LETTERS TO THE EDITOR
Angiogenin, an angiogenic factor with potential for tissue engineering applications
To the Editor: We read, with great interest, the serial articles published by Pan and colleagues.1,2 The authors describe that burn blister fluid contains large amounts of bioactive factors, and angiogenin (Ang) has been identified as the main component involved in the induction of early-stage neovascularization.1 The expression level of Ang in deep partial thickness burns is higher than that in superficial partial thickness burns. Ang alone was shown to be sufficient to induce endothelial differentiation of circulating angiogenic cells without the involvement of vascular endothelial growth factor A (VEGF-A).2 Such studies are encouraging and of major interest. Since our research team has been focusing on the applications of Ang in tissue engineering, we would like to introduce our understanding to Ang and angiogenesis. Angiogenesis represents a critical problem in tissue engineering that must be solved.3 Cytokines and growth factors, with the potential for angiogenic stimulation, play important roles in regulating the process of angiogenesis. To date, numerous angiogenic factors, e.g., VEGF, acidic and basic fibroblast growth factors (aFGF and bFGF, respectively), and epidermal growth factor (EGF), have been used to promote angiogenesis in conjunction with various delivery systems. Ang, first isolated from the serum-free supernatant of an established human adenocarcinoma cell line (HT-29),4 has been shown to play roles in tumorigenesis and angiogenesis.5 However, Ang is not a tumor-specific product; it is also expressed in normal cells and plasma.6,7 Ang is a normal constituent of the circulation and is present in the vasculature that rarely undergoes proliferation.8 Some groups suggested that Ang is a general requirement for cell proliferation and angiogenesis induced by various other angiogenic proteins, including VEGF, FGF, and EGF; inhibitors of the nuclear translocation of Ang were shown to abolish the angiogenic activities of these factors.9 Ang is the only member of the ribonuclease (RNase) superfamily with angiogenic activity and is also unique as the only angiogenic factor with RNase activity.4 Ang acts selectively on vascular endothelial cells (ECs) and smooth muscle cells (SMCs) to promote their proliferation, migration, and adhesion, inhibiting apoptosis, and to stimulate the ECs to form new vessels.10,11 Ang can also translocate into the nucleus where it acts as an RNase.12 Although the RNase activity of Ang is rather weak, it is critical due to its angiogenic properties. Ang is an important angiogenic factor in many physiological and pathological conditions. For example, the expression levels of Ang increase from 150 to 250 ng/mL between weeks 10 and 40 in the pregnancies.13 Pan et al. found the higher expression of Ang in the deep partial partial thickness burns.1 The angiogenic activity of Ang depends on its interaction with ECs and SMCs, as well as on its RNase activity, matrix 288
degradation, and participation in several signal transduction pathways.10 Although the angiogenic function of Ang has been confirmed,5 its potential applications in tissue engineering have seldom been discussed. Our research group began focusing on the role of Ang in early-stage angiogenesis. In previous work, a controlled Ang delivery system was established by heparinizing Ang into porous collagen-chitosan scaffolds; the results indicated that Ang was released from the heparinized scaffolds in a controlled manner, and the presence of Ang enhanced angiogenesis of the heparinized scaffold after subcutaneous implantation into rabbits.14 However, this type of protein delivery system may not be ideal because Ang proteins with very short half-lives in vivo may be denatured by the loading processes used to protect them from degradation and allow for prolonged release. Hence, further studies may employ gene-activated scaffolds to realize sustained delivery of Ang, thus promoting angiogenesis.15 To date, both Ang gene and protein, e.g., Ang plasmid DNA and recombinant human Ang protein, can be obtained easily. Various delivery systems have been constructed using physical or chemical methods. Of course, some other applications of Ang can also be developed. To sum up, this angiogenic factor has great potential to solve the angiogenesis insufficiency of tissueengineered constructs in the early stages.
ACKNOWLEDGMENTS This work was financially supported by the Natural Science Foundation of Zhejiang (LQ12H15001) and the Grand Science and Technology Special program of Zhejiang (2007C13040). Xingang Wang, PhD1; Yuanhai Zhang, BS2; Chunmao Han, PhD, MD1 1. Department of Burns & Wound Care Centre, Second Affiliated Hospital of Zhejiang University, Hangzhou and 2. Department of Burn and Plastic Surgery, Quhua Hospital, Quzhou, China
REFERENCES 1. Pan SC, Wu LW, Chen CL, Shieh SJ, Chiu HY. Deep partial thickness burn blister fluid promotes neovascularization in the early stage of burn wound healing. Wound Repair Regen 2010; 18: 311–18. 2. Pan SC, Wu LW, Chen CL, Shieh SJ, Chiu HY. Angiogenin expression in burn blister fluid: implications for its role in burn wound neovascularization. Wound Repair Regen 2012; 20: 731–9. Wound Rep Reg (2014) 22 288–289 © 2014 by the Wound Healing Society
Letters to the Editor
3. Novosel EC, Kleinhans C, Kluger PJ. Vascularization is the key challenge in tissue engineering. Adv Drug Deliv Rev 2011; 63: 300–11. 4. Fett JW, Strydom DJ, Lobb RR, Alderman EM, Bethune JL, Riordan JF, et al. Isolation and characterization of angiogenin, an angiogenic protein from human carcinoma cells. Biochemistry 1985; 24: 5480–6. 5. Xia WR, Fu WL, Cai L, Cai X, Wang YY, Zou MJ, et al. Expression, purification and characterization of recombinant human angiogenin in Pichia pastoris. Biosci Biotechnol Biochem 2012; 76: 1384–8. 6. Rybak SM, Fett JW, Yao QZ, Vallee BL. Angiogenin mRNA in human tumor and normal cells. Biochem Biophys Res Commun 1987; 146: 1240–8. 7. Shapiro R, Strydom DJ, Olson KA, Vallee BL. Isolation of angiogenin from normal human plasma. Biochemistry 1987; 26: 5141–6. 8. Tello-Montoliu A, Patel JV, Lip GY. Angiogenin: a review of the pathophysiology and potential clinical applications. J Thromb Haemost 2006; 4: 1864–74. 9. Kishimoto K, Liu S, Tsuji T, Olson KA, Hu GF. Endogenous angiogenin in endothelial cells is a general requirement for
10. 11.
12.
13.
14.
15.
cell proliferation and angiogenesis. Oncogene 2005; 24: 445– 56. Gao X, Xu Z. Mechanisms of action of angiogenin. Acta Biochim Biophys Sin (Shanghai) 2008; 40: 619–24. Bond MD, Vallee BL. Isolation and sequencing of mouse angiogenin DNA. Biochem Biophys Res Commun 1990; 171: 988–95. Shapiro R, Vallee BL. Human placental ribonuclease inhibitor abolishes both angiogenic and ribonucleolytic activities of angiogenin. Proc Natl Acad Sci U S A 1987; 84: 2238– 41. Eleftheriadis T, Kartsios C, Pissas G, Liakopoulos V, Antoniadi G, Galaktidou G, et al. Increased plasma angiogenin level is associated and may contribute to decreased T-cell zeta-chain expression in hemodialysis patients. Ther Apher Dial 2013; 17: 48–54. Shi H, Han C, Mao Z, Ma L, Gao C. Enhanced angiogenesis in porous collagen-chitosan scaffolds loaded with angiogenin. Tissue Eng Part A 2008; 14: 1775–85. Storrie H, Mooney DJ. Sustained delivery of plasmid DNA from polymeric scaffolds for tissue engineering. Adv Drug Deliv Rev 2006; 58: 500–14.
Response to Wang et al. comments on “Angiogenin, an angiogenic factor with potential for tissue engineering applications” We are pleased to read the comments of Wang et al. with considerable interest about our study in angiogenin in burn wound neovascularization. The authors found the stimulatory effect of angiogenin in promoting angiogenesis in artificial dermis. The report encourages us to explore its potential clinical role in burn wound healing. Angiogenin is a potent angiogenic factor that is originally isolated from the medium of colon cancer cells.1 The requirement of angiogenesis on cell growth implies a clear concept that the role of angiogenin on either malignant or nonmalignant conditions has now emerged. Although it remains immature, angiogenin measurement for diagnosis in some physiological or pathological conditions becomes possible. Burn fluid is a synthetic environment in which cells and growth factors are interlinked in the process of repair. Despite numerous angiogenic factors found in burn fluid, little progress has been known in the regulatory events involved in wound angiogenesis. Although the clinical value of differential angiogenin expression in burn blister fluids is uncertain, we have studied application of the levels for clinical assessment of a burn depth (unpublished data). Burn hypertrophy scar represents an undesirable end point of wound healing, where abnormal extracellular matrix accumulation and cellular activity result in thick, unsightly, and
Wound Rep Reg (2014) 22 288–289 © 2014 by the Wound Healing Society
symptomatic scar tissue. The presence of angiogenin in different cells further led some to suggest that angiogenesis may not be the sole biological function of angiogenin.2 We did find the angiogenin expression in scar fibroblast (unpublished data). The relationship between angiogenin and burn scar formation should be further studied. Shin-Chen Pan, MD, PhD; Haw-Yuan Chiu, MD, PhD Department of Surgery, Section of Plastic and Reconstructive Surgery, Institute of Clinical Medicine, National Cheng Kung University Medical College and Hospital, Tainan, Taiwan
REFERENCES 1. Fett JW, Strydom DJ, Lobb RR, Alderman EM, Bethune JL, Riordan JF, et al. Isolation and characterization of angiogenin, an angiogenic protein from human carcinoma cells. Biochemistry 1985; 24: 5480–6. 2. Moenner M, Gusse M, Hatzi E, Badet J. The widespread expression of angiogenin in different human cells suggests a biological function not only related to angiogenesis. Eur J Biochem 1994; 226: 483–90.
289
Angiogenin, an angiogenic factor with potential for tissue engineering applications
To the Editor: We read, with great interest, the serial articles published by Pan and colleagues.1,2 The authors describe that burn blister fluid contains large amounts of bioactive factors, and angiogenin (Ang) has been identified as the main component involved in the induction of early-stage neovascularization.1 The expression level of Ang in deep partial thickness burns is higher than that in superficial partial thickness burns. Ang alone was shown to be sufficient to induce endothelial differentiation of circulating angiogenic cells without the involvement of vascular endothelial growth factor A (VEGF-A).2 Such studies are encouraging and of major interest. Since our research team has been focusing on the applications of Ang in tissue engineering, we would like to introduce our understanding to Ang and angiogenesis. Angiogenesis represents a critical problem in tissue engineering that must be solved.3 Cytokines and growth factors, with the potential for angiogenic stimulation, play important roles in regulating the process of angiogenesis. To date, numerous angiogenic factors, e.g., VEGF, acidic and basic fibroblast growth factors (aFGF and bFGF, respectively), and epidermal growth factor (EGF), have been used to promote angiogenesis in conjunction with various delivery systems. Ang, first isolated from the serum-free supernatant of an established human adenocarcinoma cell line (HT-29),4 has been shown to play roles in tumorigenesis and angiogenesis.5 However, Ang is not a tumor-specific product; it is also expressed in normal cells and plasma.6,7 Ang is a normal constituent of the circulation and is present in the vasculature that rarely undergoes proliferation.8 Some groups suggested that Ang is a general requirement for cell proliferation and angiogenesis induced by various other angiogenic proteins, including VEGF, FGF, and EGF; inhibitors of the nuclear translocation of Ang were shown to abolish the angiogenic activities of these factors.9 Ang is the only member of the ribonuclease (RNase) superfamily with angiogenic activity and is also unique as the only angiogenic factor with RNase activity.4 Ang acts selectively on vascular endothelial cells (ECs) and smooth muscle cells (SMCs) to promote their proliferation, migration, and adhesion, inhibiting apoptosis, and to stimulate the ECs to form new vessels.10,11 Ang can also translocate into the nucleus where it acts as an RNase.12 Although the RNase activity of Ang is rather weak, it is critical due to its angiogenic properties. Ang is an important angiogenic factor in many physiological and pathological conditions. For example, the expression levels of Ang increase from 150 to 250 ng/mL between weeks 10 and 40 in the pregnancies.13 Pan et al. found the higher expression of Ang in the deep partial partial thickness burns.1 The angiogenic activity of Ang depends on its interaction with ECs and SMCs, as well as on its RNase activity, matrix 288
degradation, and participation in several signal transduction pathways.10 Although the angiogenic function of Ang has been confirmed,5 its potential applications in tissue engineering have seldom been discussed. Our research group began focusing on the role of Ang in early-stage angiogenesis. In previous work, a controlled Ang delivery system was established by heparinizing Ang into porous collagen-chitosan scaffolds; the results indicated that Ang was released from the heparinized scaffolds in a controlled manner, and the presence of Ang enhanced angiogenesis of the heparinized scaffold after subcutaneous implantation into rabbits.14 However, this type of protein delivery system may not be ideal because Ang proteins with very short half-lives in vivo may be denatured by the loading processes used to protect them from degradation and allow for prolonged release. Hence, further studies may employ gene-activated scaffolds to realize sustained delivery of Ang, thus promoting angiogenesis.15 To date, both Ang gene and protein, e.g., Ang plasmid DNA and recombinant human Ang protein, can be obtained easily. Various delivery systems have been constructed using physical or chemical methods. Of course, some other applications of Ang can also be developed. To sum up, this angiogenic factor has great potential to solve the angiogenesis insufficiency of tissueengineered constructs in the early stages.
ACKNOWLEDGMENTS This work was financially supported by the Natural Science Foundation of Zhejiang (LQ12H15001) and the Grand Science and Technology Special program of Zhejiang (2007C13040). Xingang Wang, PhD1; Yuanhai Zhang, BS2; Chunmao Han, PhD, MD1 1. Department of Burns & Wound Care Centre, Second Affiliated Hospital of Zhejiang University, Hangzhou and 2. Department of Burn and Plastic Surgery, Quhua Hospital, Quzhou, China
REFERENCES 1. Pan SC, Wu LW, Chen CL, Shieh SJ, Chiu HY. Deep partial thickness burn blister fluid promotes neovascularization in the early stage of burn wound healing. Wound Repair Regen 2010; 18: 311–18. 2. Pan SC, Wu LW, Chen CL, Shieh SJ, Chiu HY. Angiogenin expression in burn blister fluid: implications for its role in burn wound neovascularization. Wound Repair Regen 2012; 20: 731–9. Wound Rep Reg (2014) 22 288–289 © 2014 by the Wound Healing Society
Letters to the Editor
3. Novosel EC, Kleinhans C, Kluger PJ. Vascularization is the key challenge in tissue engineering. Adv Drug Deliv Rev 2011; 63: 300–11. 4. Fett JW, Strydom DJ, Lobb RR, Alderman EM, Bethune JL, Riordan JF, et al. Isolation and characterization of angiogenin, an angiogenic protein from human carcinoma cells. Biochemistry 1985; 24: 5480–6. 5. Xia WR, Fu WL, Cai L, Cai X, Wang YY, Zou MJ, et al. Expression, purification and characterization of recombinant human angiogenin in Pichia pastoris. Biosci Biotechnol Biochem 2012; 76: 1384–8. 6. Rybak SM, Fett JW, Yao QZ, Vallee BL. Angiogenin mRNA in human tumor and normal cells. Biochem Biophys Res Commun 1987; 146: 1240–8. 7. Shapiro R, Strydom DJ, Olson KA, Vallee BL. Isolation of angiogenin from normal human plasma. Biochemistry 1987; 26: 5141–6. 8. Tello-Montoliu A, Patel JV, Lip GY. Angiogenin: a review of the pathophysiology and potential clinical applications. J Thromb Haemost 2006; 4: 1864–74. 9. Kishimoto K, Liu S, Tsuji T, Olson KA, Hu GF. Endogenous angiogenin in endothelial cells is a general requirement for
10. 11.
12.
13.
14.
15.
cell proliferation and angiogenesis. Oncogene 2005; 24: 445– 56. Gao X, Xu Z. Mechanisms of action of angiogenin. Acta Biochim Biophys Sin (Shanghai) 2008; 40: 619–24. Bond MD, Vallee BL. Isolation and sequencing of mouse angiogenin DNA. Biochem Biophys Res Commun 1990; 171: 988–95. Shapiro R, Vallee BL. Human placental ribonuclease inhibitor abolishes both angiogenic and ribonucleolytic activities of angiogenin. Proc Natl Acad Sci U S A 1987; 84: 2238– 41. Eleftheriadis T, Kartsios C, Pissas G, Liakopoulos V, Antoniadi G, Galaktidou G, et al. Increased plasma angiogenin level is associated and may contribute to decreased T-cell zeta-chain expression in hemodialysis patients. Ther Apher Dial 2013; 17: 48–54. Shi H, Han C, Mao Z, Ma L, Gao C. Enhanced angiogenesis in porous collagen-chitosan scaffolds loaded with angiogenin. Tissue Eng Part A 2008; 14: 1775–85. Storrie H, Mooney DJ. Sustained delivery of plasmid DNA from polymeric scaffolds for tissue engineering. Adv Drug Deliv Rev 2006; 58: 500–14.
Response to Wang et al. comments on “Angiogenin, an angiogenic factor with potential for tissue engineering applications” We are pleased to read the comments of Wang et al. with considerable interest about our study in angiogenin in burn wound neovascularization. The authors found the stimulatory effect of angiogenin in promoting angiogenesis in artificial dermis. The report encourages us to explore its potential clinical role in burn wound healing. Angiogenin is a potent angiogenic factor that is originally isolated from the medium of colon cancer cells.1 The requirement of angiogenesis on cell growth implies a clear concept that the role of angiogenin on either malignant or nonmalignant conditions has now emerged. Although it remains immature, angiogenin measurement for diagnosis in some physiological or pathological conditions becomes possible. Burn fluid is a synthetic environment in which cells and growth factors are interlinked in the process of repair. Despite numerous angiogenic factors found in burn fluid, little progress has been known in the regulatory events involved in wound angiogenesis. Although the clinical value of differential angiogenin expression in burn blister fluids is uncertain, we have studied application of the levels for clinical assessment of a burn depth (unpublished data). Burn hypertrophy scar represents an undesirable end point of wound healing, where abnormal extracellular matrix accumulation and cellular activity result in thick, unsightly, and
Wound Rep Reg (2014) 22 288–289 © 2014 by the Wound Healing Society
symptomatic scar tissue. The presence of angiogenin in different cells further led some to suggest that angiogenesis may not be the sole biological function of angiogenin.2 We did find the angiogenin expression in scar fibroblast (unpublished data). The relationship between angiogenin and burn scar formation should be further studied. Shin-Chen Pan, MD, PhD; Haw-Yuan Chiu, MD, PhD Department of Surgery, Section of Plastic and Reconstructive Surgery, Institute of Clinical Medicine, National Cheng Kung University Medical College and Hospital, Tainan, Taiwan
REFERENCES 1. Fett JW, Strydom DJ, Lobb RR, Alderman EM, Bethune JL, Riordan JF, et al. Isolation and characterization of angiogenin, an angiogenic protein from human carcinoma cells. Biochemistry 1985; 24: 5480–6. 2. Moenner M, Gusse M, Hatzi E, Badet J. The widespread expression of angiogenin in different human cells suggests a biological function not only related to angiogenesis. Eur J Biochem 1994; 226: 483–90.
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