Michael J. Shipston

The regulation of electrical excitability of anterior pituitary corticotrophs is critical for an appropriate response of the hypothalamic‐pituitary‐adrenal (HPA) axis in the face of diverse physiological challenges in health and disease. However ion channels that control corticotroph excitability remain poorly characterised. Members of the mammalian ether‐à‐go‐go (EAG) channel family are voltage‐gated potassium channels with diverse functions in the endocrine, cardiovascular and nervous systems. Expression of Kcnh2 mRNA, which encodes for the Eag‐related potassium channel Erg1, is enriched in the anterior pituitary although its functional role is poorly understood in native anterior pituitary cells. We reveal that Kcnh2 is the major Eag‐channel family member mRNA expressed in male and female murine corticotrophs. Patch clamp electrophysiological analysis revealed corticotrophs exhibit robust Erg‐like currents that are inhibited by the selective Erg‐inhibitor E4031 but are not regulated by the major hypothalamic secretagogues, corticotrophin releasing hormone (CRH) or arginine vasopressin (AVP), that increase corticotroph excitability. Pharmacological inhibition of Erg currents had no effect on spontaneous electrical excitability in corticotrophs. Rather, paradoxically, Erg currents were important for supporting CRH‐induced bursting, similar to the role of large‐conductance calcium‐ and voltage‐activated potassium (BK) channels, providing a level of redundancy to control bursting. Indeed mathematical modelling revealed that in the absence of BK channels CRH‐induced bursting can be supported in thepresence of Erg current. We thus reveal a novel role for Erg‐like channels in controlling CRH‐induced bursting in murine anterior pituitary corticotrophs that is likely to be an important determinant of HPA axis regulation in health and disease. image Key points: Voltage‐gated ether‐à‐go‐go‐related (Erg) potassium channels are key determinants of cellular excitability; however their functional role in native anterior pituitary cells remains poorly understood. Male and female murine corticotrophs predominantly express Kcnh2 (Erg1) mRNA, and electrophysiological recordings reveal functional Erg‐like potassium currents sensitive to the Erg inhibitor E4031. Erg currents do not control the basal electrical excitability of corticotrophs. We reveal a novel role for Erg currents in supporting electrical bursting in corticotrophs induced by the hypothalamic secretagogue, corticotrophin releasing hormone (CRH). Bursting in corticotrophs can be supported by both Erg and BK channels revealing a level of redundancy to the CRH response that will be critical for understanding the role of Erg channels in control of the stress axis in health and disease.

A large body of evidence has shown that corticotrophs, the anterior pituitary cells central to the generation of hormonal stress responses, exhibit heterogeneous functional behavior, suggesting the presence of functional sub-populations of corticotrophs. We investigated whether this was the case at the transcriptomic level by conducting a comprehensive analysis of scRNA-seq datasets from rodent pituitary cells. We envisaged two alternative scenarios, one where robust subtypes of corticotrophs exist, and the other where these subpopulations were only transient states, possibly transitioning into one another. Our findings suggest that corticotrophs transition between multiple transcriptional states rather than existing as rigidly defined subpopulations. We employed marker gene-based comparisons and whole transcriptome label transfer approaches to analyze transcriptional signatures across datasets. Marker-based clustering revealed strikingly low similarity in the identified subpopulations across datasets. This analysis evidenced the presence of transcriptional states with different functional relevance, related to different stages of hormonal signalling. Similarly, the label transfer approach, which considers non-linear interactions across the entire transcriptome showed that transcriptional states could be detected across independent datasets. This classification relied on broader gene expression patterns rather than conventional marker genes, reinforcing the notion of continuous rather than discrete cell states. Furthermore, trajectory analysis by RNA velocity indicated dynamic transitions between transcriptional states, suggesting the presence of transcriptional mechanisms facilitating rapid recruitment of corticotrophs in response to physiological demands.Our findings align with evidence from other endocrine cell types, such as lactotrophs and pancreatic β-cells, where hormone secretion is linked to fluctuating transcriptional activity. The observed transitions in corticotroph states suggest a mechanism allowing flexible hormonal responses to unpredictable and time-varying stressful events. Additionally, this study highlights the challenges associated with scRNA-seq methodologies, including data sparsity, batch effects, and pseudoreplication, underscoring the need for rigorous experimental design and reproducibility in single-cell transcriptomics research. These insights contribute to a broader understanding of pituitary cell plasticity and endocrine adaptation mechanisms.

A major challenge in the stem cell biology field is the ability to produce fully functional cells from induced pluripotent stem cells (iPSCs) that are a valuable resource for cell therapy, drug screening, and disease modelling. Here, we developed a novel inducible CRISPR-mediated activation strategy (iCRISPRa) to drive the expression of multiple endogenous transcription factors (TFs) important for in vitro cell fate and differentiation of iPSCs to haematopoietic progenitor cells. This work has identified a key role for IGFBP2 in developing haematopoietic progenitors. We first identified nine candidate TFs that we predicted to be involved in blood cell emergence during development, then generated tagged gRNAs directed to the transcriptional start site of these TFs that could also be detected during single-cell RNA sequencing (scRNAseq). iCRISPRa activation of these endogenous TFs resulted in a significant expansion of arterial-fated endothelial cells expressing high levels of IGFBP2, and our analysis indicated that IGFBP2 is involved in the remodelling of metabolic activity during in vitro endothelial to haematopoietic transition. As well as providing fundamental new insights into the mechanisms of haematopoietic differentiation, the broader applicability of iCRISPRa provides a valuable tool for studying dynamic processes in development and for recapitulating abnormal phenotypes characterised by ectopic activation of specific endogenous gene expression in a wide range of systems.

Chronic stress results in long-term dynamic changes at multiple levels of the hypothalamic-pituitary-adrenal (HPA) axis resulting in stress axis dysregulation with long-term impacts on human and animal health. However, the underlying mechanisms and dynamics of altered of HPA axis function, in particular at the level of pituitary corticotrophs, during a period of chronic stress and in the weeks after its cessation (defined as “recovery”) are very poorly understood. Here, we address the fundamental question of how a period of chronic stress results in altered anterior pituitary corticotroph function and whether this persists in recovery, as well as the transcriptomic changes underlying this. We demonstrate that, in mice, spontaneous and corticotrophin-releasing hormone-stimulated electrical excitability of corticotrophs, essential for ACTH secretion, is suppressed for weeks to months of recovery following a period of chronic stress. Surprisingly, there are only modest changes in the corticotroph transcriptome during the period of stress, but major alterations occur in recovery. Importantly, although transcriptional changes for a large proportion of mRNAs follow the time course suppression of corticotroph excitability, many other genes display highly dynamic transcriptional changes with distinct time courses throughout recovery. Taken together, this suggests that chronic stress results in complex dynamic transcriptional and functional changes in corticotroph physiology, which are highly dynamic for weeks following cessation of chronic stress. These insights provide a fundamental new framework to further understand underlying molecular mechanisms as well approaches to both diagnosis and treatment of stress-related dysfunction of the HPA axis.

The hypoxic ventilatory response (HVR) is critical to breathing and thus oxygen supply to the body and is primarily mediated by the carotid bodies. Here we reveal that carotid body afferent discharge during hypoxia and hypercapnia is determined by the expression of Liver Kinase B1 (LKB1), the principal kinase that activates the AMP-activated protein kinase (AMPK) during metabolic stresses. Conversely, conditional deletion in catecholaminergic cells of AMPK had no effect on carotid body responses to hypoxia or hypercapnia. By contrast, the HVR was attenuated by LKB1 and AMPK deletion. However, in LKB1 knockouts hypoxia evoked hypoventilation, apnoea and Cheyne-Stokes-like breathing, while only hypoventilation and apnoea were observed after AMPK deletion. We therefore identify LKB1 as an essential regulator of carotid body chemosensing and uncover a divergence in dependency on LKB1 and AMPK between the carotid body on one hand and the HVR on the other.

The hypoxic ventilatory response (HVR) is critical to breathing and thus oxygen supply to the body and is primarily mediated by the carotid bodies. Here we reveal that carotid body afferent discharge during hypoxia and hypercapnia is determined by the expression of Liver Kinase B1 (LKB1), the principal kinase that mediates AMPK activation during metabolic stresses. Conversely, conditional deletion in catecholaminergic cells of AMPK, the principal downstream target of LKB1, had no effect on carotid body responses to hypoxia or hypercapnia. By contrast, the HVR was attenuated by LKB1 and AMPK deletion. However, in LKB1 knockouts hypoxia evoked hypoventilation, apnoea and Cheyne Stokes like breathing, while only hypoventilation and apnoea were observed after AMPK deletion. We therefore identify LKB1 as a novel and essential regulator of carotid body chemo-sensing and uncover a divergence in dependency on LKB1 and AMPK between the carotid body on one hand and the HVR on the other.