Quantitative analysis of pancreatic polypeptide cell distribution in the human pancreas

Abstract

The pancreatic islet is mainly composed of beta-, alpha- and delta-cells with small numbers of pancreatic polypeptide (PP) and epsilon cells. It is known that there is a region in the head of the pancreas that is rich in PP-cells. In the present study, we examined the distribution of PP-cells, and assessed the influence of the PP-cell rich region to quantify the total islet mass. Pancreatic tissues were collected from donors with no history of diabetes or pancreatic diseases (n = 12). A stereological approach with a computer-assisted large-scale analysis of whole pancreatic sections was applied to quantify the entire distribution of endocrine cells within a given section. The initial whole pancreas analysis showed that a PP-cell rich region was largely restricted to the uncinate process with a clear boundary. The distinct distribution of PP-cells includes irregularly shaped clusters composed solely of PP-cells. Furthermore, in the PP-cell rich region, beta- and alpha-cell mass is significantly reduced compared to surrounding PP-cell poor regions. The results suggest that the analysis of the head region should distinguish the PP-cell rich region, which is best examined separately. This study presents an important implication for the regional selection and interpretation of the results.

Figure 1. Whole pancreas analysis of the PP-cell distribution.

A: a. A pancreas from a 50-yr old male; S5). b. Collection scheme. Specimen divided into 66 consecutive sections, with preparation alternating between fresh-frozen (white) and paraffin embedding (grey). The latter set of tissue blocks was used in the present study. c. Representative view of the PP-cell rich region with irregularly shaped clusters of PP-cells. Immunostained for PP (red), insulin (green), glucagon (white) and nuclei (blue). d. PP-cell poor area. B: Regional distribution of PP-, beta-, and alpha-cell mass. C: a. Restricted PP-cell rich area illustrated in red. b. Deduced PP-cell rich region in vivo.

Figure 2. Detailed distribution of the PP-rich region in the head of the pancreas.

A: Virtual slice views of blocks in the head region. Immunostained for PP (red), insulin (green), glucagon (white) and nuclei (blue). All in the same scale. B: 3D visualization of islet size (area) and shape (circularity and Feret's diameter) distribution. Each dot represents a single islet/cluster. PP-cell containing clusters are shown in red. C: Quantitative analysis of individual islet size distribution and cellular composition. Relative frequency of islet size (gray bar) and ratios of beta (green), alpha (blue), and PP (red) cells within islets are plotted against islet size; means ± SEM.

Figure 3. Analysis on multiple specimens.

A: Inter-specimen comparison of endocrine cell mass in the head, body and tail region. B: a. Representative view of islets in the PP-cell rich area (PP in red, insulin in green, glucagon in white and nuclei in blue). b. Adjacent section immunostained for insulin (green), glucagon (red), somatostatin (white) and nuclei (blue). C: Intraspecimen comparison of the PP-cell rich and poor regions. a. A clear boundary between the PP-cell rich (area in the left) and poor region (right). b. Total endocrine cell area in each region. c. 3D plot of individual islet/cluster with PP-cell containing clusters in red. PP-cell rich (left) and poor area (right). d. Islet size distribution and cellular composition. PP-cell rich (left) and poor area (right).