Time-dependent appearance of myofibroblasts in granulation tissue of human skin wounds

Dating Skin Lesions of Forensic Interest by Immunohistochemistry and Immunofluorescence Techniques: A Scoping Literature Review

Wound age estimation is a significant issue in forensic pathology. Although various methods have been evaluated, no gold standard system or model has been proposed, and accurate injury time estimation is still challenging. The distinction between vital skin wounds-i.e., ante-mortem lesions-and skin alterations that occur after death is a crucial goal in forensic pathology. Once the vitality of the wound has been confirmed, the assessment of the post-trauma interval (PTI) is also fundamental in establishing the causal relationship between the traumatic event and death. The most frequently used techniques in research studies are biochemistry, molecular biology, and immunohistochemistry (IHC). Biochemical methods take advantage of the chemical and physical techniques. A systematic literature search of studies started on 18 February 2023. The search was conducted in the main databases for biomedical literature, i.e., PubMed and Scopus, for papers published between 1973 and 2022, focusing on different techniques of immunohistochemistry and immunofluorescence (IF) for estimating the PTI of skin wounds. The present study involves a comprehensive and structured analysis of the existing literature to provide a detailed and comprehensive overview of the different IHC techniques used to date skin lesions, synthesize the available evidence, critically evaluate the methodologies, and eventually draw meaningful conclusions about the reliability and effectiveness of the different markers that have been discovered and used in wound age estimation.

Immunohistochemical study of CD31 and α-SMA expression for age estimation of porcine skin wounds

Age estimation of wounds in veterinary forensic investigations is based on the presence and amount of granulation tissue. However, accurate age assessment is challenging and new time-dependent markers are warranted to support and improve the current procedure. The objective of this study was to evaluate the expression of CD31-positive blood vessels and α-smooth muscle action (α-SMA)-positive myofibroblasts in granulation tissue in order to evaluate their value as markers for porcine wound age estimation in a veterinary forensic context. Immunohistochemical expression of CD31 and α-SMA in 14 experimental porcine skin wounds of different ages (4, 6, 8, 10, 18, 27 and 35 days) and 11 forensic porcine wound specimens (of unknown age) were evaluated. CD31-positive blood vessels and α-SMA-positive myofibroblasts were present in the granulation tissue in the experimental wounds at all time points. A significant decrease in the mean blood vessel counts was found in wounds aged 18, 27 and 35 days compared with wounds aged 6 days (P < 0.001), when assessing both the superficial and deep part of the wound bed. α-SMA expression was lower at 27 and 35 days post wounding compared with 6-18 days post wounding. Combined assessment of three parameters (mean blood vessel counts in the superficial and deep wound beds and α-SMA expression) could approximately specify the age of the wounds as either 6-18 days or ≥27 days. In two of the forensic cases a combination of the three parameters yielded results that were similar to the experimental wounds, indicating a wound age of 6-18 days or ≥27 days, respectively. In the remaining forensic cases a combination of the three parameters did not show the same expression pattern as in the experimental wounds. The results indicate that in some forensic cases the application of CD31 and α-SMA markers appeared to support the current procedure for porcine wound age estimation, but this must be combined with pathological characteristics.

Extended characterization of IL-33/ST2 as a predictor for wound age determination in skin wound tissue samples of humans and mice

Interleukin (IL)-33, an important inflammatory cytokine, is highly expressed in skin wound tissue and serum of humans and mice, and plays an essential role in the process of skin wound healing (SWH) dependent on the IL-33/suppression of tumorigenicity 2 (ST2) pathway. However, whether IL-33 and ST2 themselves, as well as their interaction, can be applied for skin wound age determination in forensic practice remains incompletely characterized. Human skin samples with injured intervals of a few minutes to 24 hours (hs) and mouse skin samples with injured intervals of 1 h to 14 days (ds) were collected. Herein, the results demonstrated that IL-33 and ST2 are increased in the human skin wounds, and that in mice skin wounds, there is an increase over time, with IL-33 expression peaking at 24 hs and 10 ds, and ST2 expression peaking at 12 hs and 7 ds. Notably, the relative quantity of IL-33 and ST2 proteins < 0.35 suggested a wound age of 3 hs; their relative quantity > 1.0 suggested a wound age of 24 hs post-mouse skin wounds. In addition, immunofluorescent staining results showed that IL-33 and ST2 were consistently expressed in the cytoplasm of F4/80-positive macrophages and CD31-positive vascular endothelial cells with or without skin wounds, whereas nuclear localization of IL-33 was absent in α-SMA-positive myofibroblasts with skin wounds. Interestingly, IL-33 administration facilitated the wound area closure by increasing the proliferation of cytokeratin (K) 14 -positive keratinocytes and vimentin-positive fibroblasts. In contrast, treating with its antagonist (i.e., anti-IL-33) or receptor antagonist (e.g., anti-ST2) exacerbated the aforementioned pathological changes. Moreover, treatment with IL-33 combined with anti-IL-33 or anti-ST2 reversed the effect of IL-33 on facilitating skin wound closure, suggesting that IL-33 administration facilitated skin wound closure through the IL-33/ST2 signaling pathway. Collectively, these findings indicate that the detection of IL-33/ST2 might be a reliable biomarker for the determination of skin wound age in forensic practice.

The "hypopigmented" bitemark: a clinical and histologic appraisal

So-called "hypopigmented" bitemark patterns, commonly seen but not limited to dark skinned individuals, can be of value in forensic investigations. The process of aging bitemarks observed on skin is controversial and without guidelines. This report analyzes tissue obtained from the site of a hypopigmented bitemark using special histochemical stains for the identification of melanin pigment, and a panel of immunohistochemical markers to aid in the aging process. Histologic evaluation clearly showed that cellular changes in the hypopigmented area were indicative of wound healing that had taken place over a period of time. This validates the hypothesis that a hypopigmented bitemark is an indication of a wound inflicted some days previously. These findings have value in forensic investigations, particularly in cases of suspected long-term physical abuse.

Macrophage polarity and wound age determination

We investigated the dynamics of the gene expression of M1 and M2 macrophage markers during skin wound healing in mice. Expression of M1-macrophage markers, such as Il12a, Tnf, Il6, Il1b, and Nos2 was upregulated after wounding and peaked at 1 or 3 days after injury, and that of M2-macrophage markers such as Mrc1, Cd163, Ccl17, Arg, and Tgfb1, peaked at 6 days after injury. Consistent with these findings, using triple-color immunofluorescence analysis revealed that F4/80⁺CD80⁺ M1 macrophages were more abundant than F4/80⁺CD206⁺ M2 macrophages on day 3 in mouse wound specimens, and that M2 macrophages were prominently detected in day 6 wounds. For application in forensic practice, we examined macrophage polarization using human wound specimens. The average ratios of CD68⁺iNOS⁺ M1 macrophages to CD68⁺CD163⁺ M2 macrophages (M1/M2 ratios) were greater than 2.5 for the wounds aged 2-5 days. Out of 11 wounds aged 1-5 days, five samples had the M1/M2 ratios of > 3.0. These observations propose that the M1/M2 ratios of 3.0 would indicate a wound age of 1-5 days as the forensic opinion. This study showed that M1 and M2 macrophages in human skin wound might be a promising marker for wound age determination.

The pig as a model system for investigating the recruitment and contribution of myofibroblasts in skin healing

In the skin-healing field, porcine models are regarded as a useful analogue for human skin due to their numerous anatomical and physiological similarities. Despite the widespread use of porcine models in skin healing studies, the initial origin, recruitment and transition of fibroblasts to matrix-secreting contractile myofibroblasts are not well defined for this model. In this review, we discuss the merit of the pig as an animal for studying myofibroblast origin, as well as the challenges associated with assessing their contributions to skin healing. Although a variety of wound types (incisional, partial thickness, full thickness, burns) have been investigated in pigs in attempts to mimic diverse injuries in humans, direct comparison of human healing profiles with regards to myofibroblasts shows evident differences. Following injury in porcine models, which often employ juvenile animals, myofibroblasts are described in the developing granulation tissue at 4 days, peaking at Days 7-14, and persisting at 60 days post-wounding, although variations are evident depending on the specific pig breed. In human wounds, the presence of myofibroblasts is variable and does not correlate with the age of the wound or clinical contraction. Our comparison of porcine myofibroblast-mediated healing processes with those in humans suggests that further validation of the pig model is essential. Moreover, we identify several limitations evident in experimental design that need to be better controlled, and standardisation of methodologies would be beneficial for the comparison and interpretation of results. In particular, we discuss anatomical location of the wounds, their size and depth, as well as the healing microenvironment (wet vs. moist vs. dry) in pigs and how this could influence myofibroblast recruitment. In summary, although a widespread model used in the skin healing field, further research is required to validate pigs as a useful analogue for human healing with regards to myofibroblasts.

Extracellular Matrix and Dermal Fibroblast Function in the Healing Wound

Significance: Fibroblasts play a critical role in normal wound healing. Various extracellular matrix (ECM) components, including collagens, fibrin, fibronectin, proteoglycans, glycosaminoglycans, and matricellular proteins, can be considered potent protagonists of fibroblast survival, migration, and metabolism. Recent Advances: Advances in tissue culture, tissue engineering, and ex vivo models have made the examination and precise measurements of ECM components in wound healing possible. Likewise, the development of specific transgenic animal models has created the opportunity to characterize the role of various ECM molecules in healing wounds. In addition, the recent characterization of new ECM molecules, including matricellular proteins, dermatopontin, and FACIT collagens (Fibril-Associated Collagens with Interrupted Triple helices), further demonstrates our cursory knowledge of the ECM in coordinated wound healing. Critical Issues: The manipulation and augmentation of ECM components in the healing wound is emerging in patient care, as demonstrated by the use of acellular dermal matrices, tissue scaffolds, and wound dressings or topical products bearing ECM proteins such as collagen, hyaluronan (HA), or elastin. Once thought of as neutral structural proteins, these molecules are now known to directly influence many aspects of cellular wound healing. Future Directions: The role that ECM molecules, such as CCN2, osteopontin, and secreted protein, acidic and rich in cysteine, play in signaling homing of fibroblast progenitor cells to sites of injury invites future research as we continue investigating the heterotopic origin of certain populations of fibroblasts in a healing wound. Likewise, research into differently sized fragments of the same polymeric ECM molecule is warranted as we learn that fragments of molecules such as HA and tenascin-C can have opposing effects on dermal fibroblasts.

Detection of endothelial progenitor cells in human skin wounds and its application for wound age determination

Endothelial progenitor cells (EPCs), a newly identified cell type, are bone marrow-derived progenitor cells that co-express stem cell markers and vascular endothelial growth factor (VEGF) receptor (Flk-1). In this study, a double-color immunofluorescence analysis was carried out using anti-CD34 and anti-Flk-1 antibodies to examine the time-dependent appearance of EPCs, using 52 human skin wounds with different wound ages (Group I, 0-1 days; Group II, 2-6 days; Group III, 7-14 days; and Group IV, 17-21 days). In wound specimens with an age of less than one day, CD34(+)/Flk-1(+) EPCs were not detected. EPCs were initially observed in wounds aged two days, and their number was increased in lesions with advances in wound age. In morphometrical analysis, the average number of EPCs was the highest in the wounds of Group III. Especially, 20 out of 21 wounds aged 7-12 days had >20 EPCs, and all wound samples with postinfliction intervals of 14-21 days had <15 EPCs. These observations at least showed that >20 EPCs would indicate a wound age of 7-12 days. Taken together, our observations indicate the detection of EPCs would be useful for wound age determination.

Analysis of morphological characteristics and expression levels of extracellular matrix proteins in skin wounds to determine wound age in living subjects in forensic medicine

OBJECTIVE

Wound age determination in living subjects is important in routine diagnostics in forensic medicine. Macroscopical description of a wound to determine wound age however is inadequate. The aim of this study was to assess whether it would be feasible to determine wound age via analysis of morphological characteristics and extracellular matrix proteins in skin biopsies of living subjects referred to a forensic outpatient clinic.

METHODS

Skin biopsies (n=101), representing the border area of the wound, were taken from skin injuries of known wound age (range: 4.5h-25 days) in living subjects. All biopsies were analyzed for 3 morphological features (ulceration, parakeratosis and hemorrhage) and 3 extracellular matrix markers (collagen III, collagen IV and α-SMA). For quantification, biopsies were subdivided in 4 different timeframes: 0.2-2 days, 2-4 days, 4-10 days and 10-25 days old wounds. Subsequently, a probability scoring system was developed.

RESULTS

For hemorrhage, collagen III, collagen IV and α-SMA expression no relation with wound age was found. Ulceration was only found in wounds of 0.2-2, 2-4 and 4-10 days old, implying that the probability that a wound was more than 10 days old in case of ulceration is equal to 0%. Also parakeratosis was almost exclusively found in wounds of 0.2-2, 2-4 and 4-10 days old, except for one case with a wound age of 15 days old. The probability scoring system of all analyzed markers, as depicted above, however can be used to calculate individual wound age probabilities in biopsies of skin wounds of living subjects.

CONCLUSIONS

We have developed a probability scoring system, analysing morphological characteristics and extracellular matrix proteins in superficial skin biopsies of wounds in living subjects that can be applied in forensic medicine for wound age determination.

Fibronectin EIIIA splicing variant: A useful contribution to forensic wounding interval estimation

A fibronectin splicing variant, Fn containing an extra type III domain (EIIIA in rat, ED1 or EDA in human) has recently attracted more attention because of its sensitive response in injury of adult tissue. The characteristic that this form is absent in adult tissue while it is commonly expressed in fetal tissues and injured adult tissue is useful in estimation of injury interval in forensic science. The regulation of fibronectin splicing was studied by immunohistochemistry by using monoclonal antibody to EIIIA on sections from paraffin embedded rat skin sample after contusion. The results indicated that epidermic cells and hair follicle epithelium of rat skin were found positive staining at 6h after injury, and the color became darker with prolonged wounding time. Based on the above result, we invented a type of test paper assayed for EIIIA-Fn splicing variant by using immune colloidal gold technique. After dipping one end of test paper in the supernatant fluid of tissue homogenates of injury skin for few minutes, detecting line could be found. It showed that all experimental injured samples revealed positive staining; the darkness of positive staining was dependent on the injury time, while control normal skin cannot found positive staining. It is concluded that there is a close relationship between the expression of EIIIA-Fn splicing variant and wounding interval, and that the gold-labeled test paper can be useful in distinguishing ante- and post-mortem injury, and in estimation of wounding interval in forensic science.

Time-course changes in the expression of heme oxygenase-1 in human subcutaneous hemorrhage

To determine the time-course of human subcutaneous hemorrhage, heme oxygenase (HO)-1 expression and macrophage infiltration were observed using an immunohistochemical technique and semiquantitative analysis. The number of immunoreactive cells and the number of all infiltrating cells of each microscopic field were counted, and the ratio of the former to the latter was calculated as the positive cells ratio. An increase in the HO-1-positive cells ratio was observed starting at 3 h after injury, and the maximum ratio was observed 3 days after injury. The pattern of the increase in the macrophage ratio was similar to that of the HO-1-positive cells ratio in the early period after injury. Observation of serial sections revealed that the expression of HO-1 in the cells corresponded to the localization of macrophage. The present results suggest that the determination of HO-1 expression, as derived from macrophages, might be useful for the estimation of the time-course of subcutaneous hemorrhage.

Forensic application of VEGF expression to skin wound age determination

An immunohistochemical study combined with morphometry was carried out to examine the time-dependent expression of vascular endothelial growth factor (VEGF) using 53 human skin wounds with different wound ages (groups I: 0-12 h, II: 1-4 days, III: 7-14 days and IV: 17-21 days). In the human wound specimens aged 4-12 h, neutrophils recruited at the wound showed no positive signals for VEGF. With an increase in wound ages of > or =7 days, granulation tissue and angiogenesis were observed, with the migration of macrophages and fibroblasts of which the cytoplasm expressed VEGF-positive reactions. Morphometrically, the average VEGF-positive ratio was highest in group III, followed by that of group IV. In groups III and IV, 13 out of 26 wound samples had VEGF-positive ratios of more than 50%. However, all of the wound samples in groups I and II showed VEGF-positive ratios of less than 50%. With regard to the practical applicability and forensic validity, these observations suggest that a VEGF-positive ratio of more than 50% possibly indicates a wound age of 7 days or more.

Localization and regulation of pregnancy-associated plasma protein a expression in healing human skin

Pregnancy-associated plasma protein A (PAPP-A) is an IGF-binding protein-4 (IGFBP-4) metalloproteinase that cleaves inhibitory IGFBP-4 to amplify local IGF-I bioavailability in vitro. Thus it has functional implications in injury/repair responses. In this study we determined PAPP-A expression in healing human skin. Wounds were induced with a scalpel on the forearms of three normal subjects and were allowed to heal by first intention. Biopsies obtained on d 0, 2, 8, and 14 were processed for immunohistochemical detection of PAPP-A, IGF-I, and IGFBP-4. In uninjured skin (d 0), strong staining for PAPP-A was present in the epidermis, sweat and sebaceous gland epithelial cells, hair follicles, and blood vessels; no PAPP-A was detected in dermal fibroblasts or with mature collagen bundles. IGF-I localized strongly to epithelial cells of skin glands was weak to moderate in epidermis and blood vessels, and was absent in dermal cells. Weak focal staining for IGFBP-4 was found within uninjured epidermis. During wound healing, PAPP-A expression was induced in dermal granulation tissue within and adjacent to the injury. PAPP-A was present in dermis on d 2 and was increased in intensity and extent on d 8 and 14. PAPP-A expression also increased in the epidermis. PAPP-A expression in cells of granulation tissue colocalized with alpha-smooth actin staining of myofibroblasts and new blood vessels as well as with CD68 staining of macrophages and was associated with the compact, newly synthesized collagen of the healing wound. IGF-I staining was enhanced in the epidermis localized to the area of the incision and in granulation tissue associated with lymphoid cells. IGFBP-4 staining of the epidermis remained unchanged during wound healing, but was induced in the fibroblastic cells of granulation tissue over time. These data demonstrate localized and regulated expression of PAPP-A in human skin and suggest that PAPP-A may play an important role in an integrated IGF system in wound healing and tissue remodeling in vivo.

Forensic wound examination

Wound examination is of prime importance in forensic pathology, and it is desirable to establish a wound examination system in order to evaluate and record the nature of wound more accurately and objectively. Modern diagnostic techniques and devices as well as advanced cell-biological methods should be introduced as the means for this aim. For example, radiological, endoscopic or magnetic resonance imaging (MRI) examination have been used in addition to examination with the naked eye. In our department, a binocular surgical operating microscope is routinely employed at forensic autopsy, which is useful for elucidating the nature of wound in more detail. It is also necessary to determine whether a wound has vitality, and, if antemortem, how long before death the wound has been sustained. For the determination of wound age including vitality, various biological factors such as cytokines and extracellular matrix components involved in wound healing have been examined by histopathological methods. Our studies have shown that interleukin (IL)-1alpha, IL-1 b, IL-6, IL-10 and tumor necrosis factor-alpha are possibly useful markers for wound age determination as well as cell-biological indicators of vitality. Furthermore, molecular biological techniques have been intended to be applied to wound examination; our experimental study has shown that even mRNA of cytokines mentioned above can be histologically detected by reverse transcriptase-polymerase chain reaction or in situ hybridization. A trial of forensic wound examination from macroscopic to molecular level is discussed.

Advances in the diagnosis of wound vitality: a review

The diagnosis of the vital origin of wounds in many cases remains an unsolved problem for the forensic pathologist. Practical experience enables the expert to diagnose the vital or postmortem origin of wounds on the basis of macroscopic examination. In some cases, optic microscopy is used to confirm the diagnosis. In many other cases, additional more sensitive and specific markers of vitality are required. In the past 50 years, comprehensive research on this topic has resulted in a better understanding of the acute inflammatory reaction. The development and application of sensitive and specific markers through research in the areas of histochemistry, enzymology, and biochemistry has provided a partial solution to the problems involved in wound vitality diagnosis. A review of this challenging area of forensic pathology, including an explanation of these methods and markers, is presented in this paper.

Histological and enzyme histochemical parameters for the age estimation of human skin wounds

Routine histological staining techniques form the basis of a forensic age estimation of human skin wounds and the determination of vitality is aided by the detection of neutrophilic granulocytes which appear earliest about 20-30 min after wounding. A clear granulocyte infiltration and a significant increase in the number of macrophages indicates a post infliction interval of at least several hours. Macrophages containing incorporated particles such as lipophages, erythrophages or siderophages appear earliest at a wound age of 2-3 days similarly to extracellular deposits of hemosiderin, whereas the rarely detectable iron-free pigment hematoidin and spot-like lymphocytic infiltrates in the granulation tissue appear approximately one week or more after wounding. A complete reepithelialization of surgically treated and primarily healing human skin lesions can be expected earliest 5 days after wound infliction and the absence of a complete new epidermal layer indicates a survival time of less than 21 days. Enzyme histochemical methods allow a wound age differentiation especially in the range of a few hours. An increase in nonspecific esterases can be observed earliest approximately 1 hour after wounding followed by other enzymes such as acid phosphatase (approximately 2 h), ATPase (approximately 4 h), aminopeptidase (approximately 4 h) or alkaline phosphatase (approximately 4 h). Positive results, however, cannot be regularly found. Therefore, the detection of reactive changes is useful for a wound age estimation whereas negative findings, which in general must be interpreted with caution, can provide information only in a limited number of histological parameters.

The time-dependent localization of Ki67 antigen-positive cells in human skin wounds

A total of 77 human skin wounds with a post-infliction interval between 3 h and 7 months were investigated and the proliferation marker antigen Ki67 was visualized in paraffin sections using a specific monoclonal antibody (MIB). The re-built epidermal layer covering the former lesional area showed only a few basal cells positively staining for Ki67 antigen. No enhanced reactivity was found when compared to uninjured skin. In basal cells of the epidermis adjacent to the wound area, however, varying numbers of positive cells occurred, but no information useful for a reliable time estimation of skin wounds could be obtained due to the considerable variability in the number of Ki67 positive epidermal basal cells found in non-damaged skin. Fibroblastic cells in the wound area revealed an increased number of Ki67-positive sites which could first be detected in a 1.5-day-old skin lesion. Positive results could be obtained in every specimen investigated after a post-infliction interval of 6 days up to 1.5 months. Only the scar tissue of the oldest wound examined (wound age 7 months) revealed no increase in the number of positively staining fibroblasts. Therefore, positive results indicate a wound age of at least approximately 1.5 days and the lack of an increased number of positive fibroblastic cells in a sufficient number of specimens indicates at a wound age of less than 6 days, but cannot totally exclude longer post-infliction intervals.

Time-dependent pericellular expression of collagen type IV, laminin, and heparan sulfate proteoglycan in myofibroblasts

Human skin wounds (n = 62) with a wound age between 5 h and 6 weeks were investigated. The appearance of cell-associated pericellular basement membrane components collagen type IV, laminin and heparan sulfate proteoglycan (HSPG) in myofibroblasts was evaluated by immunohistochemistry. Laminin and HSPG were first detectable around myofibroblasts approximately 1.5 days after wounding. Collagen type IV did not appear before the 4th day after wound infliction. In wounds more than 7 days old, 94% of the cases showed fibroblastic cells positively staining for laminin, 70% of the wounds contained fibroblastic cells positive for HSPG and in 63% a positive reaction for collagen type IV was obtained around these cells. The numbers of the cases as well as of the cells positively stained for laminin exceeded the corresponding values for HSPG and especially for collagen type IV. The pericellular appearance of laminin or HSPG around myofibroblasts, therefore, indicates a wound age of at least approximately 1.5 days. The pericellular localization of collagen type IV indicates a survival time of approximately 4 days or more. Since these proteins are still detectable in the pericellular region of myofibroblasts in skin wounds with advanced wound age (6 weeks) further information for the time-estimation of older human skin lesions cannot be obtained. A semiquantitative analysis revealed no significant correlation between the number of positively stained cells and the wound age, rendering this parameter unsuitable for a practicable time-estimation of human wounds.