Human pancreatic acinar cell plasticity – potential for endocrine neogenesis?

Rodent pancreatic acinar cells retain differentiation plasticity in vitro and in vivo and showed reprogramming efficiency towards insulin-producing beta cells. In contrast, human pancreatic acinar cell plasticity was less well investigated. We found that acinar-to-ductal metaplasia and epithelial-to-mesenchymal transition occur when human acinar cells are cultured in 2D monolayer culture. In contrast, reprogramming towards an embryonic CD142+GP2+PDX1+SOX9+ cellular state can be appreciated in 3D suspension culture. Exocrine cells present at start of culture rearrange themselves as pancreatospheres, i.e. smooth spheroids composed of CA19.9+ duct-like and CD142+GP2+ embryonic-like cells. The acinar origin of the observed embryonic-like CD142+GP2+PDX1+SOX9+ cells was robustly confirmed by acinar-specific lineage tracing using FITC-conjugated UEA1 lectin, FACS sort, qRT-PCR and immunofluorescent analysis. Co-expression of CD142-GP2 surface markers and PDX1-SOX9 transcription factors were only observed during human foetal development (Ramond, C. et al. 2018). Furthermore, addition of Alk5iII, a TGF-beta signalling inhibitor, induced transition from a quiescent to an active proliferative state in the embryonic-like CD142+GP2+PDX1+SOX9+ cell population, i.e. 28-fold increased KI67 labelling. TGF-beta, Notch and BMP signalling pathways are involved in the differentiation of pancreatic progenitors towards endocrine cells as inhibition induced differentiation towards a beta-like cell phenotype (Rezania, A. et al. 2014). We observed, at day 4 of 3D suspension culture, increased phosphorylated Smad2 signalling in the pancreatospheres, which was abrogated by the addition of Alk5iII. Inhibition of the Notch signalling, by addition of the gamma secretase inhibitor compound E, inhibited the proliferative effect of Alk5iII indicating activated Notch signalling in the TGF-beta inhibitor condition. Furthermore, Notch inhibition induced increased BMP2 transcription. This indicates an interplay between TGF-beta, Notch and BMP in the 3D-cultured exocrine fraction. It remains to be demonstrated whether manipulation of these signalling pathways can induce “chemical” reprogramming of acinar cells to endocrine cells.