In healthy striated muscle, damaged mitochondria are degraded through mitophagy, maintaining the function of striated muscle stem cells and muscle tissue homeostasis [1]. While autophagy activity decreases with age leading to muscle mass reduction [2], detailed studies on mitochondrial morphology in the rhabdosphincter (RS) of elderly individuals are lacking. This study aimed to detect mitochondrial morphology and mitophagy activity in the RS. To our knowledge, this is the first study to comprehensively investigate mitochondrial morphology and mitophagy activity in the RS of elderly individuals.

To investigate the mitochondrial abnormalities occurring in the RS, morphological observations of mitochondria were performed using transmission electron microscopy (TEM). RS and rectus abdominis muscle (RA) samples as controls were collected from patients undergoing radical cystectomy at our department (n = 8). Morphological observations of muscle tissue and mitochondrial area, perimeter, and luminance measurements were performed using TEM. Next, the expression of mitophagy-related factors was analyzed by reverse transcription-polymerase chain reaction (RT-PCR). The Welch's t-test was used for statistical analysis, and p < 0.05 was considered statistically significant. This study conformed to the standards set by the most recent version of the Declaration of Helsinki (except for registration in a database) and was approved by our Institutional Review Board. All study participants provided oral and written informed consent.

HE staining revealed that the RS tissue had fewer muscle fibers and more interstitial tissue than the RA tissue. TEM images showed increased gaps in RS muscle bundles, decreased mitochondrial numbers, and mitochondrial vacuolation and swelling compared to the RA tissue. Furthermore, the quantitative evaluation of mitochondrial morphology revealed significantly larger mean area (0.21 μm² vs 0.063 μm², p < 0.01), longer perimeter (1.83 μm vs 0.94 μm, p < 0.01), and higher luminance (156.6 vs 90.2, p < 0.01) of mitochondria in RS tissue compared to RA tissue (Figure 1). Moreover, RT-PCR analysis revealed that, compared to RA, the expression of mitophagy-related factors was upregulated in RS: microtubule-associated protein 1 light chain 3A (LC3A) by 16.7-fold, microtubule-associated protein 1 light chain 3B (LC3B) by 20.5-fold, and Beclin 1 by 2.6-fold. The increases in LC3A and LC3B expression were statistically significant (LC3A: p = 0.033; LC3B: p = 0.019; Beclin 1: p = 0.18) (Figure 2).

The findings indicate significant mitochondrial morphological abnormalities and enhanced mitophagy in the RS tissue compared to the RA tissue. These changes suggest increased mitochondrial damage and turnover in the RS, potentially contributing to functional decline.

The observed mitochondrial abnormalities and enhanced mitophagy in the RS suggest that dysregulation of mitochondrial quality control may play a role in the development of urinary incontinence. Regulation of mitophagy may represent a novel therapeutic approach for this condition.

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Romanello, V., & Sandri, M. (2021). The connection between the dynamic remodeling of the mitochondrial network and the regulation of muscle mass. Cellular and molecular life sciences. Cellular and Molecular Life Sciences, 78(4), 1305–1328. https://doi.org/10.1007/s00018-020-03662-0