中性粒细胞胞外诱捕网在创面愈合过程中作用的研究进展

创面愈合与免疫及炎症反应密切相关。中性粒细胞作为炎症反应的主要效应细胞之一,已被证明在糖尿病足等创面愈合的病理生理过程中起着重要的作用。尤其是新近研究发现中性粒细胞在炎症、损伤等的刺激下,可以通过释放中性粒细胞胞外诱捕网(NET),抑制或阻碍创面的愈合,在创面愈合过程中起着重要的作用。然而,NET在不同类型的创面愈合中的作用还未完全阐明。本文将围绕免疫反应与炎症反应等在创面愈合中的最新研究进展,就NET在不同类型的创面愈合过程中的作用作一综述。     

Immuno-inflammatory cell dynamics during cutaneous wound healing

The process of wound healing begins with an inflammatory reaction that is principally dependent on cellular immune elements. Although the involvement in wound healing of leucocytes that mediate nonspecific immunity (e.g. neutrophils and macrophages) is well known, the participation of cells which prime the immune reaction, i.e. the lymphocytes, requires further investigation. This study was performed to examine the temporal sequence and kinetics of these cells during cutaneous wound repair. The model selected was a full-thickness skin excisional wound made on the flanks of female Wistar rats. At time points ranging from 3 h to 2 wk wound samples were processed for polyester wax-embedding. Target antigens were identified and monitored quantitatively in sections stained immunohistochemically. Monoclonal antibodies against neutrophils, macrophages, pan T cells and cytotoxic populations of lymphocytes were used. The results showed that these cells are involved in the process of wound healing in a distinctive dynamic pattern. The accumulation of CD3⁺ T lymphocytes in the wound bed was mainly associated with the phase of granulation tissue formation. Intraepithelial CD3⁺ T lymphocytes were detected in considerable numbers within the regenerating epidermis. The cytotoxic cell populations (OX8⁺) were classified morphologically into the cytotoxic/suppressor subset of T cells and NK cells. The OX8⁺ T cells were shown to have a kinetic pattern similar to CD3⁺ T lymphocytes but of a lower magnitude. The accumulation of OX8⁺ NK cells was confined to the early inflammatory phase of repair. It is concluded that CD3⁺ T lymphocytes as well as OX8⁺ cytotoxic populations of the immune system are involved in the process of cutaneous wound healing in temporal sequences which suggest that they may be involved in its modulation.     

Psychological factors and delayed healing in chronic wounds

OBJECTIVE: Studies have shown that stress can delay the healing of experimental punch biopsy wounds. This study examined the relationship between the healing of natural wounds and anxiety and depression. METHODS: Fifty-three subjects (31 women and 22 men) were studied. Wound healing was rated using a five-point Likert scale. Anxiety and depression were measured using the Hospital Anxiety and Depression Scale (HAD), a well-validated psychometric questionnaire. Psychological and clinical wound assessments were each conducted with raters and subjects blinded to the results of the other assessment. RESULTS: Delayed healing was associated with a higher mean HAD score (p = .0348). Higher HAD anxiety and depression scores (indicating "caseness") were also associated with delayed healing (p = .0476 and p = .0311, respectively). Patients scoring in the top 50% of total HAD scores were four times more likely to have delayed healing than those scoring in the bottom 50% (confidence interval = 1.06-15.08). CONCLUSIONS: The relationship between healing of chronic wounds and anxiety and depression as measured by the HAD was statistically significant. Further research in the form of a longitudinal study and/or an interventional study is proposed.     

The effect of PGG-beta-glucan on neutrophil chemotaxis in vivo

The beta-glucans are long-chain polymers of glucose in beta-(1,3)(1,6) linkages, which comprise the fungal cell wall and stimulate cells of the innate immune system. Previous in vitro studies have shown the ability of beta-glucan to increase the chemotactic capacity of human neutrophils. The current study examined an in vivo correlate of that observation by testing the hypothesis that systemic beta-glucan treatment would result in enhanced migration of neutrophils into a site of inflammation and improve antimicrobial function. A model of acute inflammation was used in which polyvinyl alcohol sponges were implanted subcutaneously into the dorsum of rats. Animals treated with beta-glucan showed a 66 +/- 6% and 186 +/- 42% increase in wound cell number recovered 6 and 18 h postwounding, respectively. Increased migration did not correlate with increased chemoattractant content of wound fluid, alterations in neutrophil-induced loss of endothelial barrier function, or changes in neutrophil adhesion to endothelial cells. Systemic administration of SB203580 abrogated the enhanced migration by beta-glucan without altering normal cellular entry into the wound. Studies also showed a priming effect for chemotaxis and respiratory burst in circulating neutrophils isolated from beta-glucan-treated animals. Heightened neutrophil function took place without cytokine elicitation. Furthermore, beta-glucan treatment resulted in a 169 +/- 28% increase in neutrophil number and a 60 +/- 9% decrease in bacterial load in the bronchoalveolar lavage fluid of Escherichia coli pneumonic animals. Taken together, these findings demonstrate that beta-glucan directly affects the chemotactic capacity of circulating neutrophils through a p38 mitogen-activated protein kinase-dependent mechanism and potentiates antimicrobial host defense.     

Photoperiod and stress affect wound healing in Siberian hamsters

Changes in day length alter several indices of immune function in Siberian hamsters. These experiments tested the hypothesis that photoperiodic changes in immune function are integrated at an organismal level as reflected by the ability to heal a cutaneous wound. Given the well-documented effects of psychological stressors on immune function, we also tested the hypothesis that photoperiod modulates the effects of acute stress on wound healing. Male hamsters were housed in long (16L:8D; LD) or short (8L:16D; SD) day lengths for 8+/-2 weeks. SD-treatment was sufficient to induce winter reproductive status. Hamsters then received a dermal punch wound. Hamsters were subjected to either 2 h of daily restraint stress or a control treatment for 3 days prior to and 5 days after wounding. Wounds were digitally photographed daily, and wound size was measured to quantify healing. Wounds of LD hamsters healed significantly faster than did those of SD hamsters. Restraint stress significantly accelerated healing in SD hamsters. The results suggest that the enhancing effects of short-term psychological stressors on immune function are apparent only when reproductive function is suppressed. In nature, enhanced wound healing coincident with the breeding season and territorial defense may be adaptive.     

The acceleration of wound healing in primates by the local administration of immunostimulatory CpG oligonucleotides

The process of wound healing involves complex interactions between circulating immune cells and local epithelial and endothelial cells. Studies in murine models indicate that cells of the innate immune system activated via their Toll-like receptors (TLR) can accelerate wound healing. This work examines whether immunostimulatory CpG oligodeoxynucleotides (ODN) designed to trigger human immune cells via TLR9 can promote the healing of excisional skin biopsies in rhesus macaques. Results indicate that 'K' type CpG ODN significantly accelerate wound closure in non-human primates (p < 0.05). Contributing to this outcome was a CpG-dependent increase in both the production of basic fibroblast growth factor and in keratinocyte migration. Of interest, IL-1α and TGFα normally present at sites of skin injury facilitated these effects. Current findings support the conclusion that the local administration of CpG ODN may provide an effective strategy for accelerating wound healing in humans.     

同种异体冷冻骨移植结合外固定架支撑修复大段骨缺损

背景：各种低温、细胞、免疫和灭菌去抗原技术的进步,使得大量的同种异体骨进入临床应用,给各类大段骨缺损的患者带来了希望。 目的：评价临床应用同种异体冷冻骨移植结合外固定架支撑治疗大段骨缺损的效果。 方法：利用同种异体冷冻骨移植治疗大段骨缺损36例,同时应用外固定架加压固定,提供力学支撑,在固定后定期回访。 结果与结论：随访1~24个月,失访1例,其余35例骨移植区骨质生长良好,9~20个月植骨骨化,无骨不连发生,各关节活动及肢体负重良好。部分患者肢体轻度肿胀,其中3例切口周围轻微红肿疼痛,4例患者伤口渗出较多,细菌培养阴性,涂片染色检查有浆细胞及淋巴细胞,中性粒细胞少,考虑为慢性免疫排斥反应所致,经过换药及应用泼尼松 3 d后分泌物减少,所有患者切口均一期愈合。结果可见同种异体冷冻骨移植结合外固定架加压固定是治疗大段骨缺损的有效治疗方法之一。     

Enhanced wound healing after emotional disclosure intervention

Objectives. Psychological stress is believed to impair wound healing via a down‐regulation of the immune system. Since previous research suggests that disclosure of tra‐umatic experiences can result in an up‐regulation of immune function, the present study aimed to investigate the impact of a disclosure intervention on the progress of wound healing. Design. The study used a prospective, longitudinal design with random assignment to the control (writing about time management) and experimental group (writing about a traumatic event). Methods. Participants (N = 36) completed questionnaires measuring perceived and emotional distress, loneliness, self‐esteem, social support, dispositional optimism, and health‐related behaviours. Accurate indication of the healing of a small punch biopsy wound was determined by using a high‐resolution ultrasound scanner. Results. Repeated measures ANOVA indicated that the disclosure intervention impacted wound healing. Participants who wrote about traumatic events had significantly smaller wounds 14 and 21 days after the biopsy compared with those who wrote about time management. Conclusions. It is concluded that a relatively brief and easy to administer intervention can have beneficial effects on wound healing. The potential for use in patient samples is indicated.     

Skin tissue engineering

The major applications of tissue-engineered skin substitutes are in promoting the healing of acute and chronic wounds. Several approaches have been taken by commercial companies to develop products to address these conditions. Skin substitutes include both acellular and cellular devices. While acellular skin substitutes act as a template for dermal formation, this discussion mainly covers cellular devices. In addressing therapeutic applications in tissue engineering generally, a valuable precursor is an understanding of the mechanism of the underlying pathology. While this is straightforward in many cases, it has not been available for wound healing. Investigation of the mode of action of the tissue-engineered skin substitutes has led to considerable insight into the mechanism of formation, maintenance and treatment of chronic wounds. Four aspects mediating healing are considered here for their mechanism of action: (i) colonization of the wound bed by live fibroblasts in the implant, (ii) the secretion of growth factors, (iii) provision of a suitable substrate for cell migration, particularly keratinocytes and immune cells, and (iv) modification of the immune system by secretion of neutrophil recruiting chemokines. An early event in acute wound healing is an influx of neutrophils that destroy planktonic bacteria. However, if the bacteria are able to form biofilm, they become resistant to neutrophil action and prevent reepithelialization. In this situation the wound becomes chronic. In chronic wounds, fibroblasts show a senescence-like phenotype with decreased secretion of neutrophil chemoattractants that make it more likely that biofilms become established. Treatment of the chronic wounds involves debridement to eliminate biofilm, and the use of antimicrobials. A role of skin substitutes is to provide non-senescent fibroblasts that attract and activate neutrophils to prevent biofilm re-establishment. The emphasis of the conclusion is the importance of preventing contaminating bacteria becoming established and forming biofilms.     

Delayed wound healing in the absence of intercellular adhesion molecule-1 or L-selectin expression

Inflammatory cells play a crucial role in wound healing, but the role of adhesion molecules including L-selectin and intercellular adhesion molecule-1 (ICAM-1) is not known in this process. We examined skin wound repair of excisional wounds in mice lacking L-selectin, ICAM-1, or both. The loss of ICAM-1 inhibited wound healing, keratinocyte migration from the edges of the wound toward the center, and granulation tissue formation. By contrast, L-selectin deficiency alone did not affect any of these parameters. However, the loss of both L-selectin and ICAM-1 resulted in inhibition of keratinocyte migration and granulation tissue formation beyond those caused by loss of ICAM-1 alone. Treatment of platelet-derived growth factor to the wounds normalized delayed wound healing in ICAM-1(-/-) mice, but not in L-selectin/ICAM-1(-/-) mice. Therefore, although ICAM-1 contributes to wound repair to a greater extent than L-selectin, a role for L-selectin was revealed in the absence of ICAM-1. The impaired wound repair was associated with reduced infiltration of neutrophils and macrophages in ICAM-1(-/-) and L-selectin/ICAM-1(-/-) mice. These results demonstrate a distinct role of ICAM-1 and L-selectin in wound healing and that the delayed wound healing in the absence of these molecules is likely because of decreased leukocyte accumulation into the wound site.     

Topical Estrogen Accelerates Cutaneous Wound Healing in Aged Humans Associated with an Altered Inflammatory Response

The effects of intrinsic aging on the cutaneous wound healing process are profound, and the resulting acute and chronic wound morbidity imposes a substantial burden on health services. We have investigated the effects of topical estrogen on cutaneous wound healing in healthy elderly men and women, and related these effects to the inflammatory response and local elastase levels, an enzyme known to be up-regulated in impaired wound healing states. Eighteen health status-defined females (mean age, 74.4 years) and eighteen males (mean age, 70.7 years) were randomized in a double-blind study to either active estrogen patch or identical placebo patch attached for 24 hours to the upper inner arm, through which two 4-mm punch biopsies were made. The wounds were excised at either day 7 or day 80 post-wounding. Compared to placebo, estrogen treatment increased the extent of wound healing in both males and females with a decrease in wound size at day 7, increased collagen levels at both days 7 and 80, and increased day 7 fibronectin levels. In addition, estrogen enhanced the strength of day 80 wounds. Estrogen treatment was associated with a decrease in wound elastase levels secondary to reduced neutrophil numbers, and decreased fibronectin degradation. In vitro studies using isolated human neutrophils indicate that one mechanism underlying the altered inflammatory response involves both a direct inhibition of neutrophil chemotaxis by estrogen and an altered expression of neutrophil adhesion molecules. These data demonstrate that delays in wound healing in the elderly can be significantly diminished by topical estrogen in both male and female subjects.     

Accelerated wound closure in neutrophil-depleted mice

The infiltration of neutrophils into injured tissue is known to protect wounds from invading pathogens. However, more recent studies suggest that neutrophils might inhibit the wound repair process. To investigate the role of neutrophils in wounds, mice were neutrophil-depleted by injection with rabbit anti-mouse neutrophil serum. Remarkably, epidermal healing, measured by wound closure, proceeded significantly faster in neutropenic than control mice (77.7+14.2% vs. 41.2+0.9%, P<0.02 at day 2). Dermal healing was not affected by neutrophil depletion, as neither collagen deposition nor wound-breaking strength was significantly different between neutropenic and control mice. As the delayed repair of diabetic individuals exhibits robust inflammation, the effect of neutrophil depletion on diabetic wound healing was investigated. Similar to the observations in wild-type mice, wound closure was accelerated by nearly 50% in neutropenic, diabetic mice. The results suggest that although neutrophils may provide protection against infection, they may retard wound closure.     

MRI tracking of transplanted iron‐labeled mesenchymal stromal cells in an immune‐compromised mouse model of critical limb ischemia

Peripheral arterial disease is a clinical problem in which mesenchymal stromal cell (MSC) transplantation may offer substantial benefit by promoting the generation of new blood vessels and improving limb ischemia and wound healing via their potent paracrine activities. MRI allows for the noninvasive tracking of cells over time using iron oxide contrast agents to label cells before they are injected or transplanted. However, a major limitation of the tracking of iron oxide‐labeled cells with MRI is the possibility that dead or dying cells will transfer the iron oxide label to local bystander macrophages, making it very difficult to distinguish between viable transplanted cells and endogenous macrophages in the images. In this study, a severely immune‐compromised mouse, with limited macrophage activity, was investigated to examine cell tracking in a system in which bystander cell uptake of dead, iron‐labeled cells or free iron particles was minimized. MRI was used to track the fate of MSCs over 21 days after their intramuscular transplantation in mice with a femoral artery ligation. In all mice, a region of signal loss was observed at the injection site and the volume of signal hypointensity diminished over time. Fluorescence and light microscopy showed that iron‐positive MSCs persisted at the transplant site and often appeared to be integrated in perivascular niches. This was compared with MSC transplantation in immune‐competent mice with femoral artery ligation. In these mice, the regions of signal loss caused by iron‐labeled MSC cleared more slowly, and histology revealed iron particles trapped at the site of cell transplantation and associated with areas of inflammation. Copyright © 2012 John Wiley & Sons, Ltd.     

体内移植羊膜对家兔肌腱损伤模型肌腱愈合的影响

研究的目的在于观察羊膜体内移植对肌腱损伤修复的影响。60 只跟腱损伤家兔动物模型采用同体对照动物实验方法,大体观察伤口愈合、肌腱粘连及肌腱肥大情况,并分别于术后第 2、4、6 周等3个时间点取跟腱,HE染色观察损伤区域炎细胞浸润和成纤维细胞数量,免疫组化染色观察胶原纤维排列塑形状况,拉伸试验测定肌腱弹性模量。另取 4 只家兔不做肌腱切断术作为正常对照,在第 0周 测定肌腱弹性模量。全部实验动物皮肤切口在术后 1 周 内基本愈合,未发生伤口感染情况。羊膜实验组跟腱粘连动物数量和肌腱断裂区域肥大程度低于阴性对照组(P<0.05)。术后第 2 周,两组动物炎症反应均达到最高值,但羊膜实验组炎细胞（包括中性粒细胞和单核细胞）浸润数量低于阴性对照组(P<0.05)。两组实验动物样本中成纤维细胞数量和胶原纤维积累数量无明显差异（P >0.05）,但羊膜实验组成纤维细胞和胶原纤维排列更具有序性,尤其是在术后第 6 周,明显好于阴性对照组。术后第 2 周和第4 周,羊膜实验组肌腱弹性模量均优于阴性对照组(P <0.05)。羊膜具有促进肌腱早期愈合和抗炎、抗粘连作用。     

The mevalonate pathway during acute tubular injury: selected determinants and consequences

Examination of thermally induced serosal lesions in mice displayed collections of inflammatory cells, predominantly macrophages, on and surrounding the wound within 48 hours of injury. Furthermore, by 2 days a large number of uninjured mesothelial cells adjacent to the wound were synthesizing DNA. From these findings, it was hypothesized that macrophages play a major role in serosal repair by stimulating mesothelial cell proliferation. Again, using a murine model of mesothelial regeneration, depletion of circulating monocytes significantly delayed serosal healing whereas addition of peritoneal exudate cells to the wound site 36 hours before injury increased the healing rate. In vivo assessment of mesothelial cell proliferation using tritiated thymidine incorporation and autoradiography demonstrated that peritoneal exudate cells stimulated mesothelial cell proliferation (12.44 +/- 1.63% labeling index, compared with controls in which medium only was used 4.48 +/- 0.71%). The mesothelial proliferation was predominantly because of macrophage-secreted products with molecular weights of 36 to 53 kd or 67 to 100 kd. These data support the hypothesis that macrophages play an important role in serosal healing by stimulating mesothelial cell proliferation.     

Inducible costimulator (ICOS) and ICOS ligand signaling has pivotal roles in skin wound healing via cytokine production

Skin wound healing is mediated by inflammatory cell infiltration of the wound site. Inducible costimulator (ICOS), expressed on activated T cells, and its ligand, ICOS ligand (ICOSL), expressed on antigen-presenting cells, have been considered a single receptor-ligand pair. Although the ICOS-ICOSL pathway participates in adaptive immunity, its roles in skin wound healing, which is mediated by innate immune responses, remain unknown. To clarify these roles, repair of excisional wounds was examined in ICOS(-/-) mice, ICOSL(-/-) mice, and ICOS(-/-)ICOSL(-/-) mice. Each mutant strain showed similar, dramatic delays in wound healing, especially at early times. Knockout mice showed suppressed keratinocyte migration, angiogenesis, and granulation tissue formation, and diminished T-cell, macrophage, and neutrophil infiltration. The loss of ICOS and/or ICOSL resulted in marked suppression of cytokine expression in wounds, especially the Th2 cytokines interleukin (IL)-4, IL-6, and IL-10. T-cell transfer experiments and T-cell depletion therapy further clarified the important roles of ICOS expressed on T cells and its interaction with ICOSL. Application of IL-6, but not IL-4, to the wounds significantly increased the onset of early wound healing in mutant mice. Thus, our results indicate that ICOS-ICOSL costimulatory signaling has critical roles during wound healing, most likely by inducing IL-6 production.     

Immune system-neuroendocrine dysregulation in spinal cord injury

Multiple communicative pathways among the nervous, endocrine and immune systems facilitate physiological immunoregulation. Spinal cord injury (SCI) patients have decreased natural (NK cell) and adaptive (T cell) immune function and reduced blood levels of cellular adhesion molecules (CAMs) that participate in immune function and wound healing. We found decreased LFA-1 and VLA-4 on peripheral blood leukocytes in SCI patients and lower levels of CAMs in SCT patients with pressure ulcers than in those without them. SCI might affect immune cells and immune responsiveness by: (1) disrupting the outflow of signals from the sympathetic nervous system to lymphoid tissues and their blood vessels as well as the returning afferent signals from these tissues to the brain; (2) immunosuppression caused by the stressors affecting SCI patients; (3) interrupting returning signals to the CNS from the periphery thereby reducing facilitation of immunoregulatory CNS neurons and decreasing their activity; or a combination of all three. SCI patients may develop dysregulation of the sympathetic nervous system that is intimately involved in immune function. Chronic stress mediates immunosuppression by corticosteroids, catecholamines, endorphins and met-enkephalin. The hypothalamus coordinates the response to stress through the release of soluble products from the sympathetic nervous system and hypothalamic-pituitary-adrenal axis. Whereas the nervous and endocrine systems are not concerned with immunological specificity, they do influence the intensity, kinetics and localization of immune responses. Products of an activated immune system may generate feedback circuits capable of inhibiting, enhancing or regulating neuronal input. Immune system cells can produce neurologically active peptides including ACTH, CRF, growth hormone, thyrotropin, prolactin, human chorionic gonadotropin, endorphin, enkephalins, substance P, somatostatin and VIP. Cytokines are likely important mediators of the HPA response to immune stimuli.     

Quantification of the wound healing using polarization-sensitive optical coherence tomography

We use polarization-sensitive optical coherence tomography (PS-OCT) to monitor the wound healing process in vitro and in vivo, which are affected by various drugs. Five rabbit subjects are used for in vitro studies and another five are used for in vivo studies. The in vitro studies are conducted to compare the PS-OCT images with histopathology. For each subject, three biopsy lesions are created on each ear: one site is not treated (control); the second site is treated with sphingosylphosphorylcholine, which is expected to promote healing; and the last is administered with tetraacetylphytosphingosine, which negatively affects the healing process. Each site is examined with a PS-OCT system at 1, 4, 7, 10, and 14- days after wound generation. The variations of phase retardation values caused by the collagen morphology changes on wound sites are quantified for all cases. Our results suggest that PS-OCT may be a useful tool for visualization of collagen fiber regeneration and for quantification of various drug effects during the wound healing process.     

Effect of fibrin sealant composition on human neutrophil chemotaxis

The use of fibrin sealants offers one of the most physiologically compatible approaches to preventing postoperative adhesions. Although a number of fibrin sealant formulations have been developed, little is known about how the various components of these preparations affect the wound-healing process. Because one of the key steps in wound healing is the migration of phagocytic leukocytes, such as neutrophils, into the site of injury, we performed studies to characterize systematically the effects of various fibrin sealant components on neutrophil chemotaxis. Using a transwell chemotaxis assay, we found that increasing fibrin concentration resulted in an inhibition of the ability of the cells to migrate through the clots in a dose-dependent manner, and at fibrin clot concentrations >2.0 mg/mL chemotaxis was completely blocked. Factor XIII crosslinking of the clots also had a significant impact on neutrophil chemotaxis, and sealant preparations deficient in Factor XIII allowed neutrophil migration at much higher fibrin concentrations. The presence of various other fibrin sealant components such as plasminogen and fibrinolysis inhibitors (aprotinin and tranexamic acid) did not have any significant effects on the ability of neutrophils to migrate through fibrin clots as compared to control clots without these components. Overall, these studies show that the composition of fibrin sealant preparations can significantly affect neutrophil migration into the site of injury, which could possibly influence the wound healing process.     

Growth arrest-specific 2 gene expression during patellar tendon healing

We examined the cellular and molecular processes involved in patellar tendon healing following induced injury. A wound was surgically created at the center of the patellar tendon of adult rats. The wound site was examined at selected time intervals by immunohistochemical and in situ hybridization techniques. It was found that, between the 2nd and 7th day postoperation, fibroblast-like cells invaded the wound site. DiI-labelling experiments suggested that the majority of cells that occupied the wound originated from the edges of the wound. Furthermore, immunohistochemical studies revealed that at the wound site a meshwork of fibronectin developed that can support the migration of the DiI-labelled cells. We also examined the spatial and temporal expression patterns of the growth arrest specific 2 (GAS2) gene during patellar tendon healing. GAS2 was found strongly expressed in the tenocytes of unoperated patellar tendons. The gene was also expressed in the intact regions of operated tendons but not in the fibroblast-like cells that occupied the wound site, when examined 2 days postoperation. In addition the strip of intact tendon directly opposite the wound site also did not express GAS2. Examination of the experimental tendon at the 3rd month, when cells had completely occupied the wound site, revealed that Gas2 was expressed by all cells found in the wound. Bromodeoxyuridine (BrdU) incorporation analysis revealed that the presence of Brdu-positive cells in the wound indirectly correlated with the absence of Gas2 expression. We speculate that the GAS2 gene might play a role in regulating tenocyte proliferation during tendon healing.