Apoptosis and p53 protein expression increase in the process of burn wound healing in guinea-pig skin

Highly Similar Tetramerization Domains from the p53 Protein of Different Mammalian Species Possess Varying Biophysical, Functional and Structural Properties

The p53 protein is a transcriptional regulatory factor and many of its functions require that it forms a tetrameric structure. Although the tetramerization domain of mammalian p53 proteins (p53TD) share significant sequence similarities, it was recently shown that the tree shrew p53TD is considerably more thermostable than the human p53TD. To determine whether other mammalian species display differences in this domain, we used biophysical, functional, and structural studies to compare the properties of the p53TDs from six mammalian model organisms (human, tree shrew, guinea pig, Chinese hamster, sheep, and opossum). The results indicate that the p53TD from the opossum and tree shrew are significantly more stable than the human p53TD, and there is a correlation between the thermostability of the p53TDs and their ability to activate transcription. Structural analysis of the tree shrew and opossum p53TDs indicated that amino acid substitutions within two distinct regions of their p53TDs can dramatically alter hydrophobic packing of the tetramer, and in particular substitutions at positions corresponding to F341 and Q354 of the human p53TD. Together, the results suggest that subtle changes in the sequence of the p53TD can dramatically alter the stability, and potentially lead to important changes in the functional activity, of the p53 protein.

Multifaceted roles of mitochondria in wound healing and chronic wound pathogenesis

Mitochondria are intracellular organelles that play a critical role in numerous cellular processes including the regulation of metabolism, cellular stress response, and cell fate. Mitochondria themselves are subject to well-orchestrated regulation in order to maintain organelle and cellular homeostasis. Wound healing is a multifactorial process that involves the stringent regulation of several cell types and cellular processes. In the event of dysregulated wound healing, hard-to-heal chronic wounds form and can place a significant burden on healthcare systems. Importantly, treatment options remain limited owing to the multifactorial nature of chronic wound pathogenesis. One area that has received more attention in recent years is the role of mitochondria in wound healing. With regards to this, current literature has demonstrated an important role for mitochondria in several areas of wound healing and chronic wound pathogenesis including metabolism, apoptosis, and redox signalling. Additionally, the influence of mitochondrial dynamics and mitophagy has also been investigated. However, few studies have utilised patient tissue when studying mitochondria in wound healing, instead using various animal models. In this review we dissect the current knowledge of the role of mitochondria in wound healing and discuss how future research can potentially aid in the progression of wound healing research.

Genome-wide DNA hypermethylation opposes healing in chronic wound patients by impairing epithelial-to-mesenchymal transition

An extreme chronic wound tissue microenvironment causes epigenetic gene silencing. An unbiased whole-genome methylome was studied in the wound-edge tissue of patients with chronic wounds. A total of 4,689 differentially methylated regions (DMRs) were identified in chronic wound-edge skin compared with unwounded human skin. Hypermethylation was more frequently observed (3,661 DMRs) in the chronic wound-edge tissue compared with hypomethylation (1,028 DMRs). Twenty-six hypermethylated DMRs were involved in epithelial-mesenchymal transition (EMT). Bisulfite sequencing validated hypermethylation of a predicted specific upstream regulator TP53. RNA-Seq analysis was performed to qualify findings from methylome analysis. Analysis of the downregulated genes identified the TP53 signaling pathway as being significantly silenced. Direct comparison of hypermethylation and downregulated genes identified 4 genes, ADAM17, NOTCH, TWIST1, and SMURF1, that functionally represent the EMT pathway. Single-cell RNA-Seq studies revealed that these effects on gene expression were limited to the keratinocyte cell compartment. Experimental murine studies established that tissue ischemia potently induces wound-edge gene methylation and that 5′-azacytidine, inhibitor of methylation, improved wound closure. To specifically address the significance of TP53 methylation, keratinocyte-specific editing of TP53 methylation at the wound edge was achieved by a tissue nanotransfection-based CRISPR/dCas9 approach. This work identified that reversal of methylation-dependent keratinocyte gene silencing represents a productive therapeutic strategy to improve wound closure.

Effects of Pulsed 810 nm Al-Ga-As Diode Laser on Wound Healing Under Immunosuppression: A Molecular Insight

BACKGROUND AND OBJECTIVES

Dysregulated inflammation is one of the major contributing factors for the prevalence of non-healing chronic wound in immunosuppressed subjects. Photobiomodulation (PBM) has emerged as a potential non-thermal, light-based therapeutic healing intervention for the treatment of impaired wounds.

STUDY DESIGN/MATERIALS AND METHODS

The present study delineates the underlying molecular mechanisms of PBM 810 nm laser-induced full-thickness cutaneous wound repair in immunosuppressed rats at continuous and pulsed wave-mode with power-density of 40 mW/cm ² , fluence 22.6 J/cm ² for 10 minutes daily for 7 post-wounding days. Molecular markers were assessed using biochemical, enzyme-linked immunosorbent assay quantification, enzyme kinetics and immunoblots analyses pertaining to inflammation, oxidative stress, cell survival, calcium signaling, and proliferation cascades.

RESULTS

Results distinctly revealed that pulsed 810 nm (10 Hz) PBM potentially influenced the cell survival and proliferation signaling pathway by significantly upregulated phospho-protein kinase B(phospho-Akt), phospho-extracellular-signal-regulated kinase 1 (ERK1), transient receptor potential vanilloid-3 (TRPV3), Ca²⁺ , calmodulin, transforming growth factor-β1 (TGF-β1), TGF-βR3, and Na ⁺ /K ⁺ -ATPase pump levels. PBM treatment resulted in reduction of exaggerated inflammatory responses evident by significantly repressed levels of interleukin-1β (IL-1β), IL-6, cyclooxygenase 2 (COX-2), and substance-P receptor (SPR), as well as inhibited apoptotic cell death by decreasing p53, cytochrome C, and caspase 3 levels (P < 0.05), which, in turn, effectively augment the wound repair in immunosuppressed rats. PBM treatment also lowered 4-hydroxynoneal (HNE) adduct level and NADP/NADPH ratio and upregulated the GRP78 expression, which might culminate into reduced oxidative stress and maintained the redox homeostasis.

CONCLUSIONS

Taken together, these findings would be helpful in better understanding of the molecular aspects involved in pulsed 810 nm laser-mediated dermal wound healing in immunosuppressed rats through regulation of cell survival and proliferation via Ca²⁺ -calmodulin, Akt, ERK, and redox signaling. Lasers Surg. Med. © 2019 Wiley Periodicals, Inc.

Role of inducible nitric oxide synthase and interleukin-6 expression in estimation of skin burn age and vitality

Estimation of age and vitality of burn injury both in the living and dead is essential in forensic practice. Nitric oxide and interleukin-6 (IL-6) play an important role in skin burn healing. In this study, the expression of inducible nitric oxide synthase (iNOS) and IL-6 proteins during skin burn healing in rats was studied for purposes of burn dating and to differentiate between ante-mortem and post-mortem burn. Ante-mortem skin burns were created on forty five rats. Normal and burnt skin samples were taken at 1, 3, 5, 7, 9, 11, 13, 15 and 21 days following burn induction (5 rats for each stage). Post-mortem burn was inflicted 6 h after scarification in another five rats. There was a statistically significant difference in both iNOS and IL-6 expression between the different time intervals of the ante-mortem burn. Expression of both iNOS and IL-6 decreased remarkably in the post-mortem burn with a statistically significant difference from ante-mortem intervals. A statistically significant positive association between the two markers was found. These results indicate that both iNOS and IL-6 expression in ante-mortem burnt skin was time dependent and significantly differed from post-mortem burn. Further research on humans is recommended.

Effect of combined radiation injury on cell death and inflammation in skin

In the event of a nuclear disaster, the individuals proximal to the source of radiation will be exposed to combined radiation injury. As irradiation delays cutaneous repair, the purpose of this study was to elucidate the effect of combined radiation and burn injury (CRBI) on apoptosis and inflammation at the site of skin injury. Male C57Bl/6 mice were exposed to no injury, thermal injury only, radiation only (1 and 6 Gy) and CRBI (1 and 6 Gy) and euthanized at various times after for skin collection. TUNEL staining revealed that the CRBI 6 Gy group had a delayed and increased apoptotic response. This correlated with decreased recovery of live cells as compared to the other injuries. Similar response was observed when cleaved-caspase-3 immunohistochemical staining was compared between CRBI 6 Gy and thermal injury. TNFR1, caspase 8, Bax and IL-6 mRNA expression revealed that the higher CRBI group had delayed increase in mRNA expression as compared to thermal injury alone. RIPK1 mRNA expression and necrotic cell counts were delayed in the CRBI 6 Gy group to day 5. TNF-α and NFκB expression peaked in the CRBI 6 Gy group at day 1 and was much higher than the other injuries. Also, inflammatory cell counts in the CRBI 6 Gy group were lower at early time points as compared to thermal injury by itself. These data suggest that CRBI delays and exacerbates apoptosis and inflammation in skin as well as increases necrosis thus resulting in delayed wound healing.

Transforming growth factor-beta1-antisense modulates the expression of hepatocyte growth factor/scatter factor in keloid fibroblast cell culture

Abnormal wound healing processes can result in hypertrophic scars and keloids. Transforming growth factor-beta1 (TGF-beta1) and hepatocyte growth factor/scatter factor (HGF/SF) are biphasic growth factor cytokines in physiologic and pathophysiologic conditions. Findings have shown TGF-beta1 to be pivotal in the formation of keloid tissue. Therefore, neutralizing antibodies may allow wound healing without keloid formation. As reported, TGF-beta1 is antagonized by HGF/SF. Some authors have reported that exogenous administration of HGF/SF prevented scar formation. Hence, this study targeted TGF-beta1 and determined the levels of HGF/SF in fibroblast cell culture. Keloid tissue was taken from seven patients. Another seven patients with mature nonhypertrophic scar served as controls. All tissues were cultured, and fibroblast cultures were used for further experiments. The TGF-beta1 antisense was administered at 3 and 6 micromol/ml, and HGF/SF levels were determined after 16, 24, and 48 h of incubation. The levels of HGF/SF showed significant differences after incubation with antisense oligonucleotides. The increasing antisense levels resulted in increased HGF/SF levels (up to 87.66 pg/ml after 48 h of incubation). In conclusion, targeting TGF-beta1 resulted in significantly increased levels of HGF/SF. The clinical relevance could include the use of locally administered HGF/SF in protein or gene form to minimize formation of keloids. Nevertheless, wound healing is the result of many interacting cytokines, so neutralizing or targeting one protein could result in no significant effect.

Pifithrin-alpha, an inhibitor of p53 transactivation, alters the inflammatory process and delays tendon healing following acute injury

Transcription factor p53, which was initially associated with cancer, has now emerged as an important regulator of inflammation and extracellular matrix homeostasis, two processes highly relevant to tendon repair. The goal of this study was to evaluate the effect of a p53 transactivation inhibitor, namely, pifithrin-alpha, on the pathophysiological sequence following collagenase-induced tendon injury. Administration of pifithrin-alpha during the inflammatory phase reduced the accumulation of neutrophils and macrophages by 30 and 40%, respectively, on day 3 postinjury. Pifithrin-alpha failed to reduce the percentage of apoptotic cells following collagenase injection but delayed functional recovery. In uninjured Achilles tendons, pifithrin-alpha increased metalloprotease activity 2.4-fold. Accordingly, pifithrin-alpha reduced the collagen content in intact tendons as well as in injured tendons 7 days posttrauma compared with placebo. The effect of pifithrin-alpha on load to failure and stiffness was also evaluated. The administration of pifithrin-alpha during the inflammatory phase did not significantly decrease the functional deficit 3 days posttrauma. More importantly, load to failure and stiffness were significantly decreased in the pifithrin-alpha group from day 7 to day 28 compared with placebo. Overall, our results suggest that administration of pifithrin-alpha alters the inflammatory process and delays tendon healing. The present findings also support the concept that p53 can regulate extracellular matrix homeostasis in vivo.

Activating transcription factor 3, a stress sensor, activates p53 by blocking its ubiquitination

Activating transcription factor 3 (ATF3) is rapidly induced by diverse environmental insults including genotoxic stress. We report herein that its interaction with p53, enhanced by genotoxic stress, stabilizes the tumor suppressor thereby augmenting functions of the latter. Overexpression of ATF3 (but not a mutated ATF3 protein (Delta102-139) devoid of its p53-binding region) prevents p53 from MDM2-mediated degradation and leads to increased transcription from p53-regulated promoters. ATF3, but not the Delta102-139 protein, binds the p53 carboxy-terminus and diminishes its ubiquitination and nuclear export. Genotoxic-stressed ATF3-null mouse embryonic fibroblasts, or cells in which ATF3 was reduced by small interference RNA, show inefficient p53 induction and impaired apoptosis compared with wild-type cells. ATF3-null cells (but not wild-type cells), which poorly accumulate p53, are transformed by oncogenic Ras. Thus, ATF3 is a novel stress-activated regulator of p53 protein stability/function providing the cell with a means of responding to a wide range of environmental insult, thus maintaining DNA integrity and protecting against cell transformation.

Local administration of hepatocyte growth factor gene enhances the regeneration of dermis in acute incisional wounds

Hepatocyte growth factor (HGF) has a number of biological activities, e.g., mitogenic, motogenic, antiapoptotic, antifibrous, and morphogenic. It also has angiogenic and angioprotective activities for endothelial cells. The aim of this study was to characterize the role of HGF in wound healing by administering the HGF gene locally to acute incisional skin wounds created on the backs of rats. To create wounds, the backs of Wistar rats were clipped and three 2-cm-long incisional wounds were made deep to the fascia. The wounds contained pannicrus carnosum and were created at intervals of 2 cm. After suturing, the HGF gene was then administered intradermally. Apoptotic cells in wound lesions were identified by TUNEL method as well as by immunological detection of active caspase-3. In the HGF-treated animals, we found almost complete suppression of apoptosis and well-organized wound healing. Histopathological examination revealed that the proliferation of fibroblasts was suppressed and that scar formation was less apparent in the HGF-treated animals compared to the controls. It is thought that administration of the HGF gene immediately after surgery may enhance the healing process through suppressing apoptosis, which occurred in the controls 1 week after suturing the incisional wound. In addition, locally increased HGF expression due to the introduction of the HGF gene to cells around wounds enhances dermal regeneration, possibly by promoting regeneration of dermal tissue, which results in less scarring due to its antifibrotic effect. Thus, HGF supplementation through gene therapy may be an effective strategy for treating wounds, as it increases the regeneration of the dermis to allow for "scarless wound healing."

Purinergic receptor expression in the regenerating epidermis in a rat model of normal and delayed wound healing

This study investigated changes in the protein expression of purinergic receptors in the regenerating rat epidermis during normal wound healing, in denervated wounds, and in denervated wounds treated with nerve growth factor (NGF), where wound healing rates are normalized. Excisional wounds were placed within denervated, pedicled, oblique, groin skin flaps, and in the contralateral abdomen to act as a control site. Six rats had NGF-treated wounds and six had untreated wounds. Tissue was harvested at day four after wounding. The re-epithelializing wound edges were analyzed immunohistochemically for P2X(5), P2X(7), P2Y(1) and P2Y(2) receptors, and immunostaining of keratinocytes was quantified using optical densitometry. In normal rat epidermis, P2Y(1) and P2Y(2) receptors were found in the basal layer where keratinocytes proliferate; P2X(5) receptors were associated with proliferating and differentiating epidermal keratinocytes in basal and suprabasal layers; P2X(7) receptors were associated with terminally differentiated keratinocytes in the stratum corneum. In the regenerating epidermis of denervated wounds, P2Y(1) receptor protein expression was significantly increased in keratinocytes (P<0.001) but P2Y(1) receptors (P<0.001) compared with untreated denervated wounds. In innervated wounds, NGF treatment enhanced expression in keratinocytes. P2X(5) (P>0.001) and P2Y(1) receptor protein (P<0.001) expression in keratinocytes. P2X(7) receptors were absent in all experimental wound healing preparations. P2X(5), P2X(7), P2Y(1) and P2Y(2) receptor protein expression in the regenerating epidermis was altered both during wound healing and also by NGF treatment. Possible roles for purinergic signalling and its relation to NGF in wound healing are discussed.

Functional and morphologic properties of a modified mesh for inguinal hernia repair

Inguinal hernia repair is one of the most frequently performed operations. Next to conventional techniques, open and laparoscopic tension-free methods using mesh implants to reinforce the abdominal wall are increasingly carried out, even becoming the standard procedure in many countries. Because of the benefits of material-reduced meshes for incisional hernia repair, a new mesh modification for tension-free inguinal hernia repair has been developed. In the present study this new low-weight mesh (Vypro II) made of polypropylene and polyglactin multifilaments was compared to a common heavy-weight polypropylene mesh (Prolene) regarding their functional consequences and the morphologic tissue response. After implantation in rats as an inlay, abdominal wall mobility was recorded by three-dimensional photogrammetry and the tensile strength of the suture zone and the mesh itself was measured at 3, 21, and 90 days. Explanted tissue samples have been investigated for their histologic reaction in regard to the inflammatory infiltrate, vascularization, and connective and fat tissue ingrowth. Numbers of granulocytes, macrophages, fibroblasts, lymphocytes, and foreign giant body cells have been evaluated to reflect the quality of the tissue response. The cellular response was assessed by measuring DNA strand breaks and apoptosis (TUNEL), proliferation (Ki67), and cell stress (HSP70). The results indicated that restriction of abdominal wall mobility was significantly reduced with Vypro II compared to that seen with heavy-weight mesh modification, and the inflammatory reaction and connective tissue formation were markedly diminished. Apoptosis and cell proliferation showed considerably lowered levels, and expression of cytoprotective HSP70 was significantly increased. The present study thus confirms the benefits of material-reduced mesh modifications. The new low-weight mesh (Vypro II) could be advantageous in inguinal hernia repair.

Protective effect of topical iodine preparations upon heat-induced and hydrofluoric acid-induced skin lesions

In this study, the protective prophylactic and post-exposure effects of novel topical iodine preparations were demonstrated upon heat- and hydrofluoric acid-induced skin lesions in the haired guinea pig. Prophylactic treatment of thermal bums with a liquid iodine preparation resulted in statistically significant reductions of 39% and 30%, respectively, in acute inflammation and hemorrhage-microscopic dermal parameters indicative of acute tissue damage. A clear trend of iodine-induced reduction in dermal necrosis occurred, and the epidermal healing markers, acanthosis and hyperkeratosis, were increased. Postexposure treatment of thermal burns with an iodine ointment preparation immediately after occurrence also conferred significant therapeutic reduction in parameters of tissue damage such as epidermal ulceration (87%), acute inflammation (58%), and hemorrhage (30%). Gross pathological evaluation showed that prophylactic and postexposure treatments with the liquid iodine preparation significantly reduced the heat-induced ulceration area by 97% and 65%, respectively. In addition, immediate treatment with an ointment iodine formulation significantly decreased the ulceration area by 98%; its tetraglycol vehicle also had a beneficial effect. Postexposure treatment with the iodine ointment proved efficacious upon hydrofluoric acid-induced skin burns. We observed statistically significant reductions of 76% and 68% in ulceration areas at intervals of 5 and 10 minutes between exposure and treatment, whereas a weaker effect was observed at a longer time interval of 15 minutes. Our findings suggest the therapeutic usage of these newly developed iodine preparations for thermally induced and hydrofluoric acid-induced skin burns.

Impact of polymer pore size on the interface scar formation in a rat model

BACKGROUND

The surgical therapy of hernias is increasingly based on reinforcement with alloplastic material, in particular surgical meshes. The biological response to these foreign bodies largely depends on the selected material and its structure. In comparison to the physiological scar process following a simple abdominal wall incision, the chronic inflammation at the interface to the polymers lead to specific morphological alterations.

MATERIALS AND METHODS

In the present study two meshes with different pore sizes were implanted into rats: a heavy-weight and small-pore-sized mesh (hw-mesh) made of nonabsorbable polypropylene monofilaments and a low-weight large-pore-sized mesh consisting of polypropylene and of absorbable polyglactin multifilaments (lw-mesh). A suture repair of a laparotomy served as control. After 7, 14, 21, and 90 days the mesh area was analyzed with regard to tissue and cellular response.

RESULTS

Over the whole observation period morphometric analysis indicated an improved integration of the lw-mesh with reduction of both inflammation and fibrosis, whereas the hw-mesh induced an intense chronic inflammation concomitant with an intensified bridging scar reaction. On the cellular level these findings correspond to an elevated cell turnover, characterized by increased rates of apoptotic and proliferating cells. In contrast, the tissue reaction to the lw-mesh achieved levels almost similar to those of the physiological scaring process in the control group.

CONCLUSION

In conclusion, the present data confirm the development of a chronic inflammatory foreign body reaction at the interface to both hw-meshes and lw-meshes; however, the use of lw-meshes showed superior tissue integration. With regard to the quite similar polymer surface the pore size appears to be of major importance in tissue reaction and for the biocompatibility of mesh structures.

Demonstration of apoptosis in human skin injuries as an indicator of vital reaction

Demonstrating the vital character of an injury and estimation of the age are routine tasks in forensic pathology and although many different techniques have been applied to this problem none have been found to be completely satisfactory. Apoptosis, an active genetically controlled process, is the major mechanism by which homeostasis of a number of physiological systems in the body is regulated and changes in the rate following different kinds of stimuli have prompted us to test it as an indicator of vitality. We used an in situ end-labelling technique (Apop-Tag) in 30 human surgical skin injuries with age since injury ranging from 3 min to 8 h and found that apoptotic keratinocytes are found in over 50% of the cases with a post-infliction interval of at least 120 min. Apoptosis was not seen in injuries less than 120 min old or in normal skin, which was used as an external control. These results suggest that apoptosis could be a useful indicator for the intravital occurrence of injuries and could help to estimate the date of the skin injuries in some cases. The importance of strict technical control is stressed and the necessity of a complementary technique to confirm apoptosis is discussed.

Chemoprotection from p53-dependent apoptosis: potential clinical applications of the p53 inhibitors

The p53 tumor suppressor pathway is a key mediator of stress response that protects the organism from accumulating genetically altered and potentially cancerous cells by inducing growth arrest or apoptosis in damaged cells. However, under certain stressful conditions, p53 activity can result in massive apoptosis in sensitive tissues, leading to severe pathological consequences for the organism. One such situation is anticancer therapy that is often associated with general genotoxic stress, leading to p53-dependent apoptosis in the epithelia of the digestive tract and in the hematopoietic system. A chemical inhibitor of p53, capable of suppressing p53-mediated apoptosis, was shown to protect mice from lethal doses of gamma-radiation, making pharmacological suppression of p53 a perspective therapeutic approach to reduce the side-effects of cancer treatment. There are other situations, besides anti-cancer therapy, when humans are exposed to stressful conditions known to involve p53 activation, which, in extreme cases, could result in the development of life-threatening diseases. Here we review the experimental evidence on the role of p53 in tissue injuries associated with hypoxia (heart and brain ischemias) and hyperthermia (fever and burns), comparing these pathologies with the consequences of genotoxic stress of cancer treatment. The accumulated information points to the involvement of p53 in the generation of the pathological outcome of the above stresses, making them potential targets for the therapeutic application of p53 inhibitors.

Spatial and temporal expression of basic fibroblast growth factor protein during wound healing of rat skin

BACKGROUND

Basic fibroblast growth factor (bFGF) stimulates the mitogenesis of various cells and plays a key part in wound healing.

OBJECTIVES

To determine the spatial and temporal expression of bFGF protein during wound healing after burning of rat skin.

METHODS

Immunohistochemical methods were used.

RESULTS

The immunostaining for bFGF in the normal epidermis was faint and sporadic in the basal cell layer. However, significant staining for bFGF was found in four locations: regenerated epidermis, a band-like zone near the regenerated epidermis, renewed capillaries, and cells infiltrating into the granulation tissue at the inflammatory to proliferative stages after the burn. The intensity of immunostaining of regenerated epidermis, the band-like zone and renewed capillaries was maximal during the proliferative stage and decreased to normal levels or disappeared simultaneously with wound closure. Immunopositive macrophage-like cell numbers in the granulation tissue increased during the proliferative stage and promptly decreased after wound closure, but such cells were only poorly visible in the scar tissue until 42 days postburn.

CONCLUSIONS

bFGF may affect the proliferation, differentiation and migration of regenerated keratinocytes and the recruitment of inflammatory cells, as well as neovascularization in granulation tissue during wound healing. Macrophages may play a pivotal role in cutaneous wound repair by producing bFGF not only during the inflammatory or proliferative stages but also during the remodelling stage.

Enhanced expression of caspase-3 in hypertrophic scars and keloid: induction of caspase-3 and apoptosis in keloid fibroblasts in vitro

Recent studies have suggested that the regulation of apoptosis during wound healing is important in scar establishment and development of pathological scarring. To examine the phenomenon of apoptosis and its involvement in the process of pathological scarring, we immunohistochemically quantified differential levels of expression of caspase-3 and -2, which are activated during apoptosis in vitro, in surgical resected scar tissues. We divided 33 cases of normally healed flat scars and 18 cases of pathological scars (15 cases of hypertrophic scars and 3 cases of keloid) into three groups (S1 = <10 months' duration; S2 = 10 to 40 months' duration; and S3 = >40 months' duration) according to the duration of scar. In all three groups examined, the semiquantitative scores for caspase-3 staining were significantly higher for the combination of hypertrophic scars and keloid as a group compared with normally healed flat scars, suggesting reduced cell survival and increased apoptotic cell death in hypertrophic scars and keloid. Apoptosis and caspase proteolytic activities were examined in vitro using two flat scar-derived fibroblast lines (FSFB-1 and -2) and two keloid-derived fibroblast lines (KFB-1 and -2). After 24 hours of serum deprivation, apoptotic cells were significantly increased in both KFB lines, whereas serum deprivation of FSFB-1 cells did not result in a significant increase in apoptotic cell number. After serum deprivation, significant increases in caspase-3 proteolytic activities were detected in both KFB lines compared with both FSFB lines. In contrast, no significant differences with caspase-8 activity were observed between similarly treated KFB and FSFB lines. Furthermore, serum deprivation-induced apoptosis of KFB-2 cells was significantly inhibited by the caspase-3 inhibitor Ac-Asp-Glu-Val-Asp-fluoromethyl ketone (DEVD-FMK), indicating that caspase-3 is important for serum deprivation-induced apoptosis in KFB-2 cells. Considering the role of caspase-3 as a key effector molecule in the execution of apoptotic stimuli, our results suggested that enhanced expression of caspase-3 in hypertrophic scars and keloid induces apoptosis of fibroblasts, which may play a role in the process of pathological scarring.