The panniculus carnosus muscle: an evolutionary enigma at the intersection of distinct research fields

Biocompatibility and wound-healing prospect of KAPs-depleted residual hair biomaterial

This work is an in-depth investigation of the in vitro and in vivo biocompatibility of processed and treated residual human hair samples with intact cuticle layers. The specimens included oxidized hair with minimal melanin (BLH) and hair with medium- (M-KAP) and low- (L-KAP) amounts of keratin associated proteins (KAPs), confirmed through gel electrophoresis, electron microscopy, trichrome histological staining, and tensile biomechanics, in comparison to the untreated regular hair (REG) control. All hair groups, high KAPs (H-KAPs: REG and BLH), M-KAP, and L-KAP, are non-cytotoxic in the adipose fibroblast's response to their extracts based on the ISO 10993-5 medical device biomaterial testing standard. In vivo mouse subcutaneous implantation (ISO 10993-6, local effects) at 2 weeks showed a foreign body response (FBR) with thin fibrous encapsulation at 28% relative skin dermis thickness; but the L-KAP implant mitigated a significant decrease in FBR area compared to H-KAPs and a lower number of immune cells of mostly macrophages and mast cells on the biomaterial's surface. In the bulk of the capsules, blood vessels and collagen extracellular matrix densities were similar among groups. These findings suggest that small globular KAPs diffuse out of the cortex to the host-biomaterial interface which induce a slightly-elevated FBR but limited to the implant's surface vicinity. For translatability, we evaluated the effectiveness of the residual hair with the most depleted KAPs (L-KAP) in a 10 mm-diameter, splinted, and full-thickness mouse skin excision wound. Treatment with the L-KAP mesh exhibited an 8% healing improvement per day compared to the untreated control: significantly reducing the projected complete healing time by 30%. On-going research focuses on purer keratin-based and macromolecularly organized residual hair biomaterials for drug-delivery as they are deemed the most biocompatible.

Prevalence of behavioural signs commonly associated with feline hyperaesthesia syndrome among healthy cats

OBJECTIVES

The most common clinical signs of feline hyperaesthesia syndrome are rolling skin and behavioural abnormalities (e.g. licking or biting the tail, flanks, anal region or lumbar region). This study aimed to determine the prevalence of behavioural signs commonly associated with feline hyperaesthesia syndrome among healthy cats.

MATERIALS AND METHODS

This descriptive cross-sectional bicentric prospective study included 208 healthy cats that presented for vaccination. A survey about the cats' behaviour was completed by caregivers and six general practice veterinarians.

RESULTS

Seventy-three per cent of the cats presented at least one behavioural sign of feline hyperaesthesia syndrome. Only 26.9% of the caregivers report zero behavioural of feline hyperaesthesia syndrome at home. Eighty per cent of the indoor-only cats and 65.3% of the outdoor cats had at least one behavioural sign (odds ratio 2.08, 95% confidence interval 1.12 to 3.88). Thirty-one per cent of the cats reacted to lumbar palpation by veterinarians, and 18.7% of these cats were not reported to present signs of feline hyperaesthesia syndrome at home.

CLINICAL SIGNIFICANCE

In this population of healthy cats, 73.1% of cats consistently displayed at least one behavioural sign of feline hyperaesthesia syndrome at home. Adverse reactions after lumbar palpation by a veterinarian were also reported in healthy cats, including cats without behavioural signs at home. The results suggest that many of these behavioural signs have no diagnostic value in isolation. A scoring system could be used to differentiate cats with feline hyperaesthesia syndrome from cats with normal behaviour.

Towards a consensus atlas of human and mouse adipose tissue at single-cell resolution

Adipose tissue (AT) is a complex connective tissue with a high relative proportion of adipocytes, which are specialized cells with the ability to store lipids in large droplets. AT is found in multiple discrete depots throughout the body, where it serves as the primary repository for excess calories. In addition, AT has an important role in functions as diverse as insulation, immunity and regulation of metabolic homeostasis. The Human Cell Atlas Adipose Bionetwork was established to support the generation of single-cell atlases of human AT as well as the development of unified approaches and consensus for cell annotation. Here, we provide a first roadmap from this bionetwork, including our suggested cell annotations for humans and mice, with the aim of describing the state of the field and providing guidelines for the production, analysis, interpretation and presentation of AT single-cell data.

Development of an ex vivo human skin model and evaluation of biological responses to subcutaneously injected hyaluronic acid formulations

We have previously described a model using porcine ear skin ex vivo for longitudinal studies into the disposition of macromolecules after subcutaneous injection. Since porcine skin cannot fully mimic biological responses in human skin, we now describe an ex vivo system using "full thickness" human skin. Spongiosis and epidermal detachment were the primary endpoints to evaluate skin structural integrity over a 9-day culture period. Epidermal barrier function and basal cell proliferation were monitored using expression of claudin-1 and Ki-67, respectively. Immunofluorescent staining of type I and type III procollagens and elastin after subcutaneous injection of TGF-β3, a cross-linked hyaluronic acid hydrogel, and saline solution and "no treatment" controls, showed that the model enabled visualization of changes in extracellular matrix proteins. Semi-quantitative, automated image analysis methods using multiple ROIs were evaluated to assess signal intensity and expression area of type I procollagen but displayed high inter-regional variability due to skin sample heterogeneity. Absolute quantitative methods, e.g. RT-qPCR or ELISA, which enable determination of biomarkers at either the mRNA level or the amounts of protein expressed in the sample, could be a better reporting tool. In conclusion, we successfully developed an ex vivo "full thickness" human skin model that retained viability over 9 days and which could be deployed in combination with qualitative/quantitative methods to evaluate local biological effects of subcutaneously injected biomacromolecules.

A novel mouse model for studies of burn wound conversion using a top hat-shaped brass template

INTRODUCTION

The pathophysiology of burn wound conversion is not fully understood. Animal models are needed to elucidate the underlying mechanisms and develop treatments. Here, we established a new reproducible mouse model that simulates this process, thereby facilitating studies of burn wound conversion.

MATERIALS AND METHODS

After anesthesia and depilation, 75 mice were randomly assigned to 5-, 15-, and 25-s contact groups, and a top hat-shaped brass template was heated in boiling water and applied to the lateral abdomen. The wound area was calculated from photographs and the percentage of the surviving area was determined. Histological samples were collected 1-96 h after injury.

RESULTS

A 15-s contact time produced the desired 50 %-75 % interspace necrosis at 96 h after injury. The 5-s contact group had a mostly preserved interspace, while the 25-s contact group exhibited near-complete necrosis. Histologically, significant differences between the 5- and 15-s contact groups were seen in cutaneous appendage denaturation and panniculus carnosus denaturation early after injury.

CONCLUSION

Exposing mice to the heated template for 15 s provides a reproducible model for studying burn wound conversion mechanisms and treatments, facilitating further elucidation of burn pathophysiology and evaluation of therapies to prevent burn wound conversion.

Ventral body wall closure: Mechanistic insights from mouse models and translation to human pathology

The ventral body wall (VBW) that encloses the thoracic and abdominal cavities arises by extensive cell movements and morphogenetic changes during embryonic development. These morphogenetic processes include embryonic folding generating the primary body wall; the initial ventral cover of the embryo, followed by directed mesodermal cell migrations, contributing to the secondary body wall. Clinical anomalies in VBW development affect approximately 1 in 3000 live births. However, the cell interactions and critical cellular behaviors that control VBW development remain little understood. Here, we describe the embryonic origins of the VBW, the cellular and morphogenetic processes, and key genes, that are essential for VBW development. We also provide a clinical overview of VBW anomalies, together with environmental and genetic influences, and discuss the insight gained from over 70 mouse models that exhibit VBW defects, and their relevance, with respect to human pathology. In doing so we propose a phenotypic framework for researchers in the field which takes into account the clinical picture. We also highlight cases where there is a current paucity of mouse models for particular clinical defects and key gaps in knowledge about embryonic VBW development that need to be addressed to further understand mechanisms of human VBW pathologies.

Morphological Investigation of Superficial Fascia Relationships With the Skin and Underlying Tissues in the Canine Hindlimb

The morphology of the superficial fascia in the canine hindlimb is still poorly understood and incompletely described. The present study aimed to elucidate the macroscopic and microscopic structures of the superficial fascia, thereby clarifying its functional role. Cadavers were investigated for anatomic description (N = 38), ultrasonic scanning (N = 2), and histological analyses (N = 10) of this tissue in the hindlimb. The superficial fascia was identified as a shiny, white fibroelastic layer that adhered to the skin through fibrous septa. It was organized into sublayers enveloping the cutaneous muscle and large blood vessels. In certain areas, superficial fascia fused with the deep fascia or skin, creating fascial bursae. These bursae included the ischiatic bursa, an iliac bursa, a prepatellar subfascial bursa, a prepatellar subcutaneous bursa, and the tarsal fascial bursa. Microscopically, the superficial fascia presented as a layer of dense connective tissue characterized by irregularly arranged collagen and elastic fibers. The superficial fascia was firmly attached to the skin and deep fascia by numerous fibrous tissue strands. Within both, the superficial fascia and fascial bursae, several mechanoreceptors and nerve endings were identified, including Ruffini's corpuscles, Pacinian corpuscles, and Golgi-Mazzoni corpuscles. The organization of the superficial fascia and its attachments suggest a mechanical role in supporting structures and resisting loads during movement. The fibrous septa anchors fascia to the skin, providing stability and resistance against external forces, as well as protecting the nerves and blood vessels that pass towards the skin. Existing fascial bursae probably assist in decreasing pressure and facilitating freedom of movement adjacent to bony prominences. Elasticity and connectivity of the superficial fascia may explain the various responses to multidirectional loading. Furthermore, the presence of free nerve endings and mechanoreceptors within the fascia suggests that it may contribute to proprioception of the hindlimb, enhancing the awareness of body movement.

Skin Structure, Physiology, and Pathology in Topical and Transdermal Drug Delivery

Several industries are increasingly focused on enhancing the delivery of active ingredients through the skin to optimize therapeutic outcomes. By facilitating the penetration of active ingredients through the skin barrier, these enhancers can significantly improve the efficacy of various formulations, ranging from skincare products to therapeutic agents targeting systemic circulation. As the understanding of skin physiology and the mechanisms of drug absorption deepen, these industries are adopting permeation enhancers more widely, ultimately leading to better patient outcomes and expanded treatment options. However, the structure and physiological function of the skin can vary according to different factors, such as the area of the body and between individuals. These variations, along with external environmental exposures, aging and pathological conditions, introduce complexities that must be carefully considered when designing effective delivery systems. Considering the intricacies of skin structure and physiology, tailoring systems to account for regional differences, individual variability, and changes induced by environmental factors or disease is critical to optimizing therapeutic outcomes. This review discusses the features of skin structure, physiology, and pathologies, as well as the application of permeation enhancers in these contexts. Furthermore, it addresses the use of animal skin models in transdermal delivery and dermatological studies, along with the latest developments in this field.

Spiny mice are primed but fail to regenerate volumetric skeletal muscle loss injuries

BACKGROUND

In recent years, the African spiny mouse Acomys cahirinus has been shown to regenerate a remarkable array of severe internal and external injuries in the absence of a fibrotic response, including the ability to regenerate full-thickness skin excisions, ear punches, severe kidney injuries, and complete transection of the spinal cord. While skeletal muscle is highly regenerative in adult mammals, Acomys displays superior muscle regeneration properties compared with standard laboratory mice following several injuries, including serial cardiotoxin injections of skeletal muscle and volumetric muscle loss (VML) of the panniculus carnosus muscle following full-thickness excision injuries. VML is an extreme muscle injury defined as the irrecoverable ablation of muscle mass, most commonly resulting from combat injuries or surgical debridement. Barriers to the treatment of VML injury include early and prolonged inflammatory responses that promote fibrotic repair and the loss of structural and mechanical cues that promote muscle regeneration. While the regeneration of the panniculus carnosus in Acomys is impressive, its direct relevance to the study of VML in patients is less clear as this muscle has largely been lost in humans, and, while striated, is not a true skeletal muscle. We therefore sought to test the ability of Acomys to regenerate a skeletal muscle more commonly used in VML injury models.

METHODS

We performed two different VML injuries of the Acomys tibialis anterior muscle and compared the regenerative response to a standard laboratory mouse strain, Mus C57BL6/J.

RESULTS

Neither Acomys nor Mus recovered lost muscle mass or myofiber number within three months following VML injury, and Acomys also failed to recover force production better than Mus. In contrast, Acomys continued to express eMHC within the injured area even three months following injury, whereas Mus ceased expressing eMHC less than one-month post-injury, suggesting that Acomys muscle was primed, but failed, to regenerate.

CONCLUSIONS

While the panniculus carnosus muscle in Acomys regenerates following VML injury in the context of full-thickness skin excision, this regenerative ability does not translate to regenerative repair of a skeletal muscle.

Development and characterization of contraction-suppressed full-thickness skin wound model in rabbits

The wound healing process in rodents (rats and mice) and lagomorphs (rabbits) predominantly relies on wound contraction rather than re-epithelialization and granulation tissue formation. As a result, existing laboratory animal models for wound healing often fail to mimic human wound healing mechanisms accurately. This study introduces a standardized rabbit model with superior translational potential for skin wound healing research. Two full-thickness dermal wounds were created on the posterior dorsal surface of each rabbit using a standard 2 ×2 cm² template. One of these wounds was randomly selected to be treated as a contraction-suppressed wound by applying a transparent adhesive elastic bandage. At the same time, the other was retained as a standard full-thickness wound. Wound contraction was measured on 7, 14, 21, 28, and 35 days. Histomorphological evaluation was done on day 35 to evaluate the quality of wound healing. The findings indicate that transparent adhesive elastic bandage prolonged the wound healing time and suppressed wound contraction in rabbits. In addition, the healed contraction-suppressed full-thickness wounds had denser and thicker collagen fibers than the healed standard full-thickness wounds, indicating better collagen fiber deposition. Our model achieved a 100 % success rate in maintaining the transparent adhesive elastic bandage in the rabbits. Therefore, we have developed a simple, non-invasive, cost-effective method for preventing wound contraction. Further studies are required to establish the utility of this model for studying wound healing mechanisms and evaluating therapeutic interventions.

An Experimental Murine Model to Study Lipoatrophia Semicircularis

Lipoatrophia semicircularis is a benign pathology characterized by subcutaneous tissue atrophy that affects the skin and related structures. Its etiology remains unclear; however, in the recent few years, it has been proposed that electrostatic charges could be a potential factor. Based on this hypothesis, the aim of this work is to study the cause-effect relation between electrostatic energy and LS, providing insights into the molecular mechanisms. For this purpose, an experimental murine model was created using obese mice. One group served as a control and the other groups involved charging clothes with varying connections to the ground: through the skin, through the clothes or not connected to the ground). Skin biopsies showed that the most significant lesions, including lipophagic granulomas with inflammatory infiltrate, were found in the first group (connected to the ground through the skin). Lipophagic reactions without an inflammatory infiltrate were observed in the other groups subjected to electrical discharges. In the control mice, no histological changes were observed. Oxidative processes were also measured in lower limbs tissue. Malondialdehyde levels significantly increased in the lower limbs after electrostatic discharges. However, the presence of ground through a wire attached to highly conductive clothes around the thigh significantly reduced the effect of electrostatic charges on lipid peroxidation. To our knowledge, this is the first study in which an experimental model has been used to reproduce LS induced by electrostatic energy, suggesting a cause-effect relationship between electrostatic charge and discharge with fat tissue lesion.

Evaluation of Bioprinted Autologous Cartilage Grafts in an Immunocompetent Rabbit Model

The gold standard of auricular reconstruction involves manual graft assembly from autologous costal cartilage. The intervention may require multiple surgical procedures and lead to donor-site morbidity, while the outcome is highly dependent on individual surgical skills. A tissue engineering approach provides the means to produce cartilage grafts of a defined shape from autologous chondrocytes. The use of autologous cells minimizes the risk of host immune response; however, factors such as biomaterial compatibility and in vitro maturation of the tissue-engineered (TE) cartilage may influence the engraftment and shape-stability of TE implants. Here, this work tests the biocompatibility of bioprinted autologous cartilage constructs in a rabbit model. The TE cartilage is produced by embedding autologous auricular chondrocytes into hyaluronan transglutaminase (HATG) based bioink, previously shown to support chondrogenesis in human auricular chondrocytes in vitro and in immunocompromised xenotransplantation models in vivo. A drastic softening and loss of cartilage markers, such as sulfated glycosaminoglycans (GAGs) and collagen type II are observed. Furthermore, fibrous encapsulation and partial degradation of the transplanted constructs are indicative of a strong host immune response to the autologous TE cartilage. The current study thus illustrates the crucial importance of immunocompetent autologous animal models for the evaluation of TE cartilage function and compatibility.

Phosphatidylserine accelerates wound healing and reduces necrosis in the rats: Growth factor activation

To examine the effect of topical phosphatidylserine (PS) on wound healing factors and tissue necrosis in in vivo models. Topical PS was applied to evaluate aspects of the wound healing process and growth factors production of vascular endothelial growth factors (VEGF) as well a necrosis reduction in the skin flap of rat models. Moreover, phenytoin (PHT) and cyclosporine A (CsA) were used topically as positive control treatments in wound and necrosis models, respectively. Immunohistochemistry (IHC) VEGF, transforming growth factor-β (TGF-β), fibroblast growth factor (FGF) and histopathology were analysed on the wounds of rats. In the necrosis assessment, necrotic areas were determined on photography taken from the back skin of rats. Results indicated that PS topically enhanced significantly (P < 0.05) numbers of fibroblasts and endothelium while inhibiting the neutrophils and macrophages during the 14 days of wound treatment. Moreover, higher values of collagen deposition and epithelialization scores as well as wound recovery percentage (near 80%) were determined significantly (P < 0.05) in the PS group compared with the control. IHC analysis determined that FGF and VEGF cytokine factors were elevated in the wound site by topical PS. Moreover, the necrotic area was significantly (P < 0.05) improved in the PS group. Our experiment indicated that wound improvement and flap survival values in PS treatments were superior to PHT and CsA control groups, respectively. In conclusion, these findings suggest the potential of PS application in the healing of wounds and control of necrosis development after surgery or skin injuries.

Descriptive Anatomy of the Porcine Ventral Abdominal Wall as a Basis for Training Ventral Hernia Repair Techniques

Background: In recent times there has been a surge in innovative techniques concerning complex abdominal wall surgery. The availability of simulation models for comprehensive training and skill set development remains limited. Methods: Cadaveric dissections of the porcine abdominal wall were conducted to assess the suitability of anesthetized porcine models for training in both minimally invasive and open surgical procedures. Results: The panniculus carnosus, a typical muscular layer in mammals, is the outermost layer covering the anterolateral abdominal wall. Beneath it, there are four main pairs of abdominal wall muscles, mirroring the human anatomy. The rectus abdominis muscle runs straight along the linea alba and is surrounded by the rectus sheath, which is formed by the fusion of the lateral abdominal wall muscles and differs along the different regions of abdominal wall. The orientation of the muscle fibers in the lateral abdominal wall muscles, i.e., musculus obliquus externus, internus and transversus, is comparable to human anatomy. Although the transition lines between their muscular and aponeurotic part differ to some extent. Relevant for the adoption of surgical techniques, the transversus abdominis muscle is well-developed and resembles a bell curve shape as it transitions from its muscular to aponeurotic part. Conclusion: Despite minor differences in abdominal wall anatomy between pigs and humans, the porcine model provides a high level of fidelity in terms of both anatomical features and the development of skill sets relevant to hernia surgery.

Skin muscle is the initial site of viral replication for arboviral bunyavirus infection

The first step in disease pathogenesis for arboviruses is the establishment of infection following vector transmission. For La Crosse virus (LACV), the leading cause of pediatric arboviral encephalitis in North America, and other orthobunyaviruses, the initial course of infection in the skin is not well understood. Using an intradermal (ID) model of LACV infection in mice, we find that the virus infects and replicates nearly exclusively within skin-associated muscle cells of the panniculus carnosus (PC) and not in epidermal or dermal cells like most other arbovirus families. LACV is widely myotropic, infecting distal muscle cells of the peritoneum and heart, with limited infection of draining lymph nodes. Surprisingly, muscle cells are resistant to virus-induced cell death, with long term low levels of virus release progressing through the Golgi apparatus. Thus, skin muscle may be a key cell type for the initial infection and spread of arboviral orthobunyaviruses.

Identification and characterization of a potentially novel dorsal cutaneous muscle in rodents

In the course of performing a detailed dissection of adult rat to map the cutaneous nerves of cervical, thoracic, and lumbar levels a small and unexpected structure was isolated. It appeared to be a cutaneous striated muscle and was observed in both male and female rats and in mice but absent from cats and humans. With the skin reflected laterally from midline, the muscle lies closely apposed to the lateral border of the Thoracic Trapezius (Spinotrapezius) muscle and is easily missed in standard gross dissections. Focussed prosections were performed to identify the origin, insertion, and course of gross innervation. Identification of each of these elements showed them to be distinct from the nearby Trapezius and Cutaneous Trunci (Cutaneous Maximus in mouse) muscles. The striated muscle nature of the structure was validated with whole-mount microscopy. Consulting a range of published rodent anatomical atlases and gross anatomical experts revealed no prior descriptions. This preliminary report is an opportunity for the anatomical and research communities to provide input to either confirm the novelty of this muscle or refer to prior published descriptions in rodents or other species while the muscle, its innervation, and function are further characterized. Presuming this muscle is indeed novel, the name "Cutaneous Scapularis muscle" is proposed in accord with general principles of the anatomical field.

Regeneration of Panniculus Carnosus Muscle in Fetal Mice Is Characterized by the Presence of Actin Cables

Mammalian skin, including human and mouse skin, does not regenerate completely after injury; it is repaired, leaving a scar. However, it is known that skin wounds up to a certain stage of embryonic development can regenerate. The mechanism behind the transition from regeneration to scar formation is not fully understood. Panniculus carnosus muscle (PCM) is present beneath the dermal fat layer and is a very important tissue for wound contraction. In rodents, PCM is present throughout the body. In humans, on the other hand, it disappears and becomes a shallow fascia on the trunk. Fetal cutaneous wounds, including PCM made until embryonic day 13 (E13), regenerate completely, but not beyond E14. We visualized the previously uncharacterized development of PCM in the fetus and investigated the temporal and spatial changes in PCM at different developmental stages, ranging from full regeneration to non-regeneration. Furthermore, we report that E13 epidermal closure occurs through actin cables, which are bundles of actomyosin formed at wound margins. The wound healing process of PCM suggests that actin cables may also be associated with PCM. Our findings reveal that PCM regenerates through a similar mechanism.

Development of an ex vivo porcine skin model for the preclinical evaluation of subcutaneously injected biomacromolecules

Subcutaneous administration is used to deliver systemically-acting biotherapeutics, e.g. antibodies, and locally-acting biomacromolecules, e.g. hyaluronic acid. However, few preclinical models are available to evaluate post-injection behaviour in the tissue microenvironment. In vivo animal studies are costly, time-consuming, and raise obvious ethical concerns. In vitro models are cost-efficient, high-throughput solutions, but cannot simulate complex skin structure and biological function. An ex vivo model (containing hypodermis) with an extended culture period that enabled longitudinal studies would be of great interest for both the pharmaceutical and cosmeceutical industries. We describe the development of one such ex vivo model, using viable full-thickness porcine skin. Structural integrity was evaluated using a histological scoring system: spongiosis and epidermal detachment were identified as discriminating parameters. Ki67 and Claudin-1 expression reported on epidermal cell proliferation and barrier function, respectively and their expression decreased as a function of incubation time. After optimization, the system was used to investigate the fate/impact of subcutaneously administered hyaluronic acid (HA) formulations. The results showed that HA was localized at the injection site and adjacent adipocytes were well preserved during 5 days' incubation and confirmed that the full-thickness ex vivo porcine skin model could provide a platform for preclinical evaluation of subcutaneously injected biomacromolecules.

One bout of endurance exercise does not change gene expression or proliferation in a C26 colon carcinoma in immunocompetent mice

PURPOSE

Exercise typically reduces tumour growth, proliferation and improves outcomes. Many of these effects require exercise to change gene expression within a tumour, but whether exercise  actually affects gene expression within a tumour has not been investigated yet. The aim of this study was, therefore, to find out whether one bout of endurance exercise alters gene expression and proliferation in a C26 carcinoma in immunocompetent mice.

METHODS

BALB/c were injected with C26 colon carcinoma cells. Once the tumours had formed, the mice either ran for 65 min with increasing intensity or rested before the tumour was dissected. The tumours were then analysed by RNA-Seq and stained for the proliferation marker KI67.

RESULTS

One bout of running for 65 min did not systematically change gene expression in C26 carcinomas of BALB/c mice when compared to BALB/c mice that were rested. However, when analysed for sex, the expression of 17, mostly skeletal muscle-related genes was higher in the samples of the female mice taken post-exercise. Further histological analysis showed that this signal likely comes from the presence of muscle fibres from the panniculus carnosus muscle inside the tumours. Also, we found no differences in the positivity for the proliferation marker KI67 in the control and exercise C26 carcinomas.

CONCLUSION

A bout of exercise did not systematically affect gene expression or proliferation in C26 carcinomas in immunocompetent BALB/c mice.

Skin Models Used to Define Mechanisms of Action of Sulfur Mustard

Sulfur mustard (SM) is a threat to both civilian and military populations. Human skin is highly sensitive to SM, causing delayed erythema, edema, and inflammatory cell infiltration, followed by the appearance of large fluid-filled blisters. Skin wound repair is prolonged following blistering, which can result in impaired barrier function. Key to understanding the action of SM in the skin is the development of animal models that have a pathophysiology comparable to humans such that quantitative assessments of therapeutic drugs efficacy can be assessed. Two animal models, hairless guinea pigs and swine, are preferred to evaluate dermal products because their skin is morphologically similar to human skin. In these animal models, SM induces degradation of epidermal and dermal tissues but does not induce overt blistering, only microblistering. Mechanisms of wound healing are distinct in these animal models. Whereas a guinea pig heals by contraction, swine skin, like humans, heals by re-epithelialization. Mice, rats, and rabbits are also used for SM mechanistic studies. However, healing is also mediated by contraction; moreover, only microblistering is observed. Improvements in animal models are essential for the development of therapeutics to mitigate toxicity resulting from dermal exposure to SM.

Tilapia Fish Skin Treatment of Third-Degree Skin Burns in Murine Model

This study explored the feasibility of using fish skin bandages as a therapeutic option for third-degree skin burns. Following the California wildfires, clinical observations of animals with third-degree skin burns demonstrated increased comfort levels and reduced pain when treated with tilapia fish skin. Despite the promises of this therapy, there are few studies explaining the healing mechanisms behind the application of tilapia fish skin. In this study, mice with third-degree burns were treated with either a hydrocolloid adhesive bandage (control) (n = 16) or fish skin (n = 16) 7 days post-burn. Mice were subjected to histologic, hematologic, molecular, and gross evaluation at days 7, 16, and 28 post-burn. The fish skin offered no benefit to overall wound closure compared to hydrocolloids. Additionally, we detected no difference between fish skin and control treatments in regard to hypermetabolism or hematologic values. However, the fish skin groups exhibited 2 times more vascularization and 2 times higher expression of antimicrobial defensin peptide in comparison to controls. Proteomic analysis of the fish skin revealed the presence of antimicrobial peptides. Collectively, these data suggest that fish skin can serve as an innovative and cost-effective therapeutic alternative for burn victims to facilitate vascularization and reduce bacterial infection.

Combining bioengineered human skin with bioprinted cartilage for ear reconstruction

Microtia is a congenital disorder that manifests as a malformation of the external ear leading to psychosocial problems in affected children. Here, we present a tissue-engineered treatment approach based on a bioprinted autologous auricular cartilage construct (EarCartilage) combined with a bioengineered human pigmented and prevascularized dermo-epidermal skin substitute (EarSkin) tested in immunocompromised rats. We confirmed that human-engineered blood capillaries of EarSkin connected to the recipient's vasculature within 1 week, enabling rapid blood perfusion and epidermal maturation. Bioengineered EarSkin displayed a stratified epidermis containing mature keratinocytes and melanocytes. The latter resided within the basal layer of the epidermis and efficiently restored the skin color. Further, in vivo tests demonstrated favorable mechanical stability of EarCartilage along with enhanced extracellular matrix deposition. In conclusion, EarCartilage combined with EarSkin represents a novel approach for the treatment of microtia with the potential to circumvent existing limitations and improve the aesthetic outcome of microtia reconstruction.

Matricellular Proteins in the Homeostasis, Regeneration, and Aging of Skin

Matricellular proteins are secreted extracellular proteins that bear no primary structural functions but play crucial roles in tissue remodeling during development, homeostasis, and aging. Despite their low expression after birth, matricellular proteins within skin compartments support the structural function of many extracellular matrix proteins, such as collagens. In this review, we summarize the function of matricellular proteins in skin stem cell niches that influence stem cells' fate and self-renewal ability. In the epidermal stem cell niche, fibulin 7 promotes epidermal stem cells' heterogeneity and fitness into old age, and the transforming growth factor-β-induced protein ig-h3 (TGFBI)-enhances epidermal stem cell growth and wound healing. In the hair follicle stem cell niche, matricellular proteins such as periostin, tenascin C, SPARC, fibulin 1, CCN2, and R-Spondin 2 and 3 modulate stem cell activity during the hair cycle and may stabilize arrector pili muscle attachment to the hair follicle during piloerections (goosebumps). In skin wound healing, matricellular proteins are upregulated, and their functions have been examined in various gain-and-loss-of-function studies. However, much remains unknown concerning whether these proteins modulate skin stem cell behavior, plasticity, or cell-cell communications during wound healing and aging, leaving a new avenue for future studies.

Comparative anatomy of the felid brachial plexus reflects differing hunting strategies between Pantherinae (snow leopard, Panthera uncia) and Felinae (domestic cat, Felis catus)

The brachial plexus, a network of ventral rami providing somatic sensory and motor innervation to the forelimb, is of particular importance in felids. Large-bodied pantherines require powerful rotatory and joint stabilizing forelimb muscles to maintain secure holds on large prey, while smaller-bodied felines are small prey specialists reliant on manual dexterity. Brachial plexus dissections of two snow leopards (Panthera uncia) and two domestic cats (Felis catus) revealed that generally the morphology of the brachial plexus is quite conserved. However, differences in the nerves supplying the shoulder and antebrachium may reflect differing prey capture strategies between the subfamilies. The brachial plexus of both species derives from ventral rami of C6-T1. In P. uncia, an extensive musculus (m.) subscapularis with multiple pennations is innervated by a larger number of nn. subscapulares, deriving from more spinal cord levels than in F. catus. C6 continues to become n. suprascapularis in both taxa; however, in F. catus, it also gives branches that join with C7, while in P. uncia, it is dedicated to musculi (mm.) supraspinatus, infraspinatus, and a small branch to cervical musculature. In F. catus, nervus (n.) medianus receives direct contributions from more ventral rami than P. uncia, possibly reflecting a greater reliance on manual dexterity in prey capture in the former. In addition to primary innervation by n. thoracodorsalis, m. latissimus dorsi is also innervated by n. thoracicus lateralis near the axilla in both taxa, suggesting that it may belong to a complex of proximal forelimb musculature along with mm. pectoralis profundus and cutaneus trunci.

Staphylococcus xylosus and Staphylococcus aureus as commensals and pathogens on murine skin

Skin ulcers, skin dermatitis and skin infections are common phenomena in colonies of laboratory mice and are often found at increased prevalence in certain immunocompromised strains. While in many cases these skin conditions are mild, in other cases they can be severe and lead to animal morbidity. Furthermore, the presence of skin infections and ulcerations can complicate the interpretation of experimental protocols, including those examining immune cell activation. Bacterial species in the genus Staphylococcus are the most common pathogens recovered from skin lesions in mice. In particular, Staphylococcus aureus and Staphylococcus xylosus have both been implicated as pathogens on murine skin. Staphylococcus aureus is a well-known pathogen of human skin, but S. xylosus skin infections in humans have not been described, indicating that there is a species-specific difference in the ability of S. xylosus to serve as a skin pathogen. The aim of this review is to summarize studies that link S. aureus and S. xylosus to skin infections of mice and to describe factors involved in their adherence to tissue and their virulence. We discuss potential differences in mouse and human skin that might underlie the ability of S. xylosus to act as a pathogen on murine skin, but not human skin. Finally, we also describe mouse mutants that have shown increased susceptibility to skin infections with staphylococcal bacteria. These mutants point to pathways that are important in the control of commensal staphylococcal bacteria. The information here may be useful to researchers who are working with mouse strains that are prone to skin infections with staphylococcal bacteria.

Sternalis Syndrome Misidentified by Multiple Specialties Responding to Botox Treatment: A Case Report and Literature Review

When a clinician, especially one who is specialized in primary care is faced with presenting complaints of deep, sharp, anterior chest pain, the most common differential diagnoses include cardiac and gastrointestinal pain. Musculoskeletal pain is thought of less frequently as a possible root cause. In this case report, we describe the clinical journey of a female athlete who presented with complaints of burning anterior chest pain. Her sternalis syndrome pain was first misdiagnosed as pain of cardiac origin, resulting in pacemaker placement into the patient's chest. The pain continued, and the same musculoskeletal pain was then presumed to be of gastrointestinal origin due to a previous history of gastroesophageal reflux disease (GERD). As a result of this misidentification, the patient underwent an unnecessary esophageal surgical procedure. Here, we identify the origins of sternalis syndrome pain, what other conditions the pain may be confused with, and how clinicians should not be quick to exclude musculoskeletal pain from a differential diagnosis of acute chest pain. We discuss effective treatments for sternalis syndrome and shed light on this less common cause of anterior chest pain to promote more accurate diagnosis and avoidance of unnecessary surgical interventions.

LC-MS/MS quantitation of elastin crosslinker desmosines and histological analysis of skin aging characteristics in mice

Elastic fibers consist of an insoluble inner core of elastin, which confers elasticity and resilience to vertebral organs and tissues. Desmosine (DES) and isodesmosine (IDES) are potential biomarkers of pathologies that lead to decreased elastin turnover. Mice are commonly used in research to mimic humans because of their similar genetics, physiology, and organ systems. The present study thus used senescent accelerated prone (SAMP10) and senescent accelerated resistant (SAMR1) mice to examine the connection between aging and histological or biomolecular changes. Mice were divided into three groups: SAMP10 fed a control diet (CD), SAMP10 fed a high-fat diet (HFD), and SAMR1 fed a CD. The percent liver to total body weight ratio (%LW/BW), desmosines (DESs or DES/IDES) content, and histological alterations in skin samples were evaluated. DESs were quantified using an isotope-dilution liquid chromatography-tandem mass spectrometry method with isodesmosine-¹³C₃,¹⁵N₁ as the internal standard (ISTD). The assays were repeatable, reproducible, and accurate, with %CV values ≤ (1.90, 1.77, and 3.03), ISTD area %RSD of (1.54, 0.92, and 1.13), and %AC of (99.02 ± 1.86, 101.00 ± 2.30, and 101.30 ± 2.90) for the calibrations (equimolar DES/IDES, DES, and IDES, respectively). The average DESs content per dry-weight abdominal skin and %LW/BW were similar between the three groups. Histological analyses revealed elastin fibers in five randomly selected samples. The epidermis and dermal white adipose tissue layers were thicker in SAMP10 mice than SAMR1 mice. Thus, characteristic signs of aging in SAMP10 and SAMR1 mice could not be differentiated based on measurement of DESs content of the skin or %LW/BW, but aging could be differentiated based on microscopic analysis of histological changes in the skin components of SAMP10 and SAMR1 mice.

Chronic Wound Healing Models

In this paper, we review and analyze the commonly available wound healing models reported in the literature and discuss their advantages and issues, considering their relevance and translational potential to humans. Our analysis includes different in vitro and in silico as well as in vivo models and experimental techniques. We further explore the new technologies in the study of wound healing to provide an all encompassing review of the most efficient ways to proceed with wound healing experiments. We revealed that there is not one model of wound healing that is superior and can give translatable results to human research. Rather, there are many different models that have specific uses for studying certain processes or stages of wound healing. Our analysis suggests that when performing an experiment to assess stages of wound healing or different therapies to enhance healing, one must consider not only the species that will be used but also the type of model and how this can best replicate the physiology or pathophysiology in humans.

Human In Vitro Skin Models for Wound Healing and Wound Healing Disorders

Skin wound healing is essential to health and survival. Consequently, high amounts of research effort have been put into investigating the cellular and molecular components involved in the wound healing process. The use of animal experiments has contributed greatly to the knowledge of wound healing, skin diseases, and the exploration of treatment options. However, in addition to ethical concerns, anatomical and physiological inter-species differences often influence the translatability of animal-based studies. Human in vitro skin models, which include essential cellular and structural components for wound healing analyses, would improve the translatability of results and reduce animal experiments during the preclinical evaluation of novel therapy approaches. In this review, we summarize in vitro approaches, which are used to study wound healing as well as wound healing-pathologies such as chronic wounds, keloids, and hypertrophic scars in a human setting.

An Updated Review of Hypertrophic Scarring

Hypertrophic scarring (HTS) is an aberrant form of wound healing that is associated with excessive deposition of extracellular matrix and connective tissue at the site of injury. In this review article, we provide an overview of normal (acute) wound healing phases (hemostasis, inflammation, proliferation, and remodeling). We next discuss the dysregulated and/or impaired mechanisms in wound healing phases that are associated with HTS development. We next discuss the animal models of HTS and their limitations, and review the current and emerging treatments of HTS.

Atavistic and vestigial anatomical structures in the head, neck, and spine: an overview

Organisms may retain nonfunctional anatomical features as a consequence of evolutionary natural selection. Resultant atavistic and vestigial anatomical structures have long been a source of perplexity. Atavism is when an ancestral trait reappears after loss through an evolutionary change in previous generations, whereas vestigial structures are remnants that are largely or entirely functionless relative to their original roles. While physicians are cognizant of their existence, atavistic and vestigial structures are rarely emphasized in anatomical curricula and can, therefore, be puzzling when discovered incidentally. In addition, the literature is replete with examples of the terms atavistic and vestigial being used interchangeably without careful distinction between them. We provide an overview of important atavistic and vestigial structures in the head, neck, and spine that can serve as a reference for anatomists and clinical neuroscientists. We review the literature on atavistic and vestigial anatomical structures of the head, neck, and spine that may be encountered in clinical practice. We define atavistic and vestigial structures and employ these definitions consistently when classifying anatomical structures. Pertinent anatomical structures are numerous and include human tails, plica semilunaris, the vomeronasal organ, levator claviculae, and external ear muscles, to name a few. Atavistic and vestigial structures are found throughout the head, neck, and spine. Some, such as human tails and branchial cysts may be clinically symptomatic. Literature reports indicate that their prevalence varies across populations. Knowledge of atavistic and vestigial anatomical structures can inform diagnoses, prevent misrecognition of variation for pathology, and guide clinical interventions.

Skin Ageing: A Progressive, Multi-Factorial Condition Demanding an Integrated, Multilayer-Targeted Remedy

Of the human organs, skin is the most visible one that displays the manifestations of ageing. It has a very intricate microanatomical structure and performs several key physiological functions. The pathophysiology of cutaneous ageing is characterized by deterioration of structural stability and functional integrity, implying a continuous reduction in maximal function and reserve capacity, as a result of the accumulating damage due to both intrinsic and extrinsic factors. Elimination of unfavorable expressions associated with facial and cutaneous ageing is the key patient demand in aesthetic dermatology. Even though the progress has been made in nonsurgical therapies like fillers and lasers, non-invasive interventions by using skin care products designed for rejuvenation at an early stage are the most popular and accessible solution among people. In this review, we have scrutinized the ageing-associated cutaneous changes at molecular, cellular and tissue levels. To optimize the ageing process towards a healthy skin, we propose an integrated, multilayer-targeted intervention, which involves both topical application of anti-ageing formulations from outside and oral supplementation from inside. Additionally, several promising naturally derived ingredients are reviewed from an anti-aging perspective. Most of them possess various bioactivities and may contribute to the development of the mentioned anti-ageing remedy.

Examination of epigenetic inhibitor zebularine in treatment of skin wounds in healthy and diabetic mice

DNA methyltransferase inhibitor zebularine was proven to induce regeneration in the ear pinna in mice. We utilized a dorsal skin wound model to further evaluate this epigenetic inhibitor in wound healing. Full-thickness excisional wounds were made on the dorsum of 2 and 10-month-old healthy BALB/c and 3 and 8-month-old diabetic (db/db) mice, followed by topical or intraperitoneal zebularine delivery. Depending on the strain, age, dose, and delivery, the zebularine treatments either had no effect or accelerated or delayed wound closure. In principle, zebularine applied topically moderately promoted wound closure in the healthy but markedly delayed in the diabetic mice, which was in line with decreased viability of cultured keratinocytes from diabetic patients exposed to zebularine. The histological analysis revealed an improvement in the architecture of restored skin in zebularine-treated mice, manifested as a distinct layered pattern resembling panniculus carnosus. The finding corresponds with the zebularine-mediated activation of the Wnt5a gene, an essential regulator of Wnt signaling, the pathway involved in hair follicle development, the process which in turn is connected with regenerative skin healing. Although zebularine did not remarkably accelerate wound healing, zebularine and other epigenetic inhibitors deserve further testing as potential drugs to improve the quality of restored skin.

Metallated phthalocyanines and their hydrophilic derivatives for multi-targeted oncological photodynamic therapy

BACKGROUND AND AIM

A photosensitizer (PS) delivery and comprehensive tumor targeting platform was developed that is centered on the photosensitization of key pharmacological targets in solid tumors (cancer cells, tumor vascular endothelium, and cellular and non-cellular components of the tumor microenvironment) before photodynamic therapy (PDT). Interstitially targeted liposomes (ITLs) encapsulating zinc phthalocyanine (ZnPC) and aluminum phthalocyanine (AlPC) were formulated for passive targeting of the tumor microenvironment. In previous work it was established that the PEGylated ITLs were taken up by cultured cholangiocarcinoma cells. The aim of this study was to verify previous results in cancer cells and to determine whether the ITLs can also be used to photosensitize cells in the tumor microenvironment and vasculature. Following positive results, rudimentary in vitro and in vivo experiments were performed with ZnPC-ITLs and AlPC-ITLs as well as their water-soluble tetrasulfonated derivatives (ZnPCS4 and AlPCS4) to assemble a research dossier and bring this platform closer to clinical transition.

METHODS

Flow cytometry and confocal microscopy were employed to determine ITL uptake and PS distribution in cholangiocarcinoma (SK-ChA-1) cells, endothelial cells (HUVECs), fibroblasts (NIH-3T3), and macrophages (RAW 264.7). Uptake of ITLs by endothelial cells was verified under flow conditions in a flow chamber. Dark toxicity and PDT efficacy were determined by cell viability assays, while the mode of cell death and cell cycle arrest were assayed by flow cytometry. In vivo systemic toxicity was assessed in zebrafish and chicken embryos, whereas skin phototoxicity was determined in BALB/c nude mice. A PDT efficacy pilot was conducted in BALB/c nude mice bearing human triple-negative breast cancer (MDA-MB-231) xenografts.

RESULTS

The key findings were that (1) photodynamically active PSs (i.e., all except ZnPCS4) were able to effectively photosensitize cancer cells and non-cancerous cells; (2) following PDT, photodynamically active PSs were highly toxic-to-potent as per anti-cancer compound classification; (3) the photodynamically active PSs did not elicit notable systemic toxicity in zebrafish and chicken embryos; (4) ITL-delivered ZnPC and ZnPCS4 were associated with skin phototoxicity, while the aluminum-containing PSs did not exert detectable skin phototoxicity; and (5) ITL-delivered ZnPC and AlPC were equally effective in their tumor-killing capacity in human tumor breast cancer xenografts and superior to other non-phthalocyanine PSs when appraised on a per mole administered dose basis.

CONCLUSIONS

AlPC(S4) are the safest and most effective PSs to integrate into the comprehensive tumor targeting and PS delivery platform. Pending further in vivo validation, these third-generation PSs may be used for multi-compartmental tumor photosensitization.

Effect of All-trans Retinoic Acid on Panniculus Carnosus Muscle Regeneration in Fetal Mouse Wound Healing

The dermal panniculus carnosus (PC) muscle is critical for wound contraction in lower mammals and is a useful model of muscle regeneration owing to its high cellular metabolic turnover. During wound healing in mice, skin structures, including PC, are completely regenerated up to embryonic day (E) 13, but PC is only partially regenerated in fetuses or adult animals after E14. Nevertheless, the mechanisms underlying wound repair for complete regeneration in PC have not been fully elucidated. We hypothesized that retinoic acid (RA) signaling, which is involved in muscle differentiation, regulates PC regeneration.

Methods

Surgical injury was induced in ICR mice on E13 and E14. RA receptor alpha (RARα) expression in tissue samples from embryos was evaluated using immunohistochemistry and reverse transcription-quantitative polymerase chain reaction. To evaluate the effects of RA on PC regeneration, beads soaked in all-trans RA (ATRA) were implanted in E13 wounds, and tissues were observed. The effects of RA on myoblast migration were evaluated using a cell migration assay.

Results

During wound healing, RARα expression was enhanced at the cut surface in PCs of E13 wounds but was attenuated at the cut edge of E14 PCs. Implantation of ATRA-containing beads inhibited PC regeneration on E13 in a concentration-dependent manner. Treatment of myoblasts with ATRA inhibited cell migration.

Conclusions

ATRA inhibits PC regeneration, and decreased RARα expression in wounds after E14 inhibits myoblast migration. Our findings may contribute to the development of therapies to promote complete wound regeneration, even in the muscle.

VEGF-A and FGF4 Engineered C2C12 Myoblasts and Angiogenesis in the Chick Chorioallantoic Membrane

Angiogenesis is the formation of new blood vessels from pre-existing vessels. Adequate oxygen transport and waste removal are necessary for tissue homeostasis. Restrictions in blood supply can lead to ischaemia which can contribute to disease pathology. Vascular endothelial growth factor (VEGF) is essential in angiogenesis and myogenesis, making it an ideal candidate for angiogenic and myogenic stimulation in muscle. We established C2C12 mouse myoblast cell lines which stably express elevated levels of (i) human VEGF-A and (ii) dual human FGF4-VEGF-A. Both stably transfected cells secreted increased amounts of human VEGF-A compared to non-transfected cells, with the latter greater than the former. In vitro, conditioned media from engineered cells resulted in a significant increase in endothelial cell proliferation, migration, and tube formation. In vivo, this conditioned media produced a 1.5-fold increase in angiogenesis in the chick chorioallantoic membrane (CAM) assay. Delivery of the engineered myoblasts on Matrigel demonstrated continued biological activity by eliciting an almost 2-fold increase in angiogenic response when applied directly to the CAM assay. These studies qualify the use of genetically modified myoblasts in therapeutic angiogenesis for the treatment of muscle diseases associated with vascular defects.

Anatomical differences in the abdominal wall between animal species with implications for the transversus abdominis plane block: a systematic review

PURPOSE

With the increased use of simulation-based training using animal models for the education of surgical and anaesthetic techniques, an increased understanding of the anatomy of such models and how they compare to humans is required. The transversus abdominis plane block is a regional anaesthetic technique that requires an understanding of the abdominal wall anatomy along with proficient ultrasound use. The current review aims to compare the anatomy of the abdominal wall across species, particularly focussing on the pertinent differences within the class of mammals, and secondarily, it aims to address the implications of these differences for the use of simulation-based training of the transversus abdominis plane block.

METHODS

To achieve this, the PubMed, Web of Science and Google Scholar databases were searched for relevant literature. Studies pertaining to the musculature, vasculature or innervation of the anterolateral abdominal wall across species were included.

RESULTS

The mammalian abdominal wall differs in its musculature, vasculature or innervation from that of amphibians, birds or reptiles; however, among species of mammals, the structure of the abdominal wall follows a similar framework. Particular differences among mammals include the additional muscular layer of the panniculus carnosus found in most mammals other than humans, the variable arterial origins and dominant vascular supply of the abdominal wall and the number of thoracolumbar nerves innervating the abdominal wall.

CONCLUSION

When using animal models for simulation-based training, the pig is recommended for the transversus abdominis plane block given its closely homologous abdominal wall structure, availability and larger comparative size.

Advantages and Disadvantages of Using Small and Large Animals in Burn Research: Proceedings of the 2021 Research Special Interest Group

Multiple animal species and approaches have been used for modeling different aspects of burn care, with some strategies considered more appropriate or translatable than others. On April 15, 2021, the Research Special Interest Group of the American Burn Association held a virtual session as part of the agenda for the annual meeting. The session was set up as a pro/con debate on the use of small versus large animals for application to four important aspects of burn pathophysiology: burn healing/conversion; scarring; inhalation injury; and sepsis. For each of these topics, 2 experienced investigators (one each for small and large animal models) described the advantages and disadvantages of using these preclinical models. The use of swine as a large animal model was a common theme due to anatomic similarities with human skin. The exception to this was a well-defined ovine model of inhalation injury; both of these species have larger airways which allow for incorporation of clinical tools such as bronchoscopes. However, these models are expensive and demanding from labor and resource standpoints. Various strategies have been implemented to make the more inexpensive rodent models appropriate for answering specific questions of interest in burns. Moreover, modelling burn-sepsis in large animals has proven difficult. It was agreed that the use of both small and large animal models have merit for answering basic questions about the responses to burn injury. Expert opinion and the ensuing lively conversations are summarized herein, which we hope will help inform experimental design of future research.

Disrupting mechanotransduction decreases fibrosis and contracture in split-thickness skin grafting

Burns and other traumatic injuries represent a substantial biomedical burden. The current standard of care for deep injuries is autologous split-thickness skin grafting (STSG), which frequently results in contractures, abnormal pigmentation, and loss of biomechanical function. Currently, there are no effective therapies that can prevent fibrosis and contracture after STSG. Here, we have developed a clinically relevant porcine model of STSG and comprehensively characterized porcine cell populations involved in healing with single-cell resolution. We identified an up-regulation of proinflammatory and mechanotransduction signaling pathways in standard STSGs. Blocking mechanotransduction with a small-molecule focal adhesion kinase (FAK) inhibitor promoted healing, reduced contracture, mitigated scar formation, restored collagen architecture, and ultimately improved graft biomechanical properties. Acute mechanotransduction blockade up-regulated myeloid CXCL10-mediated anti-inflammation with decreased CXCL14-mediated myeloid and fibroblast recruitment. At later time points, mechanical signaling shifted fibroblasts toward profibrotic differentiation fates, and disruption of mechanotransduction modulated mesenchymal fibroblast differentiation states to block those responses, instead driving fibroblasts toward proregenerative, adipogenic states similar to unwounded skin. We then confirmed these two diverging fibroblast transcriptional trajectories in human skin, human scar, and a three-dimensional organotypic model of human skin. Together, pharmacological blockade of mechanotransduction markedly improved large animal healing after STSG by promoting both early, anti-inflammatory and late, regenerative transcriptional programs, resulting in healed tissue similar to unwounded skin. FAK inhibition could therefore supplement the current standard of care for traumatic and burn injuries.

Atavistic muscles in human anatomy: Evolutionary origins and clinical implications

The evolution and variations of human anatomy are of great interest to physicians and anatomists. Variations can be categorized as vestigial, accessory or atavistic structures. Vestigial muscles are frequently encountered structures that are normally present but have become rudimentary through evolution. Muscles that disappeared during evolution sometimes arise again, although rarely; such muscles are referred to as atavistic. They arise from failure of suppression of genetic loci. Some common atavistic muscles seen clinically are the extensor digitorum brevis manus, chondroepitrochlearis and plantaris. Atavistic muscles appear more frequently in the upper limb than in any other region of the human body. One explanation for the appearance of these muscles, mainly within the upper limbs, is based on the evolution of the complex upper extremities formed in humans today. Often, the presence of atavistic muscles is asymptomatic, but they can compromise the function of normal anatomical structures and complicate clinical situations if their presence is unknown. They can cause complications if they are confused with soft tissue pathology, if they compress or displace surrounding structures, or if they require an additional blood supply during times of exercise and stress. The purpose of this paper was to describe the common atavistic muscles, their hypothesized evolutionary origins, their potential complications and possible treatments for the diagnosing clinician.

A Systematic Review Comparing Animal and Human Scarring Models

Introduction

A reproducible, standardised model for cutaneous scar tissue to assess therapeutics is crucial to the progress of the field. A systematic review was performed to critically evaluate scarring models in both animal and human research.

Method

All studies in which cutaneous scars are modelling in animals or humans were included. Models that were focused on the wound healing process or those in humans with scars from an existing injury were excluded. Ovid Medline^® was searched on 25 February 2019 to perform two near identical searches; one aimed at animals and the other aimed at humans. Two reviewers independently screened the titles and abstracts for study selection. Full texts of potentially suitable studies were then obtained for analysis.

Results

The animal kingdom search yielded 818 results, of which 71 were included in the review. Animals utilised included rabbits, mice, pigs, dogs and primates. Methods used for creating scar tissue included sharp excision, dermatome injury, thermal injury and injection of fibrotic substances. The search for scar assessment in humans yielded 287 results, of which 9 met the inclusion criteria. In all human studies, sharp incision was used to create scar tissue. Some studies focused on patients before or after elective surgery, including bilateral breast reduction, knee replacement or midline sternotomy.

Discussion

The rabbit ear scar model was the most popular tool for scar research, although pigs produce scar tissue which most closely resembles that of humans. Immunodeficient mouse models allow for in vivo engraftment and study of human scar tissue, however, there are limitations relating to the systemic response to these xenografts. Factors that determine the use of animals include cost of housing requirements, genetic traceability, and ethical concerns. In humans, surgical patients are often studied for scarring responses and outcomes, but reproducibility and patient factors that impact healing can limit interpretation. Human tissue use in vitro may serve as a good basis to rapidly screen and assess treatments prior to clinical use, with the advantage of reduced cost and setup requirements.

Altered regulation of mesenchymal cell senescence in adipose tissue promotes pathological changes associated with diabetic wound healing

Pathologic diabetic wound healing is caused by sequential and progressive deterioration of hemostasis, inflammation, proliferation, and resolution/remodeling. Cellular senescence promotes wound healing; however, diabetic wounds exhibit low levels of senescent factors and accumulate senescent cells, which impair the healing process. Here we show that the number of p15^INK4B + PDGFRα + senescent mesenchymal cells in adipose tissue increases transiently during early phases of wound healing in both non-diabetic mice and humans. Transplantation of adipose tissue from diabetic mice into non-diabetic mice results in impaired wound healing and an altered cellular senescence–associated secretory phenotype (SASP), suggesting that insufficient induction of adipose tissue senescence after injury is a pathological mechanism of diabetic wound healing. These results provide insight into how regulation of senescence in adipose tissue contributes to wound healing and could constitute a basis for developing therapeutic treatment for wound healing impairment in diabetes.

Type-2 diabetic adipose tissue impairs transient senescence during wound healing with expression of different components of the senescence-associated secretory phenotype (SASP), and this is associated with deteriorated wound healing.

Calculating and comparing codon usage values in rare disease genes highlights codon clustering with disease-and tissue- specific hierarchy

We designed a novel strategy to define codon usage bias (CUB) in 6 specific small cohorts of human genes. We calculated codon usage (CU) values in 29 non-disease-causing (NDC) and 31 disease-causing (DC) human genes which are highly expressed in 3 distinct tissues, kidney, muscle, and skin. We applied our strategy to the same selected genes annotated in 15 mammalian species. We obtained CUB hierarchical clusters for each gene cohort which showed tissue-specific and disease-specific CUB fingerprints. We showed that DC genes (especially those expressed in muscle) display a low CUB, well recognizable in codon hierarchical clustering. We defined the extremely biased codons as "zero codons" and found that their number is significantly higher in all DC genes, all tissues, and that this trend is conserved across mammals. Based on this calculation in different gene cohorts, we identified 5 codons which are more differentially used across genes and mammals, underlining that some genes have favorite synonymous codons in use. Since of the muscle genes clear clusters, and, among these, dystrophin gene surprisingly does not show any "zero codon" we adopted a novel approach to study CUB, we called "mapping-on-codons". We positioned 2828 dystrophin missense and nonsense pathogenic variations on their respective codon, highlighting that its frequency and occurrence is not dependent on the CU values. We conclude our strategy consents to identify a hierarchical clustering of CU values in a gene cohort-specific fingerprints, with recognizable trend across mammals. In DC muscle genes also a disease-related fingerprint can be observed, allowing discrimination between DC and NDC genes. We propose that using our strategy which studies CU in specific gene cohorts, as rare disease genes, and tissue specific genes, may provide novel information about the CUB role in human and medical genetics, with implications on synonymous variations interpretation and codon optimization algorithms.

The panniculus carnosus muscle: a missing link in the chronicity of heel pressure ulcers?

Chronic and recurring pressure ulcers (PUs) create an unmet need for predictive biomarkers. In this work, we examine the panniculus carnosus, a thin cutaneous muscle, traditionally considered vestigial in humans, and ask whether the panniculus may play a role in the chronicity and reinjury of heel PUs. To determine whether humans have a panniculus muscle layer at the heel, we dissected eight cadavers. To assess the influence of the panniculus layer on PU, we performed computational simulations of supine weight bearing. Finally, we assessed panniculus regeneration in fluorescent mice. Results show a panniculus layer present in all cadavers examined. Simulations show a thin layer of panniculus muscle causes a dramatic decrease in the volume of soft tissue experiencing high strain and stress, compared to a heel without a panniculus. Importantly, in the mouse model, the panniculus fails to regenerate after PU, even when other cutaneous layers had fully regenerated. Our work shows that the panniculus is able to redistribute load around the heel bone, which might allow it to prevent PUs. Moreover, it is highly susceptible to incomplete regeneration after PU. Poor panniculus regeneration after PU might be a predictive anatomical biomarker for recurrence, and this biomarker should be evaluated prospectively in future clinical trials.

The prevalence and distribution of sternalis muscle: a meta-analysis of published literature of the last two hundred years

The sternalis muscle (SM) is an anatomical variant that lies subcutaneously and is superficial to the pectoralis major muscle or sternum. The present meta-analysis was conducted to analyze the prevalence, anatomical features, and variance of the SM in different population. In total, 98 studies were included for this meta-analysis. Eighty-two studies dealt with adult subjects, and sixteen studies with fetuses. The worldwide prevalence of SM was observed to be 6% or 0.06 [0.05-0.7, 95% CI] in 27,470 adults, whereas it was 0.29 [0.20-0.39, 95% CI] in 673 fetuses. In 259 anencephalic fetuses, the prevalence was 44% or 0.44 [0.26-0.63, 95% CI], while the same in 414 fetuses without anencephaly was 16% or 0.16 [0.06-0.27, 95% CI]. The reported prevalence rate in Asian mongoloid population (9.1% = 0.091) was three times that of the Asian Caucasian population (3.33% = 0.0333). The prevalence in European descent was 3.93%. Interestingly, the reported prevalence rates in North and South American populations were 3.44% and 3.66%, almost being equivalent. The cadaveric investigations revealed that the SM had an overall prevalence of 5.96% in adults based on 76 studies, which was higher than other modalities of investigations. The multi-detector computerized tomography (MDCT) had shown the prevalence of approximately 4.33%. The same was reported in surgical studies and mammographic studies as 0.47% and 0.02%, respectively. The SM is not an unusual variant of the chest wall musculature. MDCT could be a new method to precisely demonstrate the morphology, course, and size of the SM in vivo.

Novel suction-based in vivo cutaneous DNA transfection platform

This work reports a suction-based cutaneous delivery method for in vivo DNA transfection. Following intradermal Mantoux injection of plasmid DNA in a rat model, a moderate negative pressure is applied to the injection site, a technique similar to Chinese báguàn and Middle Eastern hijama cupping therapies. Strong GFP expression was demonstrated with pEGFP-N1 plasmids where fluorescence was observed as early as 1 hour after dosing. Modeling indicates a strong correlation between focal strain/stress and expression patterns. The absence of visible and/or histological tissue injury contrasts with current in vivo transfection systems such as electroporation. Specific utility was demonstrated with a synthetic SARS-CoV-2 DNA vaccine, which generated host humoral immune response in rats with notable antibody production. This method enables an easy-to-use, cost-effective, and highly scalable platform for both laboratorial transfection needs and clinical applications for nucleic acid–based therapeutics and vaccines.

Skin adhesion to the percutaneous component of direct bone anchored systems: systematic review on preclinical approaches and biomaterials

Nowadays, direct bone anchored systems are an increasingly adopted approach in the therapeutic landscape for amputee patients. However, the percutaneous nature of these devices poses a major challenge to obtain a stable and lasting proper adhesion between the implant surface and the skin. A systematic review was carried out in three databases (PubMed, Scopus, Web of Science) to provide an overview of the innovative strategies tested with preclinical models (in vitro and in vivo) in the last ten years to improve the skin adhesion of direct bone anchored systems. Fifty five articles were selected after screening, also employing PECO question and inclusion criteria. A modified Cochrane RoB 2.0 tool for the in vitro studies and the SYRCLE tool for in in vivo studies were used to assess the risk of bias. The evidence collected suggests that the implementation of porous percutaneous structures could be one of the most favorable approach to improve proper skin adhesion, especially in association with bioactive coatings, as hydroxyapatite, and exploiting the field of nanostructure. Some issues still remain open as (a) the identification and characterization of the best material/coating association able to limit the shear stresses at the interface and (b) the role of keratinocyte turnover on the skin/biomaterial adhesion and integration processes.

Effects of Caffeine Consumption on Autologous Full-Thickness Skin Graft Healing in an Animal Model

Background There exists contradictory evidence that states both the beneficial and deleterious effects of caffeine on wound healing. The general population might unknowingly consume caffeine that negatively affects wound healing. The main objective of this study is to investigate the effect of daily caffeine consumption on wound healing, specifically full-thickness skin graft (FTSG).

Methods Forty Sprague–Dawley rats were randomized into four groups of equal size: control-dose (CD), low-dose (LD), medium-dose (MD), and high-dose (HD) caffeine groups. After autologous FTSG, all subjects in the intervention group were given daily pure caffeine gavage. The FTSG was explanted 7 days posttransplant. The graft viability, secondary contraction, and adherence were evaluated macroscopically, while fibroblast and collagen deposition was analyzed microscopically with hematoxylin eosin stain.

Results The least graft viability (72.8 ± 20.7%, clinical wound assessment scale [CWAS] 2.4), highest secondary contraction (11.4 ± 10.5%), and fibroblast count (331.8 ± 88.6 cells/5 high power fields) were observed in the MD group. More collagen synthesis was observed in subjects who consumed caffeine. The level of secondary contraction, fibroblast count as well as graft viability and collagen synthesis were positively correlated.

Conclusions Daily consumption of caffeine impairs graft viability when given in medium dose and increases collagen synthesis, irrespective of dosage. This study was in experimental rats; the results are not directly translatable to humans.

Disrupting biological sensors of force promotes tissue regeneration in large organisms

Tissue repair and healing remain among the most complicated processes that occur during postnatal life. Humans and other large organisms heal by forming fibrotic scar tissue with diminished function, while smaller organisms respond with scarless tissue regeneration and functional restoration. Well-established scaling principles reveal that organism size exponentially correlates with peak tissue forces during movement, and evolutionary responses have compensated by strengthening organ-level mechanical properties. How these adaptations may affect tissue injury has not been previously examined in large animals and humans. Here, we show that blocking mechanotransduction signaling through the focal adhesion kinase pathway in large animals significantly accelerates wound healing and enhances regeneration of skin with secondary structures such as hair follicles. In human cells, we demonstrate that mechanical forces shift fibroblasts toward pro-fibrotic phenotypes driven by ERK-YAP activation, leading to myofibroblast differentiation and excessive collagen production. Disruption of mechanical signaling specifically abrogates these responses and instead promotes regenerative fibroblast clusters characterized by AKT-EGR1.

Humans and other large mammals heal wounds by forming fibrotic scar tissue with diminished function. Here, the authors show that disrupting mechanotransduction through the focal adhesion kinase pathway in large animals accelerates healing, prevents fibrosis, and enhances skin regeneration.