Cellular senescence and wound healing in aged and diabetic skin

Matrix viscoelasticity drives cell cluster formation to counteract cellular senescence

During tissue repair, stress-induced cellular senescence represents a critical factor that impedes the regenerative potential of tissues. While the regulatory effects of matrix viscoelasticity on cellular behavior have been documented, their role and correlated mechanisms underlying cellular senescence remain unclear. In this study, we engineered a viscoelastic gel matrix exhibiting a storage modulus of approximately 3 kPa, with a tunable loss modulus ranging from 0 to 300 Pa by incorporating linear alginate and modulating the compactness of a polyacrylamide-based covalent network. Utilizing a UV-induced senescence model, we observed that increasing the matrix's viscoelasticity from 0 Pa to 300 Pa led to a significant reduction in the proportion of senescent cells, from 90.5% to 22.7%. Furthermore, cells cultured in these matrices exhibited a tendency to form cell aggregation, with the cell populations demonstrating a collective resistance to stresses. This indicated that viscoelastic materials would promote enhanced cellular interactions, thereby strengthening cellular resilience against UV-induced stresses. Furthermore, combined with microarray analysis, it was concluded that the presence of viscoelastic components activated the connexin 43 (Cx43)-modulated gap junction for cluster formation, thereby suppressing the senescence-associated signaling pathways, including Wnt/β-catenin, MAPK, NF-κB, and TGF-β. Additionally, the integrin-cytoskeleton-Yes-associated protein (YAP) signaling axis played an active role in delaying cell aging. These results provide novel insights into the regulatory role of viscoelastic materials in cellular senescence and offer a compelling foundation for the development of advanced biomaterials for tissue repair.

Analysis of the senescence secretome during zebrafish retina regeneration

Introduction

Zebrafish possess the innate ability to regenerate any lost or damaged retinal cell type with Müller glia serving as resident stem cells. Recently, we discovered that this process is aided by a population of damage-induced senescent immune cells. As part of the Senescence Associated Secretory Phenotype (SASP), senescent cells secrete numerous factors that can play a role in the modulation of inflammation and remodeling of the retinal microenvironment during regeneration. However, the identity of specific SASP factors that drive initiation and progression of retina regeneration remains unclear.

Materials and Methods

We mined the SASP Atlas and publicly available RNAseq datasets to identify common, differentially expressed SASP factors after retina injury. These datasets included two distinct acute damage regimens, as well as two chronic, genetic models of retina degeneration. We identified overlapping factors between these models and used genetic knockdown experiments, qRT/PCR and immunohistochemical staining to test a role for one of these factors (npm1a).

Results

We discovered an overlapping set of 31 SASP-related regeneration factors across all data sets and damage paradigms. These factors are upregulated after damage with functions that span the innate immune system, autophagic processing, cell cycle regulation, and cellular stress responses. From among these, we show that depletion of Nucleophosmin 1 (npm1a) inhibits retina regeneration and decreases senescent cell detection after damage.

Discussion

Our data suggest that differential expression of SASP factors promotes initiation and progression of retina regeneration after both acute and chronic retinal damage. The existence of a common, overlapping set of 31 factors provides a group of novel therapeutic targets for retina regeneration studies.

Senescence as a molecular target in skin aging and disease

Skin aging represents a multifactorial process influenced by both intrinsic and extrinsic factors, collectively known as the skin exposome. Cellular senescence, characterized by stable cell cycle arrest and secretion of pro-inflammatory molecules, has been implicated as a key driver of physiological and pathological skin aging. Increasing evidence points towards the role of senescence in a variety of dermatological diseases, where the accumulation of senescent cells in the epidermis and dermis exacerbates disease progression. Emerging therapeutic strategies such as senolytics and senomorphics offer promising avenues to target senescent cells and mitigate their deleterious effects, providing potential treatments for both skin aging and senescence-associated skin diseases. This review explores the molecular mechanisms of cellular senescence and its role in promoting age-related skin changes and pathologies, while compiling the observed effects of senotherapeutics in the skin and discussing the translational relevance.

Spiny mice (Acomys) have evolved cellular features to support regenerative healing

Spiny mice (Acomys spp.) are warm-blooded (homeothermic) vertebrates whose ability to restore missing tissue through regenerative healing has coincided with the evolution of unique cellular and physiological adaptations across different tissue types. This review seeks to explore how these bizarre rodents deploy unique or altered injury response mechanisms to either enhance tissue repair or fully regenerate excised tissue compared to closely related, scar-forming mammals. First, we examine overall trends in healing Acomys tissues, including the cellular stress response, the ability to activate and maintain cell cycle progression, and the expression of certain features in reproductive adults that are normally associated with embryos. Second, we focus on specific cell types that exhibit precisely regulated proliferation to restore missing tissue. While Acomys utilize many of the same cell types involved in scar formation, these cells exhibit divergent activation profiles during regenerative healing. Considered together, current lines of evidence support sustained deployment of proregenerative pathways in conjunction with transient activation of fibrotic pathways to facilitate regeneration and improve tissue repair in Acomys.

Peptide Nanofibers and Skin Regeneration

Peptide nanofibers have been attractive targets for regenerative medicine applications due to their tailorability to be easily functionalized for specific bioactivity, biocompatibility, ease of synthesis, adjustability of their physicochemical characteristics, and lack of biological contamination. Research groups have investigated their use for the regeneration of various tissues, such as bone, cartilage, brain, peripheral nerves, cardiac tissue, vascular tissues, endocrine cells, muscles, etc., for the treatment of degenerative diseases or tissue loss due to accidents or aging. Wound healing and skin regeneration are among the most widely investigated research areas for peptide nanofibers as well. In this article, we reviewed the literature on the utilization of peptide nanofibers for various skin regeneration and dermal healing applications, aiming to give the readers a general view of how peptide nanofibers have been used for this purpose so far as well as provide new insight on which avenues more research is necessary to be able to apply these methods in clinics.

Immune Aging in Rheumatoid Arthritis

Rheumatoid arthritis (RA) is a life-long autoimmune disease caused by the confluence of genetic and environmental variables that lead to loss of self-tolerance and persistent joint inflammation. RA occurs at the highest incidence in individuals >65 years old, implicating the aging process in disease susceptibility. Transformative approaches in molecular immunology and in functional genomics have paved the way for pathway paradigms underlying the replacement of immune homeostasis with autodestructive immunity in affected patients, including the process of immune aging. Patients with RA have a signature of premature immune aging, best understood for CD4+ T cells, which function as pathogenic effectors in this HLA class II-associated disease. Premature immune aging is present in healthy HLA-DRB1*04+ individuals, placing accelerated immune aging before joint inflammation. Aging-related molecular abnormalities directly implicated in turning RA CD4+ T cells into proinflammatory effector cells are linked to malfunction of subcellular organelles, such as mitochondria, lysosomes, lipid droplets, and the endoplasmic reticulum. Resulting changes in T cell behavior include cellular hypermobility, tissue invasiveness, unopposed mammalian target of rapamycin complex (mTORC)1 activation, excessive release of tumor necrosis factor, lysosomal failure, clonal expansion, and immunogenic cell death. Aged and metabolically reprogrammed T cells in patients with RA are accompanied by age-associated B cells, which specialize in autoantibody production. Clonal hematopoiesis drives myeloid cell aging by producing aged monocytes and hypermetabolic macrophages, which sustain the process of inflammaging. Here, we synthesize insights into the relationship of RA risk and immune aging and discuss mechanisms through which immune aging can cause autoimmunity.

Topical ABT-263 treatment reduces aged skin senescence and improves subsequent wound healing

Senescent cells accumulate in aging tissues, impairing their ability to undergo repair and regeneration following injury. Previous research has demonstrated that targeting tissue senescence with senolytics can enhance tissue regeneration and repair by selectively eliminating SnCs in specific aged tissues. In this study, we focused on eliminating senescent skin cells in aged mice to assess the effects on subsequent wound healing. We applied ABT-263 directly to the skin of 24-month-old mice over a 5-day period. Following topical ABT-263, aged skin demonstrated decreased gene expression of senescence markers p16 and p21, accompanied by reductions in SA-β-gal- and p21-positive cells compared to DMSO controls. However, ABT-263 also triggered a temporary inflammatory response and macrophage infiltration in the skin. Bulk RNA sequencing of ABT-263-treated skin revealed prompt upregulation of genes associated with wound healing pathways, including hemostasis, inflammation, cell proliferation, angiogenesis, collagen synthesis, and extracellular matrix organization. Aged mice skin pre-treated with topical ABT-263 exhibited accelerated wound closure. In conclusion, topical ABT-263 effectively reduced several senescence markers in aged skin, thereby priming the skin for improved subsequent wound healing. This enhancement may be attributed to ABT-263-induced senolysis which in turn stimulates the expression of genes involved in extracellular matrix remodeling and wound repair pathways.

Clearance of senescent cells enhances skin wound healing in type 2 diabetic mice

Background: Diabetic foot ulcers (DFUs) pose a substantial healthcare challenge due to their high rates of morbidity, recurrence, disability, and mortality. Current DFU therapeutics continue to grapple with multiple limitations. Senescent cells (SnCs) have been found to have a beneficial effect on acute wound healing, however, their roles in chronic wounds, such as DFU, remain unclear. Methods and results: We collected skin, fat, and muscle samples from clinical patients with DFU and lower limb fractures. RNA-sequencing combined with qPCR analyses on these samples demonstrate a significant accumulation of SnCs at DFU, as indicated by higher senescence markers (e.g., p16 and p21) and a senescence-associated secretory phenotype (SASP). We constructed a type 2 diabetic model of db/db mice, fed with a high-fat diet (Db-HFD), which were wounded using a 6 mm punch to the dorsal skin. HFD slightly affected wound healing in wild-type (WT) mice, but high glucose significantly delayed wound healing in the Db-HFD mice. We injected the mice with a previously developed fluorescent probe (XZ1208), which allows the detection of SnCs in vivo, and observed a strong senescence signal at the wound site of the Db-HFD mice. Contrary to the beneficial effects of SnCs in acute wound healing, our results demonstrated that clearance of SnCs using the senolytic compound ABT263 significantly accelerated wound healing in Db-HFD mice. Conclusion: Collectively, these findings suggest that SnCs critically accumulate at wound sites, delaying the healing process in DFUs. Thus, targeting SnCs with senolytic therapy represents a promising approach for DFU treatment, potentially improving the quality of life for patients with DFUs.

Topical ABT-263 treatment reduces aged skin senescence and improves subsequent wound healing

Senescent cells (SnC) accumulate in aging tissues, impairing their ability to undergo repair and regeneration following injury. Previous research has demonstrated that targeting tissue senescence with senolytics can enhance tissue regeneration and repair by selectively eliminating SnCs in specific aged tissues. In this study, we focused on eliminating SnC skin cells in aged mice to assess the effects on subsequent wound healing. We applied ABT-263 directly to the skin of 24-month-old mice over a 5-day period. Following topical ABT-263, aged skin demonstrated decreased gene expression of senescent markers p16 and p21, accompanied by reductions in SA-β-gal and p21-positive cells compared to DMSO controls. However, ABT-263 also triggered a temporary inflammatory response and macrophage infiltration in the skin. Bulk RNA sequencing of ABT-263-treated skin revealed prompt upregulation of genes associated with wound healing pathways, including hemostasis, inflammation, cell proliferation, angiogenesis, collagen synthesis, and extracellular matrix organization. Aged mice skin pre-treated with topical ABT-263 exhibited accelerated wound closure. In conclusion, topical ABT-263 effectively reduced several senescence markers in aged skin, thereby priming the skin for improved subsequent wound healing. This enhancement may be attributed to ABT-263-induced senolysis which in turn stimulates the expression of genes involved in extracellular matrix remodeling and wound repair pathways.

Treatment of anal fistulas with Obsidian RFT®: just another autologous compound platelet-rich fibrin foam?

BACKGROUND

Sphincter-preserving techniques like autologous compound platelet-rich fibrin foam have gained popularity, offering potential for better functional outcomes in anal fistula treatment. The present study aimed to evaluate the efficacy and safety of Obsidian RFT®.

METHODS

The study conducted a retrospective analysis from January 2018 to December 2022 on patients who received anal fistula closure with Obsidian RTF® at the Department of General Surgery, Medical University of Vienna. Clinical diagnosis, complemented by radiographic imaging, was employed to confirm inconclusive cases. Demographic and fistula characteristics and postoperative data were collected from electronic records following STROCSS criteria.

RESULTS

Fifteen patients received Obsidian RFT® treatment for anal fistulas. We found no intra- and postoperative complications. The median hospital stay was 3 days. After a median follow-up of 32 months, a closure rate of 53.3% was detected. Non-significant differences were observed in various variables, yet trends emerged, indicating associations between abscess presence and non-healing fistulas. A distinct age threshold (≥ 42.7 years) served as an indicator for an inability to achieve anal fistula cure.

CONCLUSION

Obsidian RFT® represents a safe, minimally invasive operative procedure. Approximately half the patients experienced healing, with better outcome in a younger population.

TRIAL REGISTRATION

Ethical Approval number Medical University of Vienna (#1258/2018). This study was registered retrospectively in ClinicalTrials.gov (NCT06136325).

Targeting senescent cells to reshape the tumor microenvironment and improve anticancer efficacy

Cancer is daunting pathology with remarkable breadth and scope, spanning genetics, epigenetics, proteomics, metalobomics and cell biology. Cellular senescence represents a stress-induced and essentially irreversible cell fate associated with aging and various age-related diseases, including malignancies. Senescent cells are characterized of morphologic alterations and metabolic reprogramming, and develop a highly active secretome termed as the senescence-associated secretory phenotype (SASP). Since the first discovery, senescence has been understood as an important barrier to tumor progression, as its induction in pre-neoplastic cells limits carcinogenesis. Paradoxically, senescent cells arising in the tumor microenvironment (TME) contribute to tumor progression, including augmented therapeutic resistance. In this article, we define typical forms of senescent cells commonly observed within the TME and how senescent cells functionally remodel their surrounding niche, affect immune responses and promote cancer evolution. Furthermore, we highlight the recently emerging pipelines of senotherapies particularly senolytics, which can selectively deplete senescent cells from affected organs in vivo and impede tumor progression by restoring therapeutic responses and securing anticancer efficacies. Together, co-targeting cancer cells and their normal but senescent counterparts in the TME holds the potential to achieve increased therapeutic benefits and restrained disease relapse in future clinical oncology.

Revolutionizing Diabetic Foot Ulcer Care: The Senotherapeutic Approach

Diabetic foot ulcers (DFUs) are a prevalent and profoundly debilitating complication that afflicts individuals with diabetes mellitus (DM). These ulcers are associated with substantial morbidity, recurrence rates, disability, and mortality, imposing substantial economic, psychological, and medical burdens. Timely detection and intervention can mitigate the morbidity and disparities linked to DFU. Nevertheless, current therapeutic approaches for DFU continue to grapple with multifaceted limitations. A growing body of evidence emphasizes the crucial role of cellular senescence in the pathogenesis of chronic wounds. Interventions that try to delay cellular senescence, eliminate senescent cells (SnCs), or suppress the senescence-associated secretory phenotype (SASP) have shown promise for helping chronic wounds to heal. In this context, targeting cellular senescence emerges as a novel therapeutic strategy for DFU. In this comprehensive review, we look at the pathology and treatment of DFU in a systematic way. We also explain the growing importance of investigating SnCs in DFU and highlight the great potential of senotherapeutics that target SnCs in DFU treatment. The development of efficacious and safe senotherapeutics represents a pioneering therapeutic approach aimed at enhancing the quality of life for individuals affected by DFU.

Research Progress in Skin Aging and Immunity

Skin aging is a complex process involving structural and functional changes and is characterized by a decrease in collagen content, reduced skin thickness, dryness, and the formation of wrinkles. This process is underpinned by multiple mechanisms including the free radical theory, inflammation theory, photoaging theory, and metabolic theory. The skin immune system, an indispensable part of the body's defense mechanism, comprises macrophages, lymphocytes, dendritic cells, and mast cells. These cells play a pivotal role in maintaining skin homeostasis and responding to injury or infection. As age advances, along with various internal and external environmental stimuli, skin immune cells may undergo senescence or accelerated aging, characterized by reduced cell division capability, increased mortality, changes in gene expression patterns and signaling pathways, and altered immune cell functions. These changes collectively impact the overall function of the immune system. This review summarizes the relationship between skin aging and immunity and explores the characteristics of skin aging, the composition and function of the skin immune system, the aging of immune cells, and the effects of these cells on immune function and skin aging. Immune dysfunction plays a significant role in skin aging, suggesting that immunoregulation may become one of the important strategies for the prevention and treatment of skin aging.

Stem Cells and Nanofibers for Skin Regeneration and Wound Healing

Stem cells have been attractive targets for tissue regeneration due to their inherent ability to differentiate into various specialized cell types; however, efforts for stem cell transplantation for the treatment of degenerated tissues have been hampered by the propensity of some stem cell types to form teratomas and the lessened viability of stem cells after transplantation. These disadvantages can be prevented using tailored extracellular matrix-like materials that can be used as an aid for the transplantation of stem cells. Nanomaterials, in particular nanofibers, have great potential to be used as extracellular matrix-like materials for this purpose. In this article, we will review the use of stem cells and nanofibers for skin regeneration and wound healing.