Biology subjects

Courjaret, R.

Publications and source records attributed to Courjaret, R..

4 recordsLinked to original sources

bioRxiv2026

A Quartet of Native Orai Channel Isoforms Orchestrates Graded NFAT Activation and Transcription

The Ca{superscript 2} release-activated Ca{superscript 2} (CRAC) channel mediates store-operated calcium entry (SOCE), a ubiquitous pathway essential for many cell types, including immune cells. Three Orai (Orai1/2/3) proteins constitute the plasma membrane pore-forming units of CRAC channels that are activated by the endoplasmic reticulum (ER) Ca2+-sensing STIM1/2 proteins when ER Ca2+ stores are depleted. Orai1/2/3 are differentially expressed across primary cells with discernible differences in their structures and biophysical properties. Further, Orai1 has two alternatively translated isoforms: long mammalian-specific Orai1 and the 63-residue shorter Orai1{beta}, which is evolutionarily older and conserved across vertebrates. Whether Orai1/1{beta}/2/3 produce unique cytosolic Ca{superscript 2} signatures that bias transcriptional responses through effectors like NFAT is unclear. Here, we used HEK293 cells engineered to express one native Orai isoform and show that all Orai isoforms couple to NFAT1/4 induction. The magnitude of NFAT1/4 induction for each Orai isoform matches that of SOCE, with the following profile: Orai1{beta}>Orai1>>Orai2>Orai3. Near-native re-expression of either Orai1 or Orai1{beta} in primary murine Orai1-/- CD4 T cells restored SOCE, NFAT activation, cytokine production and promoted near identical transcriptional responses enriched for immune activation pathways. An analysis of genetic and clinical data of human individuals showed that homozygous null mutations selectively abolishing Orai1 are not associated with disease resembling CRAC channelopathy. Primary T cells from individuals homozygous or heterozygous for an Orai1 null mutation showed enhanced, rather than impaired, SOCE and NFAT induction. Our data indicate that NFAT activation and transcriptional outputs are primarily driven by the graded strength of SOCE mediated by each isoform of the Orai quartet.

cell biology↗

bioRxiv2026

Membrane progesterone receptor signaling reverses hyperglycemia and insulin resistance in obese mice

Progesterone (P4) plays key roles in reproductive and metabolic function and signals through two receptor classes: classical nuclear receptors that regulate gene transcription and membrane progesterone receptors (mPR) that mediate rapid, non-genomic signaling. Whether mPR signaling influences systemic glucose homeostasis remains unclear. Here, we investigated whether mPR activation regulates glucose homeostasis and insulin sensitivity. Using the selective mPR agonist OD02-0, we show that mPR activation enhances glucose uptake in skeletal muscle and hepatocytes, associated with AMP-activated protein kinase (AMPK) activation. In HepG2 cells, mPR activation induces metabolic reprogramming characterized by reduced mitochondrial respiration and increased glycolytic flux. Pharmacological inhibition of AMPK suppresses this effect, indicating that these responses require AMPK activity. In diet-induced obese mice, chronic mPR activation reduces fasting glucose and insulin levels, improves glucose tolerance, and restores glucose-stimulated insulin secretion without detectable toxicity. Integrated proteomic and phosphoproteomic analyses in mouse liver reveal modulation of AMPK signaling and inhibition of mTORC1. Transcriptomic changes were limited, supporting a predominantly non-genomic mode of action. Together, these findings identify mPR signaling as a regulator of glucose homeostasis that engages central energy-sensing pathways to improve metabolic control in obesity.

physiology↗

bioRxiv2023

Architecture of Ca2+ tunneling, a basic Ca2+ signaling modality important for secretion

Ca2+ tunneling is a signaling modality that requires both Store-operated Ca2+ entry (SOCE) and Ca2+ release from the endoplasmic reticulum (ER). Tunneling expands the SOCE microdomain at ER-plasma membrane (PM) contact sites (ERPMCS) through Ca2+ uptake by the sarco/endoplasmic reticulum Ca2+ ATPase (SERCA) into the ER lumen where it diffuses and is released via open inositol trisphosphate (IP3) receptors (IP3Rs). In this study using high resolution imaging, we outline the spatial remodeling of the Ca2+ tunneling machinery (IP3R1; SERCA; PMCA; and Ano1 as an effector) relative to STIM1 in response to store depletion. We show that store depletion leads to redistribution of these Ca2+ signaling modulators to distinct subdomains laterally at the PM and axially within the cortical ER. To functionally define the role of Ca2+ tunneling, we engineered a Ca2+ tunneling attenuator (CaTAr) that blocks tunneling without affecting Ca2+ release or SOCE. CaTAr inhibits Cl- secretion in sweat gland cells. Viral mediated expression of CaTAr in the mouse reduces sweating, showing that Ca2+ tunneling is important physiologically. Collectively our findings outline the architecture of the Ca2+ tunneling machinery and show that it is a fundamental physiological pertinent Ca2+ signaling modality.

cell biology↗

bioRxiv2023

ER-Mitochondria Contact Sites expand during mitosis

Membrane contact sites between various organelles define specialized spatially defined signaling hubs, they are of great interest to better understand inter-organelle communication and its implications on cellular physiology. ER-mitochondria contact sites (ERMCS) are one of the best studied and mediate Ca2+ signaling that regulates mitochondrial bioenergetics. However, little is known about ERMCS during mitosis. Here we show that ERMCS expand during mitosis using transmission electron microscopy, serial EM coupled to 3D reconstruction, and ERMCS markers. ERMCS expansion in mitosis is functionally significant as it is associated with enhanced Ca2+ coupling between the ER and mitochondria resulting in heightened activation of mitochondrial dehydrogenases. Our data suggest that ERMCS remodeling in mitosis is important to meet the increased energy needs during cell division.

cell biology↗