Biology subjects

Rolland, L.

Publications and source records attributed to Rolland, L..

9 recordsLinked to original sources

bioRxiv2026

Fatty acids from adipocyte lipolysis stimulate insulin secretion

White adipose tissue and pancreatic islets play central roles in the regulation of metabolic homeostasis. Although ectopic lipid accumulation is established as a driver of impaired insulin secretion, the acute contribution of adipocyte lipolysis to islet function remains poorly documented. Here, we investigated a mouse model with inducible adipocyte-specific deletion of both adipose triglyceride lipase (ATGL) and hormone-sensitive lipase (HSL), which leads to defective adipocyte lipolysis. Despite preserved ex vivo islet function, these mice displayed a marked reduction in insulin secretion in response to stimulation of adipocyte {beta}3-adrenoceptors, as well as following glucose and arginine challenges. Mechanistically, we identified non-esterified fatty acids as critical mediators of lipolysis-driven insulin secretion, engaging pancreatic signaling of the free fatty acid receptors FFAR4 (a.k.a. GPR120) and FFAR1 (a.k.a. GPR40). The regulation of insulin secretion by adipocyte lipolysis was preserved in high-fat diet-induced obesity. These findings identify an underappreciated adipose-islet crosstalk that couples adipocyte lipolysis to insulin secretion and links lipid and glucose metabolism.

physiology↗

bioRxiv2026

Loss of p27Kip1 causes metabolic reprogramming and is sufficient to induce a Warburg effect and glutamine addiction in untransformed cells

The metabolic needs of a cell are tightly linked to its proliferative state and increasing evidence indicate an extensive bidirectional crosstalk between metabolic pathways and cell cycle regulators. In cancer cells, metabolism is reprogrammed to couple energetic needs and relentless proliferation. The cyclin/CDK inhibitor p27Kip1 (p27) is frequently inactivated in cancers. p27 is also involved in multiple cellular processes, including transcriptional regulation or autophagy induction. Herein, we investigated the effect of p27 loss on cell metabolism. The knockout of p27 in immortalized mouse fibroblasts increases glucose uptake and glycolysis, while decreasing mitochondrial ATP production, consistent with induction of a Warburg effect, and this was accompanied by an increased glutamine dependency to feed the TCA cycle. Our data suggest that p27 loss causes this phenotype through extensive transcriptional remodeling of metabolic gene expression. Importantly, p27 silencing in human retinal RPE1-hTERT cells was sufficient to induce a Warburg effect. Together, these results reveal a new function of p27 in regulating energy metabolism and that loss of p27 expression is sufficient to induce metabolic reprogramming and a Warburg effect, suggesting that p27 inactivation in cancer cells not only results in the loss of cell cycle inhibition but also enables the metabolic rewiring needed for increased proliferation.

cell biology↗

bioRxiv2023

The ion channel Trpc6a regulates the cardiomyocyte regenerative response to mechanical stretch.

Myocardial damage caused for example by cardiac ischemia leads to ventricular volume overload resulting in increased stretch of the remaining myocardium. In adult mammals, these changes trigger an adaptive cardiomyocyte hypertrophic response which, if the damage is extensive, will ultimately lead to pathological hypertrophy and heart failure. Conversely, in response to extensive myocardial damage, cardiomyocytes in the adult zebrafish heart and neonatal mice proliferate and completely regenerate the damaged myocardium. We therefore hypothesized that in adult zebrafish, changes in mechanical loading due to myocardial damage may act as a trigger to induce cardiac regeneration. Based, on this notion we sought to identify mechanosensors which could be involved in detecting changes in mechanical loading and triggering regeneration. Here we show using a combination of knockout animals, RNAseq and in vitro assays that the mechanosensitive ion channel Trpc6a is required by cardiomyocytes for successful cardiac regeneration in adult zebrafish. Furthermore, using a cyclic cell stretch assay, we have determined that Trpc6a induces the expression of components of the AP1 transcription complex in response to mechanical stretch. Our data highlights how changes in mechanical forces due to myocardial damage can be detected by mechanosensors which in turn can trigger cardiac regeneration.

cell biology↗

bioRxiv2023

High-throughput quantitative screening of glucose-stimulated insulin secretion and insulin content using automated MAL-DI-TOF mass spectrometry

Type 2 diabetes (T2D) is a metabolic disorder characterized by loss of pancreatic {beta}- cell function, decreased insulin secretion and increased insulin resistance, that affects more than 400 million people worldwide. Although several treatments are proposed to patients suffering from T2D, long-term control of glycemia remains a challenge. Therefore, identifying new potential drugs and targets that positively affect {beta}-cell function and insulin secretion remains crucial. Here, we developed an automated approach to allow the identification of new compounds or genes potentially involved in {beta}-cell function in a 384-well plate format, using the murine {beta}-cell model Min6. Using MALDI-TOF mass spectrometry, we have implemented a high-throughput screening (HTS) strategy based on the automation of a cellular assay allowing to detect insulin secretion in response to glucose, quantitative detection of insulin, in a miniaturized system. As a proof of concept, we screened siRNA targeting well-know {beta}-cell genes and 1600 chemical compounds and identified several molecules as potential regulators of insulin secretion and/or synthesis, demonstrating that our approach allows HTS of insulin secretion in vitro.

physiology↗

bioRxiv2022

The HDAC inhibitor trichostatin A impairs pancreatic β-cell function through an epigenome-wide reprogramming

ObjectiveThe pancreatic islets of Langerhans contain distinct cell subtypes including insulin-producing {beta} cells. Although their cell-specific gene expression pattern defines their identity, the underlying molecular network driving this transcriptional specificity is not fully understood. Among the numerous transcriptional regulators, histone deacetylases (HDAC) enzymes are potent chromatin modifiers which directly regulate gene expression through deacetylation of lysine residues within specific histone proteins. The precise molecular mechanisms underlying HDAC effects on cellular plasticity and {beta}-cell identity are currently unknown. MethodsThe pharmacological inhibition of HDAC activity by trichostatin A (TSA) was studied in the mouse Min6 and human EndocBH1 cell lines, as well as primary mouse sorted {beta} cells and human pancreatic islets. The molecular and functional effects of treating these complementary {beta}-cell models with TSA was explored at the epigenomic and transcriptomic level through next-generation sequencing of chromatin immunoprecipitation (ChIP) assays (ChIP-seq) and RNA sequencing (RNA-seq) experiments, respectively. ResultsWe showed that TSA alters insulin secretion associated with {beta}-cell specific transcriptome programming in both mouse and human {beta}-cell lines, as well as on human pancreatic islets. We also demonstrated that this alternative {beta}-cell transcriptional program in response to HDAC inhibition is related to an epigenome-wide remodeling at both promoters and enhancers. ConclusionsTaken together, our data indicate that full HDAC activity is required to safeguard the epigenome, to protect against loss of {beta}-cell identity with unsuitable expression of genes associated with alternative cell fates.

genomics↗

bioRxiv2022

Characterization of the adult zebrafish electrocardiogram

BackgroundThe use of zebrafish to explore cardiac physiology has been widely adopted within the scientific community. Whether this animal model can be used to determine drug cardiac toxicity via electrocardiogram (ECG) analysis, is still an ongoing question. Several reports indicate that the recording configuration severely affects the ECG waveforms and its derived-parameters, emphasizing the need for improved characterization. MethodsECGs were recorded from adult zebrafish hearts in 3 different configurations (unexposed heart, exposed heart and extracted heart) to identify the most reliable method to explore ECG recordings at baseline and in response to commonly used clinical therapies. ResultsWe found that the exposed heart configuration provided the most reliable and reproducible ECG recordings of waveforms and intervals. We were unable to determine T-wave morphology in unexposed hearts. In extracted hearts, ECG intervals were lengthened and P-waves were unstable. However, in the exposed heart configuration, we were able to reliably record ECGs and subsequently establish the QT-RR relationship (Holzgrefe correction) in response to changes in heart rate. ConclusionsThe exposed heart configuration appears to be the most reliable technique to record ECGs in adult zebrafish. In this configuration, the QT-RR relationship, an important parameter in cardiac toxicity evaluation, can be determined using the Holzgrefe correction.

physiology↗

bioRxiv2021

The regenerative response of cardiac interstitial cells

Understanding how certain animals are capable of regenerating their hearts will provide much needed insights into how this process can be induced in humans in order to reverse the damage caused by myocardial infarction. Currently, it is becoming increasingly evident that cardiac interstitial cells play crucial roles during cardiac regeneration. To understand how interstitial cells behave during cardiac regeneration, we performed single-cell RNA sequencing (scRNA-seq) of regenerating zebrafish hearts. Using a combination of immunohistochemistry, chemical inhibition and novel transgenic animals, we were able to investigate the role of cell type specific responses during cardiac regeneration. This approach allowed us to identify a number of important regenerative mechanisms within the interstitial cell populations. Here, we provide here a detailed insight into how interstitial cells behave during cardiac regeneration and identify a number of novel features of these cells which will serve to increase our understanding of how this process could eventually be induced in humans.

cell biology↗

bioRxiv2021

A crosstalk between E2F1 and GLP-1 signaling pathways modulates insulin secretion

Compromised {beta}-cell function contributes to type 2 diabetes (T2D) development. The glucagon like peptide 1 (Glp-1) has emerged as a hormone with broad pharmacological potential toward T2D treatment, notably by improving {beta}-cell functions. Recent data have shown that the transcription factor E2f1, besides its role as a cell cycle regulator, is involved in glucose homeostasis by modulating {beta}-cell mass, function and identity. Here, we demonstrate a crosstalk between the E2F1, phosphorylation of retinoblastoma protein (pRb) and Glp-1 signaling pathways. We found that {beta}-cell specific E2f1 deficient mice (E2f1{beta}-/-) presented with impaired glucose homeostasis and decreased glucose stimulated-insulin secretion mediated by exendin 4 (i.e., GLP1R agonist), which were associated with decreased expression of Glp1r encoding Glp-1 receptor (GLP1R) in E2f1{beta}-/- pancreatic islets. Decreasing E2F1 transcriptional activity with an E2F inhibitor in islets from nondiabetic humans decreased GLP1R levels and blunted the incretin effect of exendin 4 on insulin secretion. Conversely, overexpressing E2f1 in pancreatic {beta} cells increased Glp1r expression associated with enhanced insulin secretion mediated by GLP1R agonist. Interestingly, kinome analysis of mouse islets demonstrated that an acute treatment with exendin 4 increased pRb phosphorylation and subsequent E2f1 transcriptional activity. This study suggests a molecular crosstalk between the E2F1/pRb and GLP1R signaling pathways that modulates insulin secretion and glucose homeostasis.

physiology↗

bioRxiv2020

Pancreatic β-cell specific loss of E2f1 impairs insulin secretion and β-cell identity through the epigenetic repression of non β-cell programs

The loss of pancreatic {beta}-cell identity emerges as an important feature of type 2 diabetes development, but the molecular mechanisms are still elusive. Here, we explore the cell-autonomous role of the cell cycle regulator and transcription factor E2F1 in the maintenance of {beta}-cell identity and insulin secretion. We show that the {beta}-cell-specific loss of E2f1 function in mice triggers glucose intolerance associated with defective insulin secretion, an altered -to-{beta}-cell ratio, a downregulation of many {beta}-cell genes and a concomitant increase of non-{beta}-cell markers. Mechanistically, the epigenomic profiling of non-beta cell upregulated gene promoters identified an enrichment of bivalent H3K4me3/H3K27me3 or H3K27me3 marks. Conversely, downregulated genes were enriched in active chromatin H3K4me3 and H3K27ac histone marks. We find that histone deacetylase inhibitors modulate E2F1 transcriptional and epigenomic signatures associated with these {beta}-cell dysfunctions. Finally, the pharmacological inhibition of E2F transcriptional activity in human islets also impairs insulin secretion and the expression of {beta}-cell identity genes. Our data suggest that E2F1 is critical for maintaining {beta}-cell identity through a sustained repression of non {beta}-cell transcriptional programs.

physiology↗