Biology subjects

Savva, C.

Publications and source records attributed to Savva, C..

8 recordsLinked to original sources

bioRxiv2026

A systemic circadian nicotinic acid riboside (NaR) signal engages the unfolded protein response and adipogenesis via the prefoldin complex

Daily light-dark cycles impose predictable environmental fluctuations that require coordinated temporal regulation of cellular physiology. This coordination is mediated by the circadian clock, which operates as a network of tissue oscillators; however, the molecular signals that convey circadian information between organs remain incompletely defined. Here, we identify nicotinic acid riboside (NaR) as a circulating metabolite whose rhythmicity depends on the liver clock. In differentiating 3T3-L1 adipocytes, NaR engages unfolded protein response (UPR) gene programs and modulates adipogenic competence. Proteome-wide stability profiling implicates the prefoldin complex as a molecular target of NaR signaling, linking NaR exposure to altered proteostasis. Functionally, NaR-induced UPR signaling converges on the adipogenic transcription factor CEBPA, which is a central regulator of adipogenesis. Importantly, sustained NaR exposure suppresses adipocyte lipid deposition, whereas temporally restricted NaR stimulation enhances adipogenesis, indicating that NaR acts in a time-dependent manner. Together, these findings identify NaR as a liver clock-controlled circulating metabolite that couples systemic circadian metabolism to adipocyte proteostasis and differentiation, revealing a mechanism by which temporal metabolic signals shape tissue-specific physiological outcomes. HighlightsO_LIThe circadian clock is required for rhythmic regulation of circulating nicotinic acid riboside (NaR). C_LIO_LIThe liver clock is sufficient to generate NaR rhythmicity. C_LIO_LINaR engages the prefoldin complex to regulate unfolded protein response signaling and Cebpa expression. C_LIO_LITime-dependent NaR exposure differentially regulates CEBPA levels and adipocyte lipid deposition. C_LI

systems biology↗

bioRxiv2025

CenSegNet: a generalist high-throughput deep learning framework for centrosome phenotyping at spatial and single-cell resolution in heterogeneous tissues

Centrosome abnormalities (CA) are a hallmark of epithelial cancers, yet their spatial complexity and phenotypic heterogeneity remain poorly resolved due to limitations in conventional image analysis. We present CenSegNet (Centrosome Segmentation Network), a modular deep learning framework for high-resolution, context-aware segmentation of centrosomes and epithelial architecture across diverse tissue types. Integrating a dual-branch architecture with uncertainty-guided refinement, CenSegNet achieves state-of-the-art performance and generalisability across both immunofluorescence and immunohistochemistry modalities, outperforming existing models in accuracy and morphological fidelity. Applied to tissue microarrays (TMAs) containing 911 breast cancer sample cores from 127 patients, CenSegNet enables the first large-scale, spatially resolved quantification of numerical and structural CA at single-cell resolution. These CA subtypes are mechanistically uncoupled, exhibiting distinct spatial distributions, age-dependent dynamics, and associations with histological tumour grade, hormone receptor status, genomic alterations, and nodal involvement. Structural CA levels are additionally associated with overall survival, supporting the clinical relevance of spatially resolved CA patterns. Discordant CA profiles at tumour margins are linked to local aggressiveness and stromal remodelling. To support broad adoption and reproducibility, CenSegNet is released as an open-source Python library. Together, our findings establish CenSegNet as a scalable, generalisable platform for spatially resolved centrosome phenotyping in intact tissues, enabling systematic dissection of the biology of this organelle and its dysregulation in cancer and other epithelial diseases.

cell biology↗

bioRxiv2023

Estrogen receptor activation remodels TEAD1 gene expression to alleviate nonalcoholic fatty liver disease

IntroductionThe occurrence of obesity-related hepatic malignancies differs between sexes, suggesting the involvement of sex hormones. Female sex hormones maintain cell homeostasis through estrogen receptor (ER) signaling and protect from developing nonalcoholic fatty liver disease (NAFLD) in mice and humans. RationaleTo understand recovery from high-fat diet (HFD)-induced liver disease in males upon estrogen treatment, we comprehensively characterized molecular changes in the liver upon selective activation of estrogen receptors (ERs) to identify novel therapeutic targets downstream of estrogen signaling. MethodsTo dissect hepatic ER isoform-driven responses, we integrated liver transcriptomes from female and male HFD mice treated with or without four different estrogen agonists, along with multiomics data, including bulk, single-cell and spatial transcriptomics, chromatin profiling, machine learning models and advanced microscopy. Patient cohorts and primary human hepatocyte spheroids datasets were included. ResultsOnly males developed liver steatosis. We found that selective activation of either ER or ER{beta} reduced HFD-induced hepatic steatosis in male mice. Systemic ER activation restored HFD-induced aberrant gene expression of cellular processes across liver cell types, including hepatocytes. Profiling of marked histones revealed that ER activation modulated promoter and enhancer sites and identified 68 estrogen-sensitive enhancer-gene pairs. Most of these genes were similarly deregulated in human nonalcoholic fatty liver disease (NAFLD) patients, including the transcription factor TEAD1. TEAD1 expression increased in NAFLD patients, and inhibiting TEAD ameliorated steatosis in spheroids by suppressing lipogenic pathways. ConclusionsSystemic activation of ER or ER{beta} modulates molecular pathways in the liver to counteract NAFLD. Our study identified TEAD1 as a key ER-sensitive gene and suggested that its inhibition poses a therapeutic strategy to combat NAFLD without the undesired side effects elicited by estrogen signaling. Clinical research relevanceWe identified drug targets downstream of estrogen signaling, including TEAD1, and demonstrate that TEAD inhibition improves steatosis by suppressing lipogenic pathways. Basic research relevanceThe targeted activation of nuclear ERs recovers high-fat diet-induced molecular and physiological liver phenotypes by remodeling core pathways beyond lipid metabolism. ER-responsive enhancers regulate central metabolic genes of clinical significance in NAFLD patients, highlighting the potential impact of this research on understanding liver cell plasticity. HIGHLIGHTSO_LIsteatosis in livers of high-fat diet (HFD) male mice was effectively reduced by selective activation of estrogen receptors (ER and ER{beta}) with four different agonists. C_LIO_LIER agonist treatments successfully reversed HFD-induced changes in gene regulation and expression, revealing new treatment targets involving previously unconnected molecular pathways. C_LIO_LIestrogen-sensitive enhancers regulated important genes, including TEAD1, emerging as pivotal NAFLD regulators significantly impacting metabolic processes. C_LIO_LIhigh TEAD1 gene expression in NAFLD patients correlated with disease severity, underscoring its clinical significance in disease progression. C_LIO_LIinhibiting TEAD with small molecules alleviated steatosis by suppressing lipogenic pathways, resembling some of the same beneficial effects as estrogen treatment. C_LI

genomics↗

bioRxiv2021

Molecular programming in utero modulates hepatic lipid metabolism and adult metabolic risk in obese mother offspring in a sex-specific manner

Male and female offspring of obese mothers are known to differ significantly in their metabolic adaptation and later development of complications. We investigated the sex-dependent responses in obese offspring of mice with maternal obesity, focusing on changes in liver glucose and lipid metabolism. Maternal obesity prior to and during gestation led to hepatic insulin resistance and inflammation in male offspring, while female offspring were protected. These sex differences were explained by more efficient transcriptional and posttranscriptional reprogramming of metabolic pathways to prevent the damaging effects of maternal obesity in females compared to males. These differences were sustained later in life, resulting in a better metabolic balance in female offspring. In conclusion, sex and maternal obesity drive transcriptional and posttranscriptional regulation of major metabolic processes in offspring liver differently, explaining the sexual dimorphism in obesity-associated metabolic risk.

physiology↗

bioRxiv2021

Maternal obesity programs white and brown adipose tissue transcriptome and lipidome in offspring in a sex-dependent manner

The prevalence of overweight and obesity among children has drastically increased during the last decades and maternal obesity has been demonstrated as one of the ultimate factors. Nutrition-stimulated transgenerational epigenetic regulation of key metabolic genes is fundamental to the developmental origins of the metabolic syndrome. Fetal nutrition may differently influence female and male offspring. In this work, we investigated the sex-dependent programming of maternal obesity in visceral, subcutaneous and brown adipose tissues of offspring using magnetic resonance imaging and spectroscopy and a lipidomic approach combined with a Smart-Seq2 differential sequencing analysis. We show that the triglyceride profile varies between adipose depots, sexes and maternal diet. Our results demonstrate for the first time that a sex-dependent gene programming exists in visceral, subcutaneous and brown adipose tissues. Maternal obesity differentially programs gene expression in adipose depots of female and male offspring, which may contribute to the sex-dependent metabolic complications later in life. Graphical abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=146 SRC="FIGDIR/small/430188v1_ufig1.gif" ALT="Figure 1"> View larger version (34K): org.highwire.dtl.DTLVardef@8ceac8org.highwire.dtl.DTLVardef@18a2a32org.highwire.dtl.DTLVardef@1d8530dorg.highwire.dtl.DTLVardef@1349512_HPS_FORMAT_FIGEXP M_FIG C_FIG

cell biology↗

bioRxiv2020

Conformational changes and channel gating induced by CO2 binding to Connexin26

CO2 is the inevitable by-product of oxidative metabolism. Many physiological processes such as breathing1 and cerebral blood flow2 are sensitive to CO2. Historically, the physiological actions of CO2 have been regarded as being mediated exclusively via changes in pH. Here, we change this consensus by showing that the gap junction protein Connexin26 (Cx26) acts as a receptor for CO2 showing sensitivity to modest changes in PCO2 around the physiological norm3-6. Mass spectrometry analysis7 shows that CO2 carbamylates specific lysines on a regulatory loop of Cx26 at high, but not at low levels of PCO2. By means of high resolution cryo-EM, we have solved structures of Cx26 gap junctions at 1.9, 2.2 and 2.1 [A] for PCO2 of 90, 55 and 20 mmHg respectively, all at pH 7.4. Classification of the particles at each level of PCO2, shows the transmembrane helices and N-terminal helix flexing at the dynamic cytoplasmic side of the protein. Gating of Cx26 gap junctions by CO2 involves movements of the N-terminus to plug the channel at high PCO2. We therefore provide mechanistic detail for a new paradigm by which CO2 can directly control breathing8 and other key physiological functions9.

biochemistry↗

bioRxiv2020

High-fat diet impacts the colon and its transcriptome in a sex-dependent manner that is modifiable by estrogens

Epidemiological studies highlight a strong association between obesity and colorectal cancer (CRC), especially in men. Estrogen, on the other hand, is associated with protection against both the metabolic syndrome and CRC. The colon is the first organ to respond to a high-fat diet (HFD), and estrogen receptor beta (ER{beta}) in the intestine appears to prevent CRC. How estrogen impacts the colon under HFD condition has, however, not been investigated. Estrogen can act through three different receptors (ER, ER{beta}, GPER1) which all may impact metabolism. In an effort to dissect this, we fed mice a control diet or a high-fat diet (HFD) for 13 weeks and administered receptor-selective estrogenic ligands for the last three weeks. We recorded corresponding physiological impact on fat distribution, fasting glucose, colon crypt proliferation and immune cell infiltration, and the colon transcriptome response. We identify clear sex-differences at the transcriptome level, both at base line and after HFD and ligand treatments. An unexpected observation was the significant sex-differences and impact by HFD and estrogens on circadian clock gene expression, such as Npas2 and Arntl (Bmal1), in the colon. Both sexes also exhibited an increased infiltration of F4/80+ macrophages as a result of HFD. In males, but not females, this was accompanied by changes in colonic epithelial cell proliferation. ER-selective PPT treatment had significant systemic effects, reducing body weight in both sexes, whereas ER{beta}-selective DPN treatment did not impact body weight, but reduced infiltration of F4/80+ macrophages in colon of both sexes and attenuated HFD-induced proliferation of male colon crypts. Both ER and ER{beta} activation contributed to circadian clock gene regulations. We detail for the first time how HFD and estrogens modulate the colon transcriptome and physiology in a sex and ER-specific manner.

cell biology↗

bioRxiv2019

Structure of the processive human Pol δ holoenzyme

In eukaryotes, DNA polymerase {delta} (Pol {delta}) bound to the proliferating cell nuclear antigen (PCNA) replicates the lagging strand and cooperates with flap endonuclease 1 (FEN1) to process the Okazaki fragments for their ligation. We present the high-resolution cryo-EM structure of the human processive Pol {delta}-DNA-PCNA complex in the absence and presence of FEN1. Pol {delta} is anchored to one of the three PCNA monomers through the C-terminal domain of the catalytic subunit. The catalytic core sits on top of PCNA in an open configuration while the regulatory subunits project laterally. This arrangement allows PCNA to thread and stabilize the DNA exiting the catalytic cleft and recruit FEN1 to one unoccupied monomer in a toolbelt fashion. Alternative holoenzyme conformations reveal important functional interactions that maintain PCNA orientation during synthesis. This work sheds light on the structural basis of Pol {delta}s activity in replicating the human genome.

biochemistry↗