Amyloid formation results in recurrence of hyperglycaemia following transplantation of human IAPP transgenic mouse islets

Abstract

Aims/hypothesis: Islet transplantation is a potential cure for diabetes; however, rates of graft failure remain high. The aim of the present study was to determine whether amyloid deposition is associated with reduced beta cell volume in islet grafts and the recurrence of hyperglycaemia following islet transplantation.

Methods: We transplanted a streptozotocin-induced mouse model of diabetes with 100 islets from human IAPP (which encodes islet amyloid polypeptide) transgenic mice that have the propensity to form islet amyloid (n = 8-12) or from non-transgenic mice that do not develop amyloid (n = 6-10) in sets of studies that lasted 1 or 6 weeks.

Results: Plasma glucose levels before and for 1 week after transplantation were similar in mice that received transgenic or non-transgenic islets, and at that time amyloid was detected in all transgenic grafts and, as expected, in none of the non-transgenic grafts. However, over the 6 weeks following transplantation, plasma glucose levels increased in transgenic but remained stable in non-transgenic islet graft recipients (p < 0.05). At 6 weeks, amyloid was present in 92% of the transgenic grafts and in none of the non-transgenic grafts. Beta cell volume was reduced by 30% (p < 0.05), beta cell apoptosis was twofold higher (p < 0.05), and beta cell replication was reduced by 50% (p < 0.001) in transgenic vs non-transgenic grafts. In summary, amyloid deposition in islet grafts occurs prior to the recurrence of hyperglycaemia and its accumulation over time is associated with beta cell loss.

Conclusions/interpretation: Islet amyloid formation may explain, in part, the non-immune loss of beta cells and recurrence of hyperglycaemia following clinical islet transplantation.

Figure 1

Plasma glucose levels (panels a and b) and body weight (panels c and d) before and after streptozotocin-induced diabetes and after islet transplantation (TX) in mice that received 100 non-transgenic islets or 100 hIAPP transgenic islets and were followed for one week (panels a and c; non-transgenic: open circles, n=6; transgenic: solid circles, n=8) or for six weeks following islet transplantation (panels b and d; non-transgenic: open squares, n=10; transgenic: solid squares, n=12). Plasma glucose was similar in both studies for the first week after transplantation (panels a and b) and then increased gradually over six weeks following islet transplantation in mice that received transgenic islets (panel b). Body weight was similar between mice receiving transgenic or non-transgenic islets in both studies (panels c and d). * p<0.05 for mice transplanted with transgenic versus non-transgenic islets.

Figure 2

Representative sections of transplanted islet grafts under the kidney capsule stained for amyloid with thioflavin S (green) and insulin (red) (original magnification ×20). As expected, no amyloid was detected in non-transgenic islet grafts at one week (a) and six weeks (b) after transplantation. Amyloid deposits are present in transgenic islet grafts at one week (c) and six weeks (d) following transplantation.

Figure 3

Severity of amyloid deposition, beta cell volume, rate of beta cell apoptosis and rate of beta cell replication in non-transgenic and transgenic islet grafts at one week (a, c, e and g; non-transgenic: open bars, transgenic: solid bars) and six weeks (b, d, f and h; non-transgenic: open bars, transgenic: solid bars) post islet transplantation. Amyloid deposits were found in all eight transgenic grafts one week after islet transplantation (panel a) and were associated with lower beta cell volume (panel c), increased rate of beta cell apoptosis (panel e) and decreased rate of beta cell replication (panel g), although these did not reach statistical significance. Amyloid deposits were present in 11 of 12 transgenic islet grafts six weeks after islet transplantation (panel b) and were associated with a 30% reduction in beta cell volume (panel d), a two-fold higher rate of beta cell apoptosis (panel f) and a 50% decrease in beta cell replication (panel h), all of which were statistically significant. As expected, no amyloid was detected in any of the non-transgenic islet grafts at one week or six weeks post islet transplantation (panels a and b), as mouse IAPP is not amyloidogenic. * p<0.05; ** p<0.001; *** p<0.0001; for transgenic versus non-transgenic islet grafts.

Figure 4

Staining of apoptotic and replicating beta cells with TUNEL (a, c) and Ki-67 (b, d) in non-transgenic (a, b) and transgenic (c, d) islet grafts six weeks post transplantation (original magnification ×40). Arrows indicate apoptotic and replicating beta cells. Nuclear staining is in blue and insulin staining is in red (a, c) and green (b, d).

Figure 5

Long-term recurrence of hyperglycaemia as defined by plasma glucose levels >13.9 mmol/l occurred in 50% of mice that received transgenic (solid squares, n=12) but in none of the mice that received non-transgenic islets (open squares, n=10) over the six weeks following transplantation. * p=0.01 for mice transplanted with transgenic versus non-transgenic islets.