GTMB 7 - Gene Therapy & Molecular Biology

More documents

Recommendations

Info

Zhang et al: Angiogenic Gene Therapy for Improving Islet Graft Vascularizationand stability of the newly formed blood vessels. These twofactors act synergistically to ensure new blood vesselformation, growth and maturation.VEGF has four different isoforms in humans,consisting of 121, 165, 189 and 206 amino acid residues,all of which are generated by alternative splicing of asingle gene. Rodents have only three isoforms, namelyVEGF120, VEGF164 and VEGF188, each polypeptideone amino acid shorter than their corresponding humanhomologues (Kim et al, 2000; Vasir et al, 2000, 2001).The most abundant and widely distributed form isVEGF165 in humans (or VEGF164 in rodents). In concertwith their respective functions in angiogenesis /vasculogenesis, the receptors for both VEGF (VEGFR-1/Flt1 and VEGFR-2/Flk-1/KDR) and Ang-1 (Tie2) areselectively expressed in the vascular endothelium (Ferraraand Davis-Smyth, 1997; Otani et al, 1999; Kim et al,2000). In addition, both VEGF and Ang-1 are expressed inthe pancreas, suggesting their functional importance inpancreatic tissue angiogenesis / vasculogenesis (Vasir etal, 2001). However, due to limited data in the literature,little is known about the functional interplay betweenVEGF and Ang-1 in islet revascularization posttransplantation.c. Genes involved in islet revascularizationOf the genes whose functions are involved inangiogenesis, VEGF seems to play a crucial role in isletrevascularization. Recent studies by Vasir and colleagues(2000, 2001) indicate that VEGF expression in islet cellsis transiently induced, followed by significant decline twothreedays post transplantation. This impaired expressionof VEGF is further pronounced in the presence ofprevailing hyperglycemia, which coincides with delayedexpression profiles of VEGF receptor molecules, Flk-1/KDR and Flt-1, in islet grafts post transplantation indiabetic animals (Hellerstrom et al, 1898; Korsgren andJansson, 1989; Mattson et al, 2002). These results reflectto some extent an impaired angiogenesis of islet grafts inthe diabetic milieu, which is contributable to the lack ofadequate islet revascularization under hyperglycemicconditions.In addition to VEGF, there are a number of otherangiogenic molecules whose expression in islet cells alsoseems to affect islet revascularization, including fibroblastgrowth factor (FGF), hepatic growth factor (or scatterfactor) (HGF/SF) and its receptor c-Met, transforminggrowth factor-α (TGF-α) and -β (TGF-β), and urokinaseplasminogen activator (uPA) and its receptor uPAR. LikeVEGF, FGF appears to be a positive regulator ofangiogenesis, as it has been shown to induce endothelialcell proliferation, migration and angiogenesis (Bikfalvi etal, 1997; Vasir et al, 2000, 2001, Kawakami et al, 2001).Regarding the function of TGF in angiogenesis, TGF-αhas been shown to stimulate the growth of microvascularendothelial cells (Tokuda et al, 2003). In addition, TGF-αis also a potent inducer of VEGF (Gille et al, 1997; Li etal, 2003). On the other hand, TGF-β is found to stimulatewound healing and regulate differentiation of certain celltypes (Chegini, 1997; Asplin et al, 2001; Li et al, 2003).Although FGF and TGF have been implicated to playimportant roles in angiogenesis (Vasir et al, 2000;Kawakami et al, 2001), their functional contributions toislet revascularization remain unknown.HGF/SF is a mitogen that acts to stimulate celldivision and proliferation of a variety of cell types,including smooth muscle cells and pericytes that arefunctionally involved in blood vessel formation (Bussolinoet al, 1992; Ahmet et al, 2003; Ding et al, 2003; Senguptaet al, 2003). In addition, it has recently been shown thatelevated HGF production in islet grafts significantlyimproves the outcome of marginal islet transplantation dueto its proliferative effect on islet cells (Garcia-Ocana et al,2003). c-Met is a tyrosine kinase receptor of HGF/SF,which is expressed in endothelial cells. In concert with theaction of HGF/SF, the islet-specific expression of c-Metfunctions to mediate the mitogenic effect of HGF/SF onislet cell growth and proliferation (Weidner et al, 1993;Rosen et al, 1997). Vasir and colleagues (2000) showedthat the expression of HGF/SF together with its receptor innewly transplanted islets is profoundly delayed in diabeticanimals (Laing et al, 2003), which correlates with reducedislet graft vascularization. Nevertheless, its specific role inislet revascularization has not been defined.The urokinase plasminogen activator system,consisting of uPA and uPAR, plays a pivotal role inangiogenic sprouting. uPA binds to its cell surfacereceptor uPAR and converts plasminogen to plasmin, aserine protease with a broad specificity that functions tocatalyze the degradation of extracellular matrix/basementmembrane, an essential process that is required forclearing a path to facilitate endothelial cell migration andtissue remodeling in an angiogenic cascade (Saksela andRifkin, 1988; Bacharach et al, 1992; Pepper et al, 1993).Consistent with their roles in angiogenesis, both uPA anduPAR expression are stimulated by VEGF and HGF/SF(Pepper et al, 1992; Mandriota et al, 1995). Like otherangiogenic molecules, the expression of uPA and uPAR innewly engrafted islets is significantly delayed (Vasir et al,2000). It has been suggested that impaired uPA and uPARexpression in newly transplanted islets also contributes toinsufficient islet revascularization under diabeticconditions.4. Factors affecting islet revascularizationAs discussed above, islet revascularization is animportant determinant for the clinical outcome of islettransplantation. Unfortunately, transplanted islets areinvariably associated with markedly reducedrevascularization no matter whether islets are transplantedin the renal, splenic or hepatic subcapsular space (Janssonand Carlsson, 2002). What are the factors that adverselyaffect islet revascularization?.One potential factor that affects isletrevascularization is the presence of prevailinghyperglycemia in diabetic recipients. Data in support ofthis view have been obtained by Vasir et al. (2000, 2001),who showed that the expression of several key angiogenic156
Gene Therapy and Molecular Biology Vol 7, page 157proteins and their respective receptor molecules in newlyengrafted islets is significantly delayed in diabeticrecipient mice, compared to that in nondiabetic recipientmice. These results suggest that islets transplanted underthe renal capsule in a diabetic environment fare less wellin terms of graft vascularization than those transplanted ina normoglycemic subject. In contrast, a different view ofthe possible impact of prevailing hyperglycemia on isletrevascularization is provided by Menger et al, (1992), whoshowed that the relative microvascular blood perfusion isequivalent in islets engrafted in the striated skin muscle inhyperglycemic and normoglycemic Syrian goldenhamsters. Unfortunately, there is no quantitative dataregarding the functional vascular density in islet grafts inrelation to the presence or absence of persistenthyperglycemia provided in these studies. Thus, whetherand to what extent prevailing hyperglycemia affects isletrevascularization still remain an issue of debate.A second factor that may potentially influence isletrevascularization is the use of immunosuppressive agentsassociated with islet transplantation. One outstandingconcern is that immunosuppressive agents are commonlyassociated with anti-proliferative activity and their clinicalapplication in conjunction with islet transplantation mayadversely affect islet revascularization. Theimmunosuppressants, sirolimus and tacrolimus, are shownto inhibit angiogenesis in a dose-dependent manner in bothin vitro and in vivo angiogenesis assays (Eckhard et al,2003). In the same sensitive assays, cyclosporine andprednisolone are also found to retain anti-angiogenicactivities in counteracting the proliferative effect of FGFin angiogenesis (Eckhard et al, 2003), although it has beenpreviously reported that the application of cyclosporin-Adoes not seem to alter microvascular perfusion to isletgrafts (Mendola et al, 1997; Vajkoczy et al, 1999). Theseresults raise a great deal of concern that clinicalapplication of immunosuppressive drugs, which isintended to prevent islet graft loss, may actuallycompromise the viability of newly transplanted islets byhampering the process of islet revascularization.A third limiting factor for islet revascularization isthe presence of contaminating exocrine cells in isolatedislets, including macrophage, dendritic cells (DC) andendothelial cells. It has been suggested that exocrine cellsperturb angiogenesis and islet revascularization (Heuser etal, 2000; Jansson and Carlsson, 2002). Consistent with thisidea is the observation that culturing of islets prior totransplantation tends to improve the outcome of islettransplantation, as culturing helps eliminate contaminatingcells, in particular, the antigen presenting cells (APC) inislet preparation (Gaber et al, 2001; Kuttler et al, 2002).However, culturing of freshly isolated islets also results inthe loss of endothelium in islets. Interestingly, recentstudies show that intra-islet endothelial cells serve asintegrated components in angiogenesis and functiontogether with recipient endothelium to facilitate the overallislet graft vascularization (Brissova et al, 2003; Linn et al,2003). These results suggest that transplantation of freshlyisolated islets may be favorable for islet viability becauseof the functional contribution of intra-islet endothelialcells to islet revascularization post transplantation(Jansson and Carlsson, 2002).Finally, a less well-characterized factor that mightaffect islet revascularization is islet cryopreservation. Thisprocess is necessary as it can afford a great deal offlexibility and additional advantages to clinical islettransplantation. Cryopreservation allows pooling ofmarginal islets and subsequent distribution of islets todifferent islet transplantation centers/hospitals. It alsoallows sufficient time for pre-transplantation qualitycontrol testing of isolated islets to ensure islet cell viabilityand microbiological sterility prior to transplantation. Inaddition, cryopreservation also allows for geneticmodification of islets by introducing angiogenic,cytoprotective or immunomodulatory genes via genetransfer to islets prior to islet transplantation to improvethe clinical outcome of islet transplantation in the future.However, recovery of functional islets aftercryopreservation has been technically challenging, asfreezing and thawing can significantly reduce the viabilityof islet cells (Kuo et al, 2002). Up to 50% of functionalislet loss has been reported after cryopreservation (Lakeyet al, 2001). Furthermore, the extent to whichcryopreservation affects islet revascularization remains tobe determined.B. Enhancing islet revascularization1. Angiogenic gene transfer to enhance isletrevascularizationAs discussed above, rapid and sufficient isletrevascularization is crucial for long-term survival andfunction of islet grafts post transplantation. Delayed andinadequate revascularization of newly transplanted isletscan deprive islet cells of oxygen and nutrients, resulting inislet cell death and premature graft failure. Given the factthat successful islet transplantation depends on theinfusion of sufficiently large amounts of islets, whichusually requires at least two cadaveric pancreata perrecipient, increased islet revascularization is expected toreduce the number of islets and improve the pancreasdonor to recipient ratio required for transplantation. Inaddition, rapid and adequate islet revascularization willprotect islet grafts from hypoxia-induced inflammationand necrosis, thereby improving long-term graft survivaland providing better preservation of functional islet mass.However, only limited efforts have been made in the pastin this aspect of islet transplantation.VEGF is known to play a pivotal role inangiogenesis / vasculogenesis. To investigate itsangiogenic effect on islet revascularization, Sigrist andcolleagues (2002) have applied collagen-immobilizedVEGF protein in encapsulated islets, followed bytransplantation into the peritoneal cavity of streptozotocininduceddiabetic mice. Blood glucose and plasma insulinlevels were determined and animals were sacrificed twoweeks post transplantation. It was found that isletstransplanted in the presence of collagen-immobilizedVEGF protein show significantly increased angiogenesisand microvasculature in islet grafts, which associated withincreased insulin production and improved glycemic157
Page 7 and 8:
Instructions to authors:Gene Therap
Page 9:
Please submit an electronic version
Page 12:
103-111 ResearchArticle113-133 Revi
Page 17 and 18:
Gene Therapy and Molecular Biology
Page 19 and 20:
Page 21 and 22:
Page 23 and 24:
Page 25 and 26:
Page 27 and 28:
Page 29 and 30:
Page 31 and 32:
Page 33 and 34:
Page 35 and 36:
Page 37 and 38:
Page 39 and 40:
Page 41 and 42:
Page 43 and 44:
Page 45 and 46:
Page 47 and 48:
Page 49 and 50:
Page 51 and 52:
Page 53 and 54:
Page 55 and 56:
Page 57 and 58:
Page 59 and 60:
Page 61 and 62:
Page 63 and 64:
Page 65 and 66:
Page 67 and 68:
Page 69 and 70:
Page 71 and 72:
Page 73 and 74:
Page 75 and 76:
Page 77:
Page 80 and 81:
Epperly et al: Late injection of Mn
Page 82 and 83:
Epperly et al: Late injection of Mn
Page 84 and 85:
Goldberg-Cohen et al: Regulation of
Page 86 and 87:
Page 88 and 89:
Page 90 and 91:
Gascón-Irún et al: Gene therapy a
Page 92 and 93:
Page 94 and 95:
Page 96 and 97:
Page 98 and 99:
Page 100 and 101:
Page 102 and 103:
Page 104 and 105:
Page 106 and 107:
Suzuki et al: Regulation of the Sp/
Page 108 and 109:
Page 110 and 111:
Page 112 and 113:
Page 114 and 115:
Li et al: MET amplification in live
Page 116 and 117:
Li et al: MET amplification in live
Page 118 and 119:
Chavakis et al: Leukocyte adhesion
Page 120 and 121: Chavakis et al: Leukocyte adhesion
Page 128 and 129: Sanlioglu et al: Adenovirus mediate
Page 150 and 151: George et al: Gene therapy for vasc
Page 168 and 169: Zhang et al: Angiogenic Gene Therap
Page 182 and 183: Xu et al: G-CSF receptor-mediated S
Page 188 and 189: Burek et al: Calcium induced cell d
Page 196 and 197: David et al: Current status and fut
Page 220 and 221:
David et al: Current status and fut
Page 222 and 223:
Page 224 and 225:
Page 226 and 227:
Stoll et al: The role of EBV and ge
Page 228 and 229:
Page 230 and 231:
Page 232 and 233:
Page 234 and 235:
Page 236 and 237:
Maruyama et al: Kidney-targeted pla
Page 238 and 239:
Page 240 and 241:
Page 242 and 243:
Page 244 and 245:
Kren et al: Hepatocyte-targeted del
Page 246 and 247:
Page 248 and 249:
Page 250 and 251:
Page 252 and 253:
Page 254 and 255:
Zeng: PRL-3 as a target for cancer
Page 256 and 257:
Page 258 and 259:
Page 260 and 261:
Latchman: Protective effect of heat
Page 262 and 263:
Page 264 and 265:
Page 266 and 267:
Page 268 and 269:
Page 270 and 271:
Cai et al: Lung cancer gene therapy
Page 272 and 273:
Page 274 and 275:
Page 276 and 277:
Page 278 and 279:
Page 280:
Page 283 and 284:
Page 285 and 286:
Page 287 and 288:
Page 289 and 290:
Page 291 and 292:
Page 293 and 294:
Page 295 and 296:
Page 297 and 298:
Page 299 and 300:
Page 301 and 302:
Page 303 and 304:
Page 305 and 306:
Page 307 and 308:
Page 309:
show all

GTMB 7 - Gene Therapy & Molecular Biology

You also want an ePaper? Increase the reach of your titles

Delete template?

Save as template?