Impaired islet function with normal exocrine enzyme secretion is consistent across the head, body, and tail pancreas regions in type 1 diabetes

Abstract

Histopathological heterogeneity in human pancreas has been well documented; however, functional evidence at the tissue level is scarce. Herein we investigated in situ glucose-stimulated islet and carbachol-stimulated acinar cell secretion across the pancreas head (PH), body (PB), and tail (PT) regions in no diabetes (ND, n=15), single islet autoantibody-positive (1AAb+, n=7), and type 1 diabetes donors (T1D, <14 months duration, n=5). Insulin, glucagon, pancreatic amylase, lipase, and trypsinogen secretion along with 3D tissue morphometrical features were comparable across the regions in ND. In T1D, insulin secretion and beta-cell volume were significantly reduced within all regions, while glucagon and enzymes were unaltered. Beta-cell volume was lower despite normal insulin secretion in 1AAb+, resulting in increased volume-adjusted insulin secretion versus ND. Islet and acinar cell secretion in 1AAb+ were consistent across PH, PB and PT. This study supports low inter-regional variation in pancreas slice function and potentially, increased metabolic demand in 1AAb+.

Fig 1.. Similar islet and acinar cell secretion across the PH, PB and PT in the human ND pancreas

A & E. Insulin (A) and glucagon (E) secretion traces from slices of PH (teal), PB (purple), and PT (grey) shown as stimulation index calculated as fold of mean baseline (1G for insulin and 5.5G for glucagon). B-D. Quantification of insulin responses to 5.5G (B), 11.1G (C), and KCl (D) stimulation. F-I. Quantification of glucagon responses to 1G (F), 11.1G (G), 1G (H), KCl (I) stimulation. J-O. 3D morphometry of perifused slices showing slice volume (J), islet density (K), endocrine (L), insulin (M), and glucagon (N) volumes of perifused slices, and the contribution of insulin and glucagon volume to the total endocrine volume in perifused slices (O). P-R. Baseline pancreatic amylase (P), lipase (Q), and trypsinogen (R) release expressed as % of total enzyme content. S-U. Stimulated amylase (S), lipase (T), and trypsinogen (U) secretion in response to 10 μM carbachol expressed as stimulation index calculated as fold of baseline. N=15 ND donors for A-I, 7 ND donors for J-O, with 4 slices/region/donor and 14 ND donors for P-U with 5 slices/region/donor Dots represent individual donors, means are shown in black. Data are represented as mean ± SEM. Significance was assessed using RM one-way ANOVA of log-transformed data (B-D, F-I, J-N and P-U). *p < 0.05; **p < 0.01; ***p < 0.001; ****p < 0.0001; ns, not significant.

Fig 2.. Reduced insulin but not glucagon secretion in all pancreas regions in recent-onset T1D

A-C. Insulin secretion from slices of PH (A), PB (B), and PT (C) in slices from ND, 1AAb+, and T1D donors shown as absolute secreted amounts (mU/min). D-F. Insulin secretion traces from slices of PH (D), PB (E), and PT (F) in slices from ND, 1AAb+, and T1D donors shown as stimulation index calculated as fold of baseline (1G). G-I. Quantification of insulin responses to 5.5G (G), 11.1G (H), and KCl (I) stimulation. J-L. Glucagon secretion from slices of PH (J), PB (K), and PT (L) in slices from ND, 1AAb+, and T1D donors shown as absolute secreted amounts (pg/min). M-O. Glucagon secretion traces from slices of PH (M), PB (N), and PT (O) in slices from ND, 1AAb+, and T1D donors shown as stimulation index calculated as fold of baseline (5.5G). P-S. Quantification of glucagon responses to 1G (P), 11.1G (Q), 1G (R), and KCl (S) stimulation. N=15 ND, 7 1AAb+, and 5 T1D donors, with 4 slices/region/donor Dots represent individual donors. Data are represented as mean ± SEM. Significance was assessed using RM two-way ANOVA of log-transformed data (G-I and P-S). *p < 0.05; **p < 0.01; ***p < 0.001; ****p < 0.0001; ns, not significant. See also Figures S2 and S3.

Fig 3.. Preserved acinar cell function at T1D onset

A-C. Baseline pancreatic amylase (A), lipase (B), and trypsinogen (C) release in ND, 1AAb+, and T1D slices from the PH, PB, and PT, expressed as % of total enzyme content. D-F. Stimulated amylase (D), lipase (E), and trypsinogen (F) secretion in response to carbachol in ND, 1AAb+, and T1D slices from PH, PB, and PT, expressed as % of total enzyme content. G-I. Stimulated amylase (G), lipase (H), and trypsinogen (I) secretion in response to 10 μM carbachol in ND, 1AAb+, and T1D slices from PH, PB, and PT, expressed as stimulation index calculated as fold of baseline. N=14 ND, 7 1AAb+, and 5 T1D donors, with 5 slices/region/donor Dots represent individual donors. Data are represented as mean ± SEM. Significance was assessed using RM two-way ANOVA. *p < 0.05; **p < 0.01; ***p < 0.001; ****p < 0.0001; ns, not significant.

Fig 4.. Decreased endocrine and beta-cell mass across the pancreas at T1D onset

A-H. 3D morphometry of perifused slices showing slice volume (A), endocrine (B), insulin (C), and glucagon (D) volumes of perifused slices, islet density (E), and the contribution of insulin and glucagon volume to the total endocrine volume across the disease groups in PH (F), PB (G), and PT (H). I-K. Insulin secretion traces from slices of PH (I), PB (J), and PT (K) in slices from ND, 1AAb+, and T1D donors shown as secreted insulin normalized to beta-cell volume in the respective slices. L-O. Quantification of insulin responses to 1G (L), 5.5G (M), 11.1G (N), and KCl (O) stimulation. P-R. Glucagon secretion traces from slices of PH (P), PB (Q), and PT (R) in slices from ND, 1AAb+, and T1D donors shown as secreted glucagon normalized to alpha-cell volume in the respective slices. S-V. Quantification of glucagon responses to 5.5G (S), 1G (T), 11.1G (U), and 1G (V) stimulation. N=7 ND, 5 1AAb+, and 5 T1D donors, with 4 slices/region/donor Dots represent individual donors. Data are represented as mean ± SEM. Significance was assessed using RM two-way ANOVA of log-transformed data. *p < 0.05; **p < 0.01; ***p < 0.001; ****p < 0.0001; ns, not significant.