👤 Serena Avallone

Acromegaly, primarily caused by GH-secreting pituitary neuroendocrine tumors (GH-PitNETs), in about half of cases exhibits resistance to somatostatin receptor ligands (SRLs), making surgery the primary treatment. Recent evidence suggests that glucose-dependent insulinotropic polypeptide receptor (GIPR) overexpression in a subset of GH-PitNETs contributes to disease heterogeneity, particularly in tumors showing a paradoxical GH rise after glucose load, which are associated with a less aggressive phenotype and better first-generation SRLs response. This study investigated the functional role of GIPR in somatotroph cells by generating stable human GIPR-expressing GH3 cells (GH3hGIPR) and comparing them with empty vector controls. Functional assays demonstrated that GIPR activation induces cAMP/PKA and MAPK/ERK signaling, enhances GH and prolactin secretion, and increases intracellular calcium oscillations, dependent on extracellular calcium influx. Transcriptomic analysis revealed differential gene expression patterns linked to cell motility, neuronal development, and extracellular matrix remodeling in GH3hGIPR cells, aligning with clinical observations in GIPR+ tumors. However, GIPR overexpression did not alter cell proliferation or viability, suggesting that its role in tumor behavior may depend on additional molecular or epigenetic factors. These findings highlight the importance of GIPR signaling in somatotroph cell function and its potential influence on therapeutic responses, though further studies are needed to clarify its contribution to tumorigenesis and SRL sensitivity. Show less

A paradoxical increase of growth hormone (GH) following oral glucose load has been described in ∼30% of patients with acromegaly and has been related to the ectopic expression of the glucose-dependent insulinotropic polypeptide (GIP) receptor (GIPR) in somatotropinomas. Recently, we identified germline pathogenic variants and somatic loss of heterozygosity of lysine demethylase 1A (KDM1A) in patients with GIP-dependent primary bilateral macronodular adrenal hyperplasia with Cushing's syndrome. The ectopic expression of GIPR in both adrenal and pituitary lesions suggests a common molecular mechanism. We aimed to analyze KDM1A gene sequence and KDM1A and GIPR expressions in somatotroph pituitary adenomas. We conducted a cohort study at university hospitals in France and in Italy. We collected pituitary adenoma specimens from acromegalic patients who had undergone pituitary surgery. We performed targeted exome sequencing (gene panel analysis) and array-comparative genomic hybridization on somatic DNA derived from adenomas and performed droplet digital PCR on adenoma samples to quantify KDM1A and GIPR expressions. One hundred and forty-six patients with sporadic acromegaly were studied; 72.6% presented unsuppressed classical GH response, whereas 27.4% displayed a paradoxical rise in GH after oral glucose load. We did not identify any pathogenic variant in the KDM1A gene in the adenomas of these patients. However, we identified a recurrent 1p deletion encompassing the KDM1A locus in 29 adenomas and observed a higher prevalence of paradoxical GH rise (P = .0166), lower KDM1A expression (4.47 ± 2.49 vs 8.56 ± 5.62, P < .0001), and higher GIPR expression (1.09 ± 0.92 vs 0.43 ± 0.51, P = .0012) in adenomas from patients with KDM1A haploinsufficiency compared with those with 2 KDM1A copies. Unlike in GIP-dependent primary bilateral macronodular adrenal hyperplasia, KDM1A genetic variations are not the cause of GIPR expression in somatotroph pituitary adenomas. Recurrent KDM1A haploinsufficiency, more frequently observed in GIPR-expressing adenomas, could be responsible for decreased KDM1A function resulting in transcriptional derepression on the GIPR locus. Show less