Proregenerative extracellular matrix hydrogel mitigates pathological alterations of pelvic skeletal muscles after birth injury

Recent Development of Fibrous Hydrogels: Properties, Applications and Perspectives

Fibrous hydrogels (FGs), characterized by a 3D network structure made from prefabricated fibers, fibrils and polymeric materials, have emerged as significant materials in numerous fields. However, the challenge of balancing mechanical properties and functions hinders their further development. This article reviews the main advantages of FGs, including enhanced mechanical properties, high conductivity, high antimicrobial and anti-inflammatory properties, stimulus responsiveness, and an extracellular matrix (ECM)-like structure. It also discusses the influence of assembly methods, such as fiber cross-linking, interfacial treatments of fibers with hydrogel matrices, and supramolecular assembly, on the diverse functionalities of FGs. Furthermore, the mechanisms for improving the performance of the above five aspects are discussed, such as creating ion carrier channels for conductivity, in situ gelation of drugs to enhance antibacterial and anti-inflammatory properties, and entanglement and hydrophobic interactions between fibers, resulting in ECM-like structured FGs. In addition, this review addresses the application of FGs in sensors, dressings, and tissue scaffolds based on the synergistic effects of optimizing the performance. Finally, challenges and future applications of FGs are discussed, providing a theoretical foundation and new insights for the design and application of cutting-edge FGs.

Mechanical Stress-Oxidative Stress Axis: Biological Basis in the Vaginal Wall and Pelvic Floor Muscles of Rats with Simulated Birth Injury

INTRODUCTION AND HYPOTHESIS

Vaginal delivery and resulting pelvic floor muscle (PFM) dysfunction are significant risk factors for pelvic floor dysfunction (PFD). Despite this, the biological basis underlying PFD after childbirth remain unclear. This study was aimed at assessing the early response of the vaginal wall and PFM to simulated birth injury (SBI) in rats.

METHODS

Forty female Sprague-Dawley rats were divided into four groups: control (sham operation), and 1, 4, and 14 days post-injury. In the SBI groups, a catheter was inserted into the vagina with 130 g of weight attached to the end, and the balloon was inflated to 5 ml for 2 h. Evaluation of vaginal tissues and PFMs included histological, immunohistochemical, Western blot, and uniaxial biomechanical testing.

RESULTS

In the vaginal wall, the SBI group showed significantly lower COL1A1 expression and higher MMP-2 and MMP-9 expression. At 4 and 14 days post-injury, there was a significant decrease in PFM fiber area and increased collagen content. The SBI group also exhibited significant increases in the expression of Nrf2, NQO1, HO-1, and SOD-2, indicating involvement of oxidative stress in both the vaginal wall and PFMs. Protein expression of Pax7 and MyoG, as well as the number of fibers with centralized nuclei, continued to increase significantly after SBI. Additionally, the vaginal wall of the SBI group showed a decreasing trend in tensile strength and elastic modulus, with a greater ultimate strain.

CONCLUSION

Extracellular matrix remodeling, oxidative stress, decreased biomechanical properties, and muscle dysmyogenesis may collectively contribute to increased susceptibility to PFD development.

Repeated birth injuries lead to long-term pelvic floor muscle dysfunction in the preclinical rat model

BACKGROUND

Vaginal childbirth is a key risk factor for pelvic floor muscle injury and dysfunction, and subsequent pelvic floor disorders. Multiparity further exacerbates these risks. Using the rat model, validated for the studies of the human pelvic floor muscles, we have previously identified that a single simulated birth injury results in pelvic floor muscle atrophy and fibrosis.

OBJECTIVE

To test the hypothesis that multiple birth injuries would further overwhelm the muscle regenerative capacity, leading to functionally relevant pathological alterations long-term.

STUDY DESIGN

Sprague-Dawley rats underwent simulated birth injury and were allowed to recover for 8 weeks before undergoing additional birth injury. Animals were sacrificed at acute (3 and 7 days postinjury), subacute (21, 28, and 35 days postinjury), and long-term (8 and 12 weeks postinjury) time points post second injury (N=3-8/time point), and the pubocaudalis portion of the rat levator ani complex was harvested to assess the impact of repeated birth injuries on muscle mechanical and histomorphological properties. The accompanying transcriptional changes were assessed by a customized NanoString panel. Uninjured animals were used as controls. Data with a parametric distribution were analyzed by a 2-way analysis of variance followed by post hoc pairwise comparisons using Tukey's or Sidak's tests; nonparametrically distributed data were compared with Kruskal-Wallis test followed by pairwise comparisons with Dunn's test. Data, analyzed using GraphPad Prism v8.0, San Diego, CA, are presented as mean ± standard error of the mean or median (range).

RESULTS

Following the first simulated birth injury, active muscle force decreased acutely relative to uninjured controls (12.9±0.9 vs 25.98±2.1 g/mm2, P<.01). At 4 weeks, muscle active force production recovered to baseline and remained unchanged at 8 weeks after birth injury (P>.99). Similarly, precipitous decrease in active force was observed immediately after repeated birth injury (18.07±1.2 vs 25.98±2.1 g/mm2, P<.05). In contrast to the functional recovery after a single birth injury, a long-term decrease in muscle contractile function was observed up to 12 weeks after repeated birth injuries (18.3±1.6 vs 25.98±2.1 g/mm2, P<.05). Fiber size was smaller at the long-term time points after second injury compared to the uninjured group (12 weeks vs uninjured control: 1485 (60.7-5000) vs 1989 (65.6-4702) μm2, P<.0001). The proportion of fibers with centralized nuclei, indicating active myofiber regeneration, returned to baseline at 8 weeks post-first birth injury, (P=.95), but remained elevated as far as 12 weeks post-second injury (12 weeks vs uninjured control: 7.1±1.5 vs 0.84±0.13%, P<0.0001). In contrast to the plateauing intramuscular collagen content after 4 weeks post-first injury, fibrotic degeneration increased progressively over 12 weeks after repeated injury (12 weeks vs uninjured control: 6. 7±1.1 vs 2.03±0.2%, P<.001). Prolonged expression of proinflammatory genes accompanied by a greater immune infiltrate was observed after repeated compared to a single birth injury.

CONCLUSION

Overall, repeated birth injuries lead to a greater magnitude of pathological alterations compared to a single injury, resulting in more pronounced pelvic floor muscle degeneration and muscle dysfunction in the rat model. The above provides a putative mechanistic link between multiparity and the increased risk of pelvic floor dysfunction in women.

Regenerative Medicine in Gynecology

The female reproductive tract undergoes dynamic changes across the life span. Congenital abnormalities, life events, and medical interventions can negatively affect the structure and function of reproductive tract organs, resulting in lifelong sequelae. The objective of regenerative gynecology is to discover and promote endogenous mechanisms by which a healthy tissue maintains overall tissue integrity after injury, after disease, or with age. In this review, we discuss some of the key state-of-the-art cell-based and scaffolding therapies that have been applied to regenerate gynecologic tissues and organs primarily in animal and tissue culture models. We further discuss the limitations of current technologies, problems of implementation and scalability, and future outlook of the field.

Tracking of Nascent Matrix Deposition during Muscle Stem Cell Activation across Lifespan Using Engineered Hydrogels

Adult stem cells occupy a niche that contributes to their function, but how stem cells rebuild their microenvironment after injury remains an open-ended question. Herein, biomaterial-based systems and metabolic labeling are utilized to evaluate how skeletal muscle stem cells deposit extracellular matrix. Muscle stem cells and committed myoblasts are observed to generate less nascent matrix than muscle resident fibro-adipogenic progenitors. When cultured on substrates that matched the stiffness of physiological uninjured and injured muscles, muscle stem cells increased nascent matrix deposition with activation kinetics. Reducing the ability to deposit nascent matrix by an inhibitor of vesicle trafficking (Exo-1) attenuated muscle stem cell function and mimicked impairments observed from muscle stem cells isolated from old muscles. Old muscle stem cells are observed to deposit less nascent matrix than young muscle stem cells, which is rescued with therapeutic supplementation of insulin-like growth factors. These results highlight the role of nascent matrix production with muscle stem cell activation.

Regenerative Medicine in Urogynecology: Where We Are and Where We Want to Be

ABSTRACT

Pelvic floor disorders (PFDs) constitute a major public health issue given their negative effect on quality of life for millions of women worldwide and the associated economic burden. As the prevalence of PFDs continues to increase, novel therapeutic approaches for the effective treatment of these disorders are urgently needed. Regenerative medicine techniques, including cellular therapies, extracellular vesicles, secretomes, platelet-rich plasma, laser therapy, and bioinductive acellular biomaterial scaffolds, are emerging as viable clinical options to counteract urinary and fecal incontinence, as well as pelvic organ prolapse. This brief expert review explores the current state-of-science regarding application of these therapies for the treatment of PFDs. Although regenerative approaches have not been widely deployed in clinical care to date, these innovative techniques show a promising safety profile and potential to positively affect the quality of life of patients with PFDs. Furthermore, investigations focused on regeneration of the main constituents of the pelvic floor and lower urinary tract improve our understanding of the underlying pathophysiology of PFDs. Regenerative medicine techniques have a high potential not only to revolutionize treatment of PFDs but also to prevent these complex conditions.

Shift from Pro- to Anti-Inflammatory Phase in Pelvic Floor Muscles at Postpartum Matches Histological Signs of Regeneration in Multiparous Rabbits

Background and Objectives: Pelvic floor muscles (PFM) play a core role in defecation and micturition. Weakening of PFM underlies urogynecological disorders such as pelvic organ prolapse and stress urinary incontinence. Vaginal delivery damages PFM. Muscle trauma implies an inflammatory response mediated by myeloid cells, essential for subsequent recovery. Molecular signaling characterizing the pro-inflammatory phase shifts M1 macrophages to M2 macrophages, which modulate muscle repair. The present study aimed to evaluate histological characteristics and the presence of M1 and M2 macrophages in bulbospongiosus (Bsm) and pubococcygeus muscles (Pcm). Materials and Methods: Muscles from young nulliparous (N) and multiparous rabbits on postpartum days three (M3) and twenty (M20) were excised and histologically processed to measure the myofiber cross-sectional area (CSA) and count the centralized myonuclei in hematoxylin-eosinstained sections. Using immunohistochemistry, M1 and M2 macrophages were estimated in muscle sections. Kruskal-Wallis or one-way ANOVA testing, followed by post hoc tests, were conducted to identify significant differences (p < 0.05). Results: The myofiber CSA of both the Bsm and Pcm of the M3 group were more extensive than those of the N and M20 groups. Centralized myonuclei estimated in sections from both muscles of M20 rabbits were higher than those of N rabbits. Such histological outcomes matched significant increases in HLA-DR immunostaining in M3 rabbits with the CD206 immunostaining in muscle sections from M20 rabbits. Conclusions: A shift from the pro- to anti-inflammatory phase in the bulbospongiosus and pubococcygeus muscles of multiparous rabbits matches with centralized myonuclei, suggesting the ongoing regeneration of muscles.

Beyond Traditional Medicine: EVs-Loaded Hydrogels as a Game Changer in Disease Therapeutics

Extracellular vesicles (EVs), especially exosomes, have shown great therapeutic potential in the treatment of diseases, as they can target cells or tissues. However, the therapeutic effect of EVs is limited due to the susceptibility of EVs to immune system clearance during transport in vivo. Hydrogels have become an ideal delivery platform for EVs due to their good biocompatibility and porous structure. This article reviews the preparation and application of EVs-loaded hydrogels as a cell-free therapy strategy in the treatment of diseases. The article also discusses the challenges and future outlook of EVs-loaded hydrogels.

Quantification of local matrix deposition during muscle stem cell activation using engineered hydrogels

Adult stem cells occupy a niche that contributes to their function, but how stem cells remodel their microenvironment remains an open-ended question. Herein, biomaterials-based systems and metabolic labeling were utilized to evaluate how skeletal muscle stem cells deposit extracellular matrix. Muscle stem cells and committed myoblasts were observed to generate less nascent matrix than muscle resident fibro-adipogenic progenitors. When cultured on substrates that matched the stiffness of physiological uninjured and injured muscles, the increased nascent matrix deposition was associated with stem cell activation. Reducing the ability to deposit nascent matrix in muscle stem cells attenuated function and mimicked impairments observed from muscle stem cells isolated from old aged muscles, which could be rescued with therapeutic supplementation of insulin-like growth factors. These results highlight how nascent matrix production is critical for maintaining healthy stem cell function.