Pancreatic expression of keratinocyte growth factor leads to differentiation of islet hepatocytes and proliferation of duct cells

Abstract

Keratinocyte growth factor, (KGF), a member of the fibroblast growth factor (FGF) family, is involved in wound healing. It also promotes the differentiation of many epithelial tissues and proliferation of epithelial cells as well as pancreatic duct cells. Additionally, many members of the highly homologous FGF family (including KGF), influence both growth and cellular morphology in the developing embryo. We have previously observed elevated levels of KGF in our interferon-gamma transgenic mouse model of pancreatic regeneration. To understand the role of KGF in pancreatic differentiation, we generated insulin promoter-regulated KGF transgenic mice. Remarkably, we have found that ectopic KGF expression resulted in the emergence of hepatocytes within the islets of Langerhans in the pancreas. Additionally, significant intra-islet duct cell proliferation in the pancreata of transgenic KGF mice was observed. The unexpected appearance of hepatocytes and proliferation of intra-islet duct cells in the pancreata of these mice evidently stemmed directly from local exposure to KGF.

Figure 1.

In situ hybridization indicates KGF mRNA expression is specific to pancreatic islets (A) and occurs near, but not in, ducts (B) of Ins-KGF of transgenic mice. The expression of KGF mRNA was tested using both antisense (A–C) and control sense (D) riboprobes. Original magnification, ×20 for all except A, which is ×10. Probes were prepared by in vitro transcription of a linearized plasmid containing KGF using [³⁵S]UTP as previously described. The result from a representative 10-week-old female mouse is shown.

Figure 2.

Morphological changes to islet structure in Ins-KGF mice. Shown are H&E-stained islets from Ins-KGF mice at 5 to 7 months of age; such changes are minor in younger mice (as in A, from a 6-week-old mouse). Original magnification, ×40. As the unique phenotype begins to develop (B; black arrowheads indicate islets containing a novel cell type shown at higher magnification in E and F) (7.5 months), the exocrine tissue remains typical as do many islets. Original magnification, ×4. Ins-KGF mice display distinct intra-islet ductal cell proliferation (C and D). Original magnification, ×32 and ×80, respectively. Additionally, extremely large cells with enlarged nuclei (E and F; see arrows) were observed at the peripheries of approximately one-fifth of the islets. Original magnification, ×32 and ×80, respectively.

Figure 3.

AFP and albumin staining identifies pancreatic hepatocytes within islets of Ins-KGF mice. Although AFP is not typically found within the normal adult pancreas (A, negative littermate control), it was strongly up-regulated in the large cells (B to D) first identified by H&E (see Figure 2 ▶ ). These cells were identified by their extremely large nuclei (C; see arrowhead) at the peripheries of islets (B; see arrowhead) or in trails extruding from islets (D). Although these large cells were not insulin positive (E; see arrowhead), they did express the liver protein, albumin (F). Original magnifications, ×40 (A), ×20 (B, D, and E), and ×80 (C and F).

Figure 4.

The islets of Ins-KGF transgenic mice (3-month-old female shown) have increased fibrosis in comparison with nontransgenic littermates as identified by trichrome stain. Fibrotic tissue appears blue, pancreatic hepatocytes are brilliant pink, typical islet cells are light pink, and acinar tissue is dark red. Fibrotic tissue separates areas of the islet containing hepatocytes seen on the right side of the photo from the typical cells of the islet on the left side. Original magnification, ×80.

Figure 5.

Increased proliferation within pancreata of Ins-KGF transgenic mice. A representative islet with intra-islet duct cells reveals proliferating cells staining brown, indicating that they have incorporated BrdU (male, five months). The cells in A (original magnification, ×20) can be seen in greater detail in the higher magnification of B (original magnification, ×40).