Endocrine Abstracts

Background: Functioning (FCA) and silent corticotroph (SCA) pituitary adenomas act differently from a clinical perspective, despite both subtypes showing positive ACTH staining by immunohistochemistry. They are challenging to treat, the former due to functional ACTH production and consequently hypercortisolemia leading to Cushing disease, whereas the latter due to invasive and recurrent behaviour. Moreover, the molecular mechanisms behind their distinct behaviour are not clear.

Aim: To investigate global transcriptome changes and identify signalling pathways that can explain FCA and SCA differences (e.g. hormone production vs. aggressive growth).

Material and methods: RNA sequencing was performed using Illumina HiSeq in 6 FCA (three women, five microadenomas) and 6 SCA (two women, all macroadenomas). Data was analysed using the tophat2- cufflinks-CummeRbund pipeline and the pathway enrichment analysis was performed using Pathview (https://pathview.uncc.edu). The candidate genes were evaluated by RT-qPCR in a larger cohort of adenomas (26 FCA and 10 SCA).

Results: By assessing the 631 differentially expressed genes (fold change (FC)>1.9, q<0.05), we identified eight signalling pathways to be enriched. Firstly, protein processing in endoplasmic reticulum (ER) (hsa04141) pathway was differentially regulated. Accordingly, FCA showed up-regulation of genes involved in ribosome anchor (RRBP1), glycosylation and folding process (RPN1, CALR, PDIA3, and UGGT2), protein recognition by luminal chaperones (HSPA5), and ER-associated degradation (HSPH1 and CRYAB), whereas the only gene to be up-regulated in SCA was EIF2AK2, a protein known to attenuate protein synthesis if activated. Secondly, five signalling pathways involved in cell adhesion (hsa04514, hsa04080, hsa04512, hsa04060, and hsa04510) were also differentially regulated. Of notice, the adenoma subtypes showed a distinct extracellular matrix profile with genes that were up-regulated in FCA (COL1A1, COL4A3, COL4A4, LAMA4 and NRCAM) and in SCA (COL2A1, CADM1, CNTN1, LAMC2, FN1, ITGB2, NECTIN3, NLGN1, PTPRC, SDC2, SPP1, SV2C and VTN). Lastly, two classical proliferation, growth, and survival pathways (MAPK – hsa04010, and PI3K-Akt – hsa04151) were differentially regulated, SCA showing, among other genes, higher levels of MAPK1 and SGK1 and lower DUSP4 gene expression.

Conclusion: Distinct clinical aspects of FCA and SCA may be explained by their different repertoires of activated signalling pathways, namely promoting growth in SCA and protein processing in FCA and their specific patterns of cell adhesion molecules. Further in vitro functional studies will be performed, in order to identify possible medical targets and to properly understand the involved mechanisms.