changes in the rotator cuff muscles 21,33–35 . Ward et al 21,33 reported that MyHC I fibres accounted for approximately only 10–20% of the composition of normal supraspinatus muscles, and this differs from the results of our study.…”

Spatial transcriptomics tools allow for regional exploration of heterogeneous muscle pathology in the pre-clinical rabbit model of rotator cuff tear

“…Lastly, the different expression pattern of the regenerative markers MYH8 and MYL4 [ 34 ] in healthy vs. torn supraspinatus muscle and even within torn muscle is highly interesting because the degeneration of rotator cuff is still considered irreversible in human [ 15 , 38 ] and animal models [ 28 , 39 ], and it is unclear why certain fibers appear to regenerate while others do not. However, the current dataset was intended to evaluate the use of the technology and its nature only allows qualitative analysis.…”

“…To replicate a rotator cuff tear, tenotomy of the supraspinatus was performed in the rabbit model, and tissues were harvested as previously described [ 3 , 28 , 29 ]. All animals were female New Zealand White and skeletally mature (6 months old, 4.35 ± 0.2 kg).…”

“…One of the advantages of the Visium technology is that it combines transcriptomics with standard hematoxylin & eosin (H&E)-based microscopy. H&E is a gold-standard qualitative tool used by clinicians and researchers to assess muscle fiber integrity, cross-sectional area, central nucleation, and to estimate muscle degeneration, fatty infiltration, and fibrosis [ 6 , 7 , 27 , 28 ]. Unfortunately, skeletal muscle is typically not a prioritized tissue for companies to test and establish protocols which involve enzymatic permeabilization times and subsequent RNA quality and capture efficiency assessments.…”