Leptin Receptor Ablation in Anterior Pituitary Somatotropes Reveals Broad Transcriptomic Changes and Sex-Specific Signaling Pathways

Anterior pituitary somatotropes utilize metabolic signals from the adipokine leptin to optimize responses to the body’s nutritional state via expression of growth hormone (GH), growth hormone releasing hormone receptors (GHRHR) and their transcriptional regulator POU1F1. To identify the mechanism underlying leptin action upon somatotropes, we analyzed single cell transcriptomes of pituitaries from somatotropes lacking leptin receptors (LEPR-null) compared with control pituitaries. Computational clustering of results identified all common pituitay cell types plus 5 undefined (UND) clusters. Differentially expressed genes (DEGs) (Log2FC0.58; adjusted p<0.055 thresholds) in mutant males revealed effects upon both transcriptional and mRNA translation regulators, but not direct effects upon hormone mRNA expression. Dysfunction in the male mutant LEPR-null somatotrope cluster was indicated by down-regulated genes in key transcriptional and second messenger signaling pathways, which were mostly upregulated in mutant females. Furthermore, mutant female somatotrope dysfunction was indicataed by an increase in markers for pituitary stem and/or progenitor cells (e.g.Sox9) and also increases (0.67-2.6-fold) in non-somatotrope hormone DEGs, e.g. Pomc, Lhb, Tshb, Cga, and/or Prl in female somatotrope, lactotrope, thyrotrope, corticotrope, and the UND3 clusters. Gh mRNA was decreased in mutant female somatotrope, UND2 and UND3 clusters. Collectively the increases in multihormonal expression did not coincide with increased expression of receptors for their releasing hormones. This and the presence of Sox9 suggested that the female somatotropes presented an immature gene signature. Collectively, these data point to a trophic role for leptin in the differentiation and/or maturation of somatotropes through regulatory pathways that are unique to each sex.