Biology subjects

Kearney, M. T.

Publications and source records attributed to Kearney, M. T..

9 recordsLinked to original sources

bioRxiv2026

Sympathetic activation and the force-frequency relationship in heart failure with reduced ejection fraction

Background Limited heart rate rise contributes to reduced exercise tolerance for people who have heart failure with reduced ejection fraction (HFrEF), yet rate-adaptive pacing does not improve functional capacity due to an attenuated force-frequency relationship (FFR). How the FFR relates to total peripheral resistance and sympathetic tone in HFrEF is unknown. Methods In a prospective, observational study, participants with HFrEF and controls underwent an incremental pacing protocol, during which heart rate was increased from 50 to 140 beats per minute. At each heart rate increment LV contractility was measured by echocardiography to determine the FFR, as well as continuous beat-to-beat measurement of systolic and diastolic blood pressures with a plethysmography device to determine cardiac output, total peripheral resistance and blood pressure variability (BPV). A microneurography study was then conducted to measure muscle sympathetic nerve activity (MSNA) during incremental pacing. Results A total of 157 participants with HFrEF and 55 controls (mean age 71.1{+/-}1.4 years, 172 (81.1%) male) underwent the pacing protocol. We observed single units in seven of 11 participants who participated in the microneurography study. In both groups, LV contractility and cardiac output increased until the peak of the FFR, after which these declined. We observed a reduction in total peripheral resistance, blood pressure variability, MSNA frequency and incidence coinciding with the peak of the FFR, beyond which these increased. Whilst these relationships were present in both groups, they were more evident in participants with HFrEF. Conclusions For people with HFrEF there is a bidirectional relationship between heart rate and sympathetic activation, with a nadir of sympathetic tone occurring at the peak of the FFR. Both excessively low and high heart rates are accompanied by greater sympathetic activation. Taken together, these data suggest that optimal heart rate targets for HFrEF are likely to be individual.

physiology↗

bioRxiv2025

Tissue-specific endothelial cell heterogeneity in human type 2 diabetes

Transcriptomic heterogeneity of microvascular endothelial cells (MVEC) within subcutaneous adipose tissue (SAT) in preclinical models of obesity/type 2 diabetes mellitus (T2DM) is well-established. Here, we examined if such heterogeneity exists between two canonical insulin-target tissues, SAT and skeletal muscle (SkM). Characterisation of SAT and SkM MVEC from humans with T2DM demonstrated that SAT, but not SkM, exhibited cellular stress at transcriptomic, morphological, and protein levels.

cell biology↗

bioRxiv2025

Murine limb ischaemia induces structural and functional remodelling of local and distant bone marrow

Peripheral arterial disease (PAD) can induce bone marrow (BM) ischaemia, although little is known about the implications of this for local and systemic haematopoiesis. We explored the impact of murine unilateral hind-limb ischaemia (HLI) surgery on the structure and function of the ischaemic and non-ischaemic BM, versus control mice without HLI surgery. Abnormal BM hypoxia was present in the ischaemic limb 7-days post-HLI, with normalisation by 28-days. Histological analysis revealed the ischaemic BM to undergo profound vascular remodelling at 7-days that normalised by 61-days, along with a progressive accumulation of BM lipid droplets between 7- and 61-days; no structural changes were observed in the non-ischaemic limb BM. Flow cytometry revealed increased abundance of monocytes and inflammatory monocytes in the non-ischaemic and ischaemic BM 7-days post-HLI, with this persisting at 61-days in the non-ischaemic limb. In both limbs, we observed a progressive decline in the abundance of lineage-Sca-1+c-Kit+ haematopoietic stem cells. RNA-sequencing of BM-derived macrophages (BMDMs) revealed substantial transcriptomic differences between unstimulated control, ischaemic limb and non-ischaemic limb BMDMs. Moreover, there were also substantial transcriptomic differences between lipopolysaccharide-stimulated control and ischaemic limb BMDMs. However, we observed minimal differences in chromatin accessibility of unstimulated BMDMs from the 3 groups. Collectively, our data show that BM ischaemia has transient and sustained structural implications, along with both local and systemic effects on haematopoiesis and myeloid cell function. These findings suggest that PAD may have important consequences for systemic immune responses.

immunology↗

bioRxiv2024

Small molecule modulation of insulin receptor-insulin like growth factor-1 receptor heterodimers in human endothelial cells

ObjectivesThe insulin receptor (IR) and insulin like growth factor-1 receptor (IGF-1R) are heterodimers consisting of two extracellular -subunits and two transmembrane {beta} -subunits. Insulin {beta} and insulin like growth factor-1 {beta} hemi-receptors can heterodimerize to form hybrids composed of one IR {beta} and one IGF-1R {beta}. The function of hybrids in the endothelium is unclear. We sought insight by developing a small molecule capable of reducing hybrid formation in endothelial cells. MethodsWe performed a high-throughput small molecule screening, based on a homology model of hybrid structure. Endothelial cells were studied using western blotting and qPCR to determine the effects of small molecules that reduced hybrid formation. ResultsOur studies unveil a first-in-class quinoline-containing heterocyclic small molecule that reduces hybrids by >50% in human umbilical vein endothelial cells (HUVECs) with no effects on insulin or insulin like growth factor-1 receptors. This small molecule reduced expression of the negative regulatory p85 subunit of phosphatidylinositol 3-kinase, increased basal phosphorylation of the downstream target Akt and enhanced insulin/insulin-like growth factor-1 and shear stress-induced serine phosphorylation of Akt. In primary saphenous vein endothelial cells (SVEC) from patients with type 2 diabetes mellitus undergoing coronary artery bypass (CABG) surgery, hybrid receptor expression was greater than in patients without type 2 diabetes mellitus. The small molecule significantly reduced hybrid expression in SVEC from patients with type 2 diabetes mellitus. ConclusionsWe identified a small molecule that decreases the formation of IR: IGF-1R hybrid receptors in human endothelial cells, without significant impact on the overall expression of IR or IGF-1R. In HUVECs, reduction of IR: IGF-1R hybrid receptors leads to an increase in insulin-induced serine phosphorylation of the critical downstream signalling kinase, Akt. The underpinning mechanism appears, at least in part to involve the attenuation of the adverse effect of IR: IGF-1R hybrid receptors on PI3-kinase signalling. HighlightsO_LIWe have discovered a small molecule (HI) that inhibits insulin receptor/IGF-1 receptor hybrid formation. C_LIO_LIHI reveals previously unrecognised actions of insulin receptor/IGF-1 receptor hybrids distinct to insulin and IGF-1 receptors in endothelial cells. C_LIO_LITreatment of endothelial cells with HI enhances activity of the downstream signalling kinase Akt due to inhibitory regulation via PI3-K. C_LI

cell biology↗

bioRxiv2024

Using site-directed mutagenesis to further the understanding of insulin receptor-insulin like growth factor-1 receptor heterodimer structure.

Type 2 diabetes is characterised by the disruption of insulin and insulin-like growth factor (IGF) signalling. The key hubs of these signalling cascades - the Insulin receptor (IR) and Insulin-like growth factor 1 receptor (IGF1R) - are known to form functional IR-IGF1R hybrid receptors which are insulin resistant. However, the mechanisms underpinning IR-IGF1R hybrid formation are not fully understood, hindering the ability to modulate this for future therapies targeting this receptor. To pinpoint suitable sites for intervention, computational hotspot prediction was utilised to identify promising epitopes for targeting with point mutagenesis. Specific IGF1R point mutations F450A, R391A and D555A show reduced affinity of the hybrid receptor in a BRET based donor-saturation assay, confirming hybrid formation could be modulated at this interface. These data provide the basis for rational design of more effective hybrid receptor modulators, supporting the prospect of identifying a small molecule that specifically interacts with this target.

molecular biology↗

bioRxiv2021

A small molecule reveals role of insulin receptor-insulin like growth factor-1 receptor heterodimers

The insulin receptor and insulin like growth factor-1 receptor are heterodimers consisting of two extracellular -subunits and two transmembrane {beta}-subunits. IR {beta} and IGF1R {beta} hemi-receptors can heterodimerize to form hybrids composed of one IR {beta} and one IGF1R {beta}. Widely distributed in mammalian tissues, in contrast to IR and IGF1R the physiological function of hybrids is unclear. To identify tool compounds that inhibit hybrid formation we performed a high-throughput small molecule screen based on a homology model of hybrid structure. Our studies unveil a first in class quinoline-containing heterocyclic small molecule that reduces hybrids by >50% in human umbilical vein endothelial cells with no effect on IR or IGF1R expression. Downstream of IR and IGF1R our small molecule led to reduced expression of the negative regulatory p85 subunit of phosphatidylinositol 3-kinase, an increase in phosphorylation of its downstream target Akt and enhanced insulin and shear-induced phosphorylation of Akt. We show that hybrids have a role in human endothelial cell physiology distinct from IR and IGF1R.

cell biology↗

bioRxiv2019

Reduced insulin and IGF-1 signalling synergistically extend healthspan in male mice

Reduced IGF-1 signalling is an evolutionarily conserved mediator of longevity, yet the magnitude of this effect is substantially larger in organisms retaining a common insulin and IGF-1 receptor. Whether this discrepancy reflects the failure to simultaneously reduce IGF-1 and insulin signalling in mammalian model systems remains unexplored. Moreover, studies of invertebrates cannot ascertain whether substantial effects upon lifespan are associated with preserved cognitive performance, a crucial component of healthspan. We compared the healthspan of male mice with haploinsufficiency of the insulin receptor (IRKO), IGF-1 receptor (IGF-1RKO), or both (DKO), with wildtype (WT) littermates. DKO mice survived longer than WT, with IRKO and IGF-1RKO being intermediate. At 2 years of age, DKO also exhibited preserved nesting behaviour in contrast with all other genotypes. Differential insulin sensitivity or weight gain during ageing did not explain the preserved healthspan of DKO, since these were comparable to IRKO littermates. These data provide the first demonstration that reduced insulin and IGF-1 signalling have synergistic effects upon healthspan in a mammalian model system, suggesting future mechanistic and translational studies should target insulin and IGF-1 signalling.

cell biology↗

bioRxiv2018

Aged insulin resistant macrophages reveal dysregulated cholesterol biosynthesis, a pro-inflammatory profile and reduced foam cell formation capacity

Insulin resistance is the central defining feature of type 2 diabetes and an independent risk factor for the development of atherosclerosis. In addition, aging is a major risk factor in the development of insulin resistance and cardiovascular disease. Macrophages play a pivotal roles the the developments of diabetes and atherosclerosis and express insulin receptors. Despite their relevance however, the effect of insulin and insulin resistance on macrophages regarding their inflammatory status, foam cell formation capacity and affect on atherosclerosis are unclear. By taking advantage of a mouse model that recapitulates the effects of chronic PI3K pathway hyperstimulation in macrophages through SHIP2 knock-down, we show that insulin resistance in aged macrophages promotes a proinflammatory phenotype while modulating the cholesterol biosynthesis pathway. These altered characteristics may contribute to the development of chronic inflammatory disease frequently observed with age. Moreover, aged insulin-resistant proinflammatory macrophages display an altered response to acute inflammatory stimulus and reduced foam cell formation capacity. Our work also highlights for the first time, the complex and contrasting immunomodulatory effects of insulin on macrophages in aged mice.\n\nSignificanceO_LIFirst study to explore the effects of macrophage insulin resistance in aged cells.\nC_LIO_LIInsulin resistance in aged macrophages results in the reprogramming of the transcriptome with more than 4000 genes being differentially regulated.\nC_LIO_LIInsulin resistance in aged macrophages results in upregulation of IFN signalling pathway, cholesterol biosynthesis pathway and inflammasome gene expression.\nC_LIO_LIInsulin directly regulates macrophage cholesterol biosynthesis, IFN and inflammasome gene expression in a time- and dose-dependent manner.\nC_LIO_LIInsulin resistant aged macrophages exhibit reduced capacity to become foam cells.\nC_LI

immunology↗

bioRxiv2018

Piezo1 channel agonist mimics high glucose as a stimulator of insulin release

ObjectiveGlucose and hypotonicity induced cell swelling stimulate insulin release from pancreatic {beta}-cells but the mechanisms are poorly understood. Recently, Piezo1 was identified as a mechanically-activated nonselective Ca2+ permeable cationic channel in a range of mammalian cells. As cell swelling induced insulin release could be through stimulation of Ca2+ permeable stretch activated channels, we hypothesised a role for Piezo1 in cell swelling induced insulin release.\n\nMethodsTwo rat {beta}-cell lines (INS-1 and BRIN-BD11) and freshly-isolated mouse pancreatic islets were studied. Intracellular Ca2+ measurements were performed using the fura-2 Ca2+ indicator dye. Piezo1 agonist Yoda1, a competitive antagonist of Yoda1 (Dooku1) and an inactive analogue of Yoda1 (2e) were used as chemical probes. Piezo1 mRNA and insulin secretion were measured by RT-PCR and ELISA respectively.\n\nResultsPiezo1 mRNA was detected in both {beta}-cell lines and mouse islets. Yoda1 evoked Ca2+ entry which was inhibited by Yoda1 antagonist Dooku1 as well as other Piezo1 inhibitors gadolinium and ruthenium red, and not mimicked by 2e. Yoda1, but not 2e, stimulated Dooku1-sensitive insulin release from {beta}-cells and pancreatic islets. Hypotonicity and high glucose increased intracellular Ca2+ and enhanced Yoda1 Ca2+ influx responses. Pre-treatment with ruthenium red significantly reduced hypotonicity induced insulin release from {beta}-cells and pancreatic islets.\n\nConclusionThe data show that Piezo1 channel agonist induces insulin release from {beta}-cell lines and mouse pancreatic islets suggesting a role for Piezo1 in cell swelling induced insulin release. Hence Piezo1 agonists have a potential to be used as enhancers of insulin release.

cell biology↗