Effects of diabetes and hypoxia on gene markers of angiogenesis (HGF, cMET, uPA and uPAR, TGF-alpha, TGF-beta, bFGF and Vimentin) in cultured and transplanted rat islets

AIMS/HYPOTHESIS

The vascularisation of newly transplanted islets originates from the recipients. Because islets transplanted into a diabetic do less well than those transplanted into a euglycaemic environment, we examined the hypothesis that gene expression of angiogenic factors in grafts is delayed in diabetes. These factors include hepatocyte growth factor (HGF) and its receptor c-MET, and urokinase plasminogen activator (uPA) and its receptor uPAR, basic fibroblast growth factor (bFGF), TGF-alpha and TGF beta-1.

METHODS

Isolated rat islets were studied in vitro under normoxic and hypoxic culture conditions and gene expression was determined with semi-quantitative multiplex RT-PCR. We found that HGF but not c-MET expression was induced by hypoxia in vitro. Using syngeneic Lewis rats, gene expression was also studied in grafts on days 1, 3, 5, 7 and 14 after transplantation.

RESULTS

In grafts of normoglycaemic rats, HGF expression was enhanced on day 3 and maintained whereas expression of c-MET fell and remained down until day 14. Expression of uPA was up at day 3 and remained high; expression of uPAR was also up at day 3 but then fell to control levels at day 14. Expression of bFGF, TGF-alpha and TGF beta-1 persisted throughout. Vimentin, a marker of fibroblasts, had increased expression at day 1 which was further enhanced in subsequent days. In the grafts of diabetic recipients the expression of HGF, uPA and uPAR were delayed, being clearly expressed at day 5 rather than day 3. Vimentin expression was similarly delayed.

CONCLUSION/INTERPRETATION

This apparent delay in angiogenesis provides a potential mechanism for the less favourable outcomes of islets transplanted into diabetic recipients.

The homeodomain protein IDX-1 increases after an early burst of proliferation during pancreatic regeneration

Islet duodenal homeobox 1 (IDX-1/PF-1/STF-1/PDX-1), a homeodomain protein that transactivates the insulin promoter, has been shown by targeted gene ablation to be required for pancreatic development. After 90% pancreatectomy (Px), the adult pancreas regenerates in a process recapitulating embryonic development, starting with a burst of proliferation in the epithelium of the common pancreatic duct. In this model, IDX-1 mRNA was detected by semiquantitative reverse transcription-polymerase chain reaction in total RNA from isolated common pancreatic ducts at levels 10% of those of isolated islets. The IDX-1 mRNA levels were not significantly different for common pancreatic ducts of Px, sham Px, and unoperated rats and did not change with time after surgery. By immunoblot analysis, IDX-1 protein was only faintly detected in these ducts 1 and 7 days after Px or sham Px but was easily detected at 2 and 3 days after Px. Similarly, IDX-1 immunostaining was barely detectable in sham or unoperated ducts but was strong in ducts at 2-3 days after Px. The increase of IDX-1 immunostaining followed that of BrdU incorporation (proliferation). These results indicate a posttranscriptional regulation of the IDX-1 expression in ducts. In addition, islets isolated 3-7 d after Px showed higher IDX-1 protein expression than control islets. Thus, in pancreatic regeneration IDX-1 is upregulated in newly divided ductal cells as well as in islets. The timing of enhanced expression of IDX-1 implies that IDX-1 is not important in the initiation of regeneration but may be involved in the differentiation of ductal cells to beta-cells.

Internal calvarial bone distraction in rabbits with experimental coronal suture immobilization: effects of overdistraction

This study was designed to assess the effects of overdistraction of an experimentally immobilized coronal suture using an internal appliance on craniofacial growth in rabbits. Fifty-three, 1.5-week-old rabbits were used. Markers were placed on either side of the calvarial sutures. Thirty-nine rabbits had bilateral coronal suture immobilization using methyl methacrylate; 14 rabbits served as normal controls. At 6 weeks of age, the 39 immobilized rabbits were randomly assigned to four groups: (1) immobilized controls (n = 14); (2) suturectomy (n = 6); (3) suturectomy with distraction (n = 9); and (4) suturectomy with overdistraction (n = 10). Lateral head radiographs were taken at 1.5, 6, 12, and 18 weeks of age. Results revealed that, by 18 weeks of age, rabbits with overdistraction exhibited significant compensatory growth abnormalities in the cranial vault, midface, and anterior cranial base compared with the other groups. Results indicate that overdistraction may contribute to craniofacial anomalies through altered growth vectors and compressive tension-stress forces at adjacent sutures and suggest that it may be important to keep "pace" with the growing coronal suture and neurocapsular matrix during distraction to reestablish normal craniofacial morphology.