Poly(ADP-Ribose) Polymerases-Inhibitor Talazoparib Inhibits Muscle Atrophy and Fatty Infiltration in a Tendon Release Infraspinatus Sheep Model: A Pilot Study

Abstract

Structural muscle changes, including muscle atrophy and fatty infiltration, follow rotator cuff tendon tear and are associated with a high repair failure rate. Despite extensive research efforts, no pharmacological therapy is available to successfully prevent both muscle atrophy and fatty infiltration after tenotomy of tendomuscular unit without surgical repair. Poly(ADP-ribose) polymerases (PARPs) are identified as a key transcription factors involved in the maintenance of cellular homeostasis. PARP inhibitors have been shown to influence muscle degeneration, including mitochondrial hemostasis, oxidative stress, inflammation and metabolic activity, and reduced degenerative changes in a knockout mouse model. Tenotomized infraspinatus were assessed for muscle degeneration for 16 weeks using a Swiss Alpine sheep model (n = 6). All sheep received daily oral administration of 0.5 mg Talazoparib. Due to animal ethics, the treatment group was compared with three different controls from prior studies of our institution. To mitigate potential batch heterogeneity, PARP-I was evaluated in comparison with three distinct control groups (n = 6 per control group) using the same protocol without treatment. The control sheep were treated with an identical study protocol without Talazoparib treatment. Muscle atrophy and fatty infiltration were evaluated at 0, 6 and 16 weeks post-tenotomy using DIXON-MRI. The controls and PARP-I showed a significant (control p < 0.001, PARP-I p = 0.01) decrease in muscle volume after 6 weeks. However, significantly less (p = 0.01) atrophy was observed in PARP-I after 6 weeks (control 1: 76.6 ± 8.7%; control 2: 80.3 ± 9.3%, control 3: 73.8 ± 6.7% vs. PARP-I: 90.8 ± 5.1% of the original volume) and 16 weeks (control 1: 75.7 ± 9.9; control 2: 74.2 ± 5.6%; control 3: 75.3 ± 7.4% vs. PARP-I 93.3 ± 10.6% of the original volume). All experimental groups exhibited a statistically significant (p < 0.001) augmentation in fatty infiltration following a 16-week period when compared to the initial timepoint. However, the PARP-I showed significantly less fatty infiltration (p < 0.003) compared to all controls (control 1: 55.6 ± 6.7%, control 2: 53.4 ± 9.4%, control 3: 52.0 ± 12.8% vs. PARP-I: 33.5 ± 8.4%). Finally, a significantly (p < 0.04) higher proportion and size of fast myosin heavy chain-II fiber type was observed in the treatment group. This study shows that PARP-inhibition with Talazoparib inhibits the progression of both muscle atrophy and fatty infiltration over 16 weeks in retracted sheep musculotendinous units.

Keywords: PARP inhibition; experimental sheep model; fatty infiltration; muscle atrophy; rotator cuff rupture.

Figure 1

Muscle volume, normalized to the initial volume (T0) of the right (tenotomy A,C) and left (contralateral B,D) infraspinatus muscles in sheep, illustrating the difference between groups (C,D) and the effect of time (A,B). The treatment group, denoted as PARP-I, received the PARP inhibitor Talazoparib. An asterisk (*) indicates a statistically significant difference with a p-value of <0.05. The timepoint 6 weeks post-tenotomy is represented by T6, while T16 denotes the timepoint 16 weeks post-tenotomy.

Figure 2

MRI-Dixon fat content (%) of the right (tenotomy A,C) and left (contralateral B,D) infraspinatus muscles in sheep, illustrating the difference between groups (C,D) and the effect of time (A,B). The treatment group, denoted as PARP-I, received the PARP inhibitor Talazoparib. An asterisk (*) indicates a statistically significant difference with a p-value of <0.05. The timepoint 6 weeks post-tenotomy is represented by T6, while T16 denotes the timepoint 16 weeks post-tenotomy.

Figure 3

Musculotendinous retraction (A), muscle fiber pennation angle (B) and muscle fiber length (C) of tenotomized sheep infraspinatus muscles over time. The treatment group, denoted as PARP-I, received the PARP inhibitor Talazoparib. The timepoint 6 weeks post-tenotomy is represented by T6, while T16 denotes the timepoint 16 weeks post-tenotomy.

Figure 4

Histological analysis of supraspinatus muscle biopsies 16 weeks post-tenotomy: distribution of myosin heavy-chain (MHC) muscle fiber types and histological fat content in percentages (A), with the mean cross-sectional area of fibers presented in µm² (B). Panel (C) showcases representative sections stained with double immunofluorescence for MHC typing (MHC-type) alongside Oil Red O for lipid content (fat content). S denotes slow muscle fibers, F indicates fast muscle fibers and H marks hybrid fast/slow fibers. Fat is visualized in red by Oil Red O staining. Scale bars are set at 100 µm for MHC immunofluorescence and 500 µm for Oil Red O lipid staining. The treatment group, denoted as PARP-I, received the PARP inhibitor Talazoparib. The control group displays the histological characteristics of the infraspinatus muscle 16 weeks after tenotomy without any treatment. An asterisk (*) indicates a statistically significant difference with a p-value of <0.05.