Pelvic floor muscle (PFM) injury during childbirth is a key risk factor for pelvic floor disorders that affect millions of women worldwide. Muscle stem cells (MuSCs), supported by the fibro-adipogenic progenitors (FAPs) and immune cells, are indispensable for the regeneration of injured appendicular skeletal muscles. However, almost nothing is known about their role in PFM regeneration following birth injury. To elucidate the role of MuSCs, FAPs, and immune infiltrate in this context, we used radiation to perturb cell function and followed PFM recovery in a validated simulated birth injury (SBI) rat model. Non-irradiated and irradiated rats were euthanized at 3,7,10, and 28 days post-SBI (dpi). Twenty-eight dpi, PFM fiber cross-sectional area (CSA) was significantly lower and the extracellular space occupied by immune infiltrate was larger in irradiated relative to nonirradiated injured animals. Following SBI in non-irradiated animals, MuSCs and FAPs expanded significantly at 7 and 3 dpi, respectively; this expansion did not occur in irradiated animals at the same time points. At 7 and 10 dpi, we observed persistent immune response in PFMs subjected to irradiation compared to non-irradiated injured PFMs. CSA of newly regenerated fibers was also significantly smaller following SBI in irradiated compared to non-irradiated injured PFMs. Our results demonstrate that the loss of function and decreased expansion of MuSCs and FAPs after birth injury lead to impaired PFM recovery. These findings form the basis for further studies focused on the identification of novel therapeutic targets to counteract postpartum PFM dysfunction and the associated pelvic floor disorders.

Muscle stem cells (MuSCs) are involved in homeostatic maintenance of skeletal muscle and play a central role in muscle regeneration in response to injury. Thus, understanding MuSC autonomous properties is of fundamental importance for studies of muscle degenerative diseases and muscle plasticity. Rat, as an animal model, has been widely used in the skeletal muscle field, however rat MuSC isolation through fluorescence-activated cell sorting has never been described. This work validates a protocol for effective MuSC isolation from rat skeletal muscles. Tibialis anterior was harvested from female rats and digested for isolation of MuSCs. Three protocols, employing different cell surface markers (CD106, CD56, and CD29), were compared for their ability to isolate a highly enriched MuSC population. Cells isolated using only CD106 as a positive marker showed high expression of Pax7, ability to progress through myogenic lineage while in culture, and complete differentiation in serum-deprived conditions. The protocol was further validated in gastrocnemius, diaphragm, and the individual components of the pelvic floor muscle complex (coccygeus, iliocaudalis, and pubocaudalis), proving to be reproducible. CD106 is an efficient marker for reliable isolation of MuSCs from a variety of rat skeletal muscles.

Muscle stem cells (MuSCs) exhibit distinct behavior during successive phases of developmental myogenesis. However, how their transition to adulthood is regulated is poorly understood. Here, we show that fetal MuSCs resist progenitor specification and exhibit altered division dynamics, intrinsic features that are progressively lost postnatally. After transplantation, fetal MuSCs expand more efficiently and contribute to muscle repair. Conversely, niche colonization efficiency increases in adulthood, indicating a balance between muscle growth and stem cell pool repopulation. Gene expression profiling identified several extracellular matrix (ECM) molecules preferentially expressed in fetal MuSCs, including tenascin-C, fibronectin, and collagen VI. Loss-of-function experiments confirmed their essential and stage-specific role in regulating MuSC function. Finally, fetal-derived paracrine factors were able to enhance adult MuSC regenerative potential. Together, these findings demonstrate that MuSCs change the way in which they remodel their microenvironment to direct stem cell behavior and support the unique demands of muscle development or repair.

Most human cancers originate from high-turnover tissues, while low-proliferating tissues, like skeletal muscle, exhibit a lower incidence of tumor development. In Duchenne muscular dystrophy (DMD), which induces increased skeletal muscle regeneration, tumor incidence is increased. Rhabdomyosarcomas (RMSs), a rare and aggressive type of soft tissue sarcoma, can develop in this context, but the impact of DMD severity on RMS development and its cell of origin are poorly understood. Here, we show that RMS latency is affected by DMD severity and that muscle stem cells (MuSCs) can give rise to RMS in dystrophic mice. We report that even before tumor formation, MuSCs exhibit increased self-renewal and an expression signature associated with RMSs. These cells can form tumorspheres in vitro and give rise to RMSs in vivo. Finally, we show that the inflammatory genes Ccl11 and Rgs5 are involved in RMS growth. Together, our results show that DMD severity drives MuSC-mediated RMS development.

Phenolic compounds in fruit provide human health benefits, and they contribute to color, taste, and the preservation of post-harvest fruit quality. Phenolic compounds also serve as modifiers of enzymatic activity, whether inhibition or stimulation. Polyphenol oxidases (PPO) and peroxidases (POD) use phenolic compounds as substrates in oxidative browning. Apple browning leads to flesh color, taste, texture, and flavor degradation, representing a drawback for the variety and its' market appraisal. This study was conducted to investigate the process of browning in 14 apple cultivars throughout post-harvest at three-time points: immediately (T0), one hour (T1), and 24 h (T2) after apples were cut in half. Color parameters L* (lightness), a* (red/green), b* (yellow/blue) were measured, and chroma (ΔC*) and color (ΔE) were calculated to quantify differences between T0₋T1 and T1₋T2 on the fruit surface. Enzymatic activity (PPO, POD) and phenolic composition were also quantified for each cultivar. 'Granny Smith' and 'Cripps Pink' browned minimally. In contrast, 'Fiesta' and 'Mondial Gala' browned severely, reporting high enzymatic activity and quantified phenolic concentration (QPC). Phenolic compound polymerization appears to play a significant role in enzymatic inhibition. 'Topaz' does not fit the high QPC, PPO, and browning formula, suggesting alternative pathways that contribute to apple browning.