Biology subjects

Herzig, S.

Publications and source records attributed to Herzig, S..

At least 19 recordsLinked to original sources

bioRxiv2025

Endothelial deletion of ADGRF5 (GPR116) promotes fibro-inflammatory EndMT and impairs adaptive thermogenesis in brown adipose tissue

ObjectiveBrown adipose tissue (BAT) dissipates energy via non-shivering thermogenesis, and it is a promising therapeutic target for metabolic disease. While most research focuses on thermogenic adipocytes, emerging data point to critical contributions from the surrounding stromal niche. Here, we investigated the role of adhesion G protein-coupled receptors (aGPCRs) in BAT function, focusing on Adgrf5 (Gpr116), a receptor enriched in endothelial cells. MethodsWe used single-nuclei RNA sequencing to map aGPCRs expression across mouse and human BAT. We then examined the consequences of Adgrf5(Gpr116) loss using global, brown adipocyte, and endothelial-specific knockout mouse models under acute and prolonged cold exposure. ResultsInducible endothelial deletion of Adgrf5(Gpr116) impaired the maintenance of thermogenic capacity during prolonged--but not acute--cold exposure. This was not associated with defective angiogenesis, but rather with endothelial fibro-inflammatory reprogramming. Single-nuclei RNA sequencing analysis revealed endothelial-to- mesenchymal transition (EndMT) features, including induction of mesenchymal markers, collagens, and metalloproteinases, and loss of barrier genes. Adgrf5(Gpr116)-deficient endothelial cells also exhibited cytoskeletal remodeling and activation of stress fiber pathways, implicating Adgrf5(Gpr116) as a mechanosensory safeguard of endothelial identity. ConclusionEndothelial Adgrf5(Gpr116) preserves thermogenic competence in BAT by suppressing EndMT and maladaptive matrix remodeling. Our findings establish vascular mechanosensing as a critical determinant of thermogenic tissue homeostasis. HighlightsO_LIAdhesion GPCRs are the second most abundant GPCR family in mouse and human brown fat C_LIO_LIAdhesion GPCRs are enriched in non-adipocyte cell types in brown fat and participate in cell-cell contact signaling C_LIO_LIEndothelial Adgrf5(Gpr116) is required for thermogenic adaptation during prolonged cold exposure C_LIO_LILoss of Adgrf5(Gpr116) induces fibro-inflammatory reprogramming and endothelial-to-mesenchymal transition (EndMT) C_LI

molecular biology↗

bioRxiv2025

A genetic signature predicts aggressive paraganglioma sensitivity to dual PI3K-CDK4/6 inhibition therapy

Effective medical therapies for metastatic paraganglioma (mPPGL) are currently lacking, leading to dismal prognosis. Building on our knowledge of molecular mechanisms driving PPGL progression, we assessed the therapeutic potential of targeting two critical processes: PI3K signaling and cell cycle regulation. The efficacy of buparlisib (PI3Ki) and ribociclib (CDK4/6i), individually and combined, was assessed in vitro using PPGL cell lines, rat- and patient-derived primary cells, and in vivo using PPGL cells-derived mouse xenografts. The combination therapy demonstrated superior antitumor activity compared to single agents, particularly in vivo. Mechanistically, the efficacy of the combination therapy was associated to the downregulation of FOXM1-controlled genes implicated in mitotic spindle assembly and chromosomal segregation, leading to mitotic catastrophe. Data mining and qRT-PCR showed this genetic signature to be upregulated in human mPPGLs. This suggests that aggressive PPGLs exhibit heightened vulnerability to dual PI3K and CDK4/6 inhibition, offering a promising therapeutic avenue for these challenging cancers.

cancer biology↗

bioRxiv2024

Deep Learning and 3D Imaging Reveal Whole-Body Alterations in Obesity

Many diseases, such as obesity, have systemic effects that impact multiple organ systems throughout the body. However, tools for comprehensive, high-resolution analysis of disease-associated changes at the whole-body scale have been lacking. Here, we developed a suite of deep learning-based image analysis algorithms (MouseMapper) and integrated it with tissue clearing and light-sheet microscopy to enable a comprehensive analysis of diseases impacting diverse systems across the mouse body. This approach enables the quantitative analysis of cellular and structural changes across the entire mouse body at unprecedented resolution and scale, including tracking nerves over several centimeters in whole animal bodies. To demonstrate its power, we applied MouseMapper to study nervous and immune systems in high-fat diet induced obesity. We uncovered widespread changes in both immune cell distribution and nerve structures, including alterations in the trigeminal nerve characterized by a reduced number of nerve endings in obese mice. These structural abnormalities were associated with functional deficits of whisker sensing and proteomic changes in the trigeminal ganglion, primarily affecting pathways related to axon growth and the complement system. Additionally, we found heterogeneity in obesity-induced whole-body inflammation across different tissues and organs. Our study demonstrates MouseMappers capability to discover and quantify pathological alterations at the whole-body level, offering a powerful approach for investigating the systemic impacts of various diseases. Graphical Abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=187 SRC="FIGDIR/small/608300v1_ufig1.gif" ALT="Figure 1"> View larger version (74K): org.highwire.dtl.DTLVardef@17d2601org.highwire.dtl.DTLVardef@14a2d3dorg.highwire.dtl.DTLVardef@e04114org.highwire.dtl.DTLVardef@d0b8b5_HPS_FORMAT_FIGEXP M_FIG C_FIG HighlightsO_LIWe developed MouseMapper: AI-driven pipeline for whole-body structural analysis in mice C_LIO_LIMouseMapper revealed obesity-induced changes in nerves and immune cells across multiple organs C_LIO_LIMouseMapper identified facial nerve alterations in obesity linked to impaired whisker sensitivity C_LIO_LIMouseMapper has the potential for holistic 3D analysis of systemic diseases C_LI Supplementary Videos can be seen at: http://discotechnologies.org/MouseMapper/

systems biology↗

bioRxiv2024

Control of cholesterol-induced adipocyte inflammation by the Nfe2l1-Atf3 pathway

While adipocytes are critical pillars of energy metabolism, their dysfunction is linked to adipose tissue (AT) inflammation, insulin resistance, and ectopic lipotoxicity in cardiometabolic diseases. However, the mechanisms causing adipocyte inflammation and insulin resistance remain unclear. Here, we show that excess cholesterol induces adipocyte dysfunction, which is suppressed by the transcription factor Nfe2l1 (nuclear factor erythroid derived-2, like-1). Nfe2l1 is required to sustain proteasome function in adipocytes and proteotoxic stress induces adipocyte inflammation via the activation of Atf3. In humans, the Nfe2l1-proteasome pathway is inversely correlated to body mass index (BMI) in an adipose-depot specific manner. In mice, loss of adipocyte Nfe2l1 caused AT inflammation with a pronounced infiltration of macrophages and T cells. Mice lacking adipocyte Nfe2l1 displayed severe adipocyte dysfunction during diet-induced obesity (DIO), characterized by lower adipokine levels, steatosis, glucose intolerance and insulin resistance. Nfe2l1{Delta}AT mice on an Apoe-deficient (Apoe-/-) background fed a cholesterol-rich Western Diet (WD), developed a lipoatrophy-like syndrome, dyslipidemia, and enhanced atherosclerosis. Our results reveal an important role for proteasome-mediated proteostasis in adipocytes and indicate that Nfe2l1 is linked to metabolic health in humans and preclinical mouse models. Promoting proteostasis in adipocytes may thus alleviate inflammation in obesity, potentially averting adverse cardiometabolic outcomes. Graphical abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=191 SRC="FIGDIR/small/604614v1_ufig1.gif" ALT="Figure 1"> View larger version (61K): org.highwire.dtl.DTLVardef@145e32borg.highwire.dtl.DTLVardef@1454df1org.highwire.dtl.DTLVardef@1002383org.highwire.dtl.DTLVardef@1b7319_HPS_FORMAT_FIGEXP M_FIG C_FIG

physiology↗

bioRxiv2024

Endothelial cannabinoid CB1 receptor deficiency reduces arterial inflammation and lipid uptake in response to atheroprone shear stress

BackgroundPeripherally restricted cannabinoid CB1 receptor antagonists without central side effects hold promise for treating metabolic disorders including diabetes and obesity. In atherosclerosis, the specific effects of peripheral CB1 signaling in vascular endothelial cells (ECs) remain incompletely understood. Methods and resultsEndothelial expression of the CB1 encoding gene CNR1 was detectable in human plaque single-cell RNA sequencing data. In situ hybridization of Cnr1 in murine aortas revealed a significantly increased endothelial expression within atheroprone compared to atheroresistant regions. In vitro, CNR1 was upregulated by oscillatory shear stress (OSS) in human aortic endothelial cells (HAoECs). Endothelial CB1 deficiency (Cnr1EC-KO) in female mice on atherogenic background resulted in pronounced endothelial phenotypic changes, with reduced vascular inflammation and permeability. This resulted in attenuated plaque development with reduced lipid content in female mice, while reduced white and brown adipose tissue mass and liver steatosis were observed in both males and females. Ex vivo imaging of carotid arteries via two-photon microscopy revealed less labeled low density lipoprotein (Dil-LDL) uptake in Cnr1EC-KO. This was accompanied by a significant reduction of aortic endothelial caveolin-1 (CAV1) expression, a key structural protein involved in lipid transcytosis, in female Cnr1EC-KO mice. In vitro, pharmacological blocking with CB1 antagonist AM281 reproduced the inhibition of CAV1 expression and Dil-LDL uptake in response to atheroprone OSS in HAoECs, which was dependent on cAMP-mediated PKA activation. Conversely, the CB1 agonist ACEA increased Dil-LDL uptake and CAV1 expression in HAoECs. Finally, treatment of atherosclerotic mice with the peripheral CB1 antagonist JD-5037 reduced plaque progression, CAV1 and endothelial adhesion molecule expression in female mice. ConclusionsThese results confirm an essential role of endothelial CB1 to the pathogenesis of atherosclerosis. Peripheral CB1 antagonists may hold promise as an effective therapeutic strategy for treating atherosclerosis and related metabolic disorders. NOVELTY AND SIGNIFICANCEWhat is known? O_LIEnhanced endocannabinoid-cannabinoid CB1 receptor signaling has been implicated in metabolic disorders, atherosclerosis, and hypertension, but the cell-specific role of endothelial CB1 in atherosclerosis is not well understood. C_LIO_LIGlobal CB1 antagonists improve metabolic function and inhibit atherosclerotic plaque development in mouse models, but have failed in the clinic due to centrally mediated psychiatric side effects. C_LI What is new? O_LIBased on human single-cell RNA sequencing data, CB1 is expressed in human plaque ECs. C_LIO_LIUsing transgenic mouse models and human primary aortic endothelial cells, we provide evidence for a key role of CB1 in endothelial shear stress response, inflammatory gene expression, and LDL uptake. C_LIO_LIThe underlying signaling pathway of CB1-induced endothelial LDL uptake involves a cAMP-PKA-dependent regulation of caveolin 1 (CAV1) expression, a structural protein of the shear stress sensitive signaling domains of the plasma membrane. C_LIO_LIBy limiting endothelial CAV1 and VCAM1 expression, peripherally restricted CB1 antagonists confer atheroprotection in mice. C_LI Our findings reveal that endothelial CB1 expression is induced by atheroprone shear stress responses and contributes to impaired vascular barrier function, inflammation, and lipid uptake, thereby promoting atherosclerotic lesion formation and progression. By elucidating the transcriptomic pathways regulated by endothelial CB1 and its broad influence on lipid uptake and metabolism in arteries, liver, and brown and white adipose tissue, our study provides insights into novel pathways and potential interventions for the treatment of atherosclerosis and metabolic disorders. The use of peripherally restricted CB1 antagonists that specifically target vascular inflammation and tissue lipid storage could be a complementary and safe therapeutic avenue to treat cardiovascular and metabolic disease comorbidities without altering CB1 signaling in the brain.

immunology↗

bioRxiv2024

Chronic intermittent fasting impairs β-cell maturation and function in adolescent mice

Intermittent fasting (IF) is a nutritional lifestyle intervention with broad metabolic benefits, but whether the impact of IF depends on the individuals age is unclear. Here, we investigated the effects of IF on systemic metabolism and pancreatic islet function in old, middle-aged, and young mice. Short-term IF improved glucose homeostasis across all age groups, without altering islet function and morphology. In contrast, while chronic IF was beneficial for adult mice, it resulted in impaired {beta}-cell function in the young. Using scRNAseq, we delineated that the {beta}-cell maturation and function score were reduced in young mice. In human islets, a similar pattern was observed in Type 1 (T1D), but not in Type 2 diabetes (T2D), suggesting that the impact of chronic IF in adolescence is linked to the development of {beta}-cell dysfunction. Our study suggests considering the duration of IF in younger people, as it may enhance rather than reduce diabetes outcomes. Graphical abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=164 SRC="FIGDIR/small/590140v1_ufig1.gif" ALT="Figure 1"> View larger version (42K): org.highwire.dtl.DTLVardef@1676dd1org.highwire.dtl.DTLVardef@15ac993org.highwire.dtl.DTLVardef@167f577org.highwire.dtl.DTLVardef@247e4e_HPS_FORMAT_FIGEXP M_FIG C_FIG O_LILong-term IF impairs {beta}-cell function in adolescent mice. C_LIO_LIIF-induced impaired {beta}-cell function is associated with impaired proliferative capacity and lower levels of mature cells. C_LIO_LIIF-induced impaired {beta}-cell function is associated with a transcriptional change highly conserved in type 1-, but not type 2 diabetes. C_LI

physiology↗

bioRxiv2023

Virtual reality empowered deep learning analysis of brain activity

Tissue clearing and fluorescent microscopy are powerful tools for unbiased organ-scale protein expression studies. Critical for interpreting expression patterns of large imaged volumes are reliable quantification methods. Here, we present DELiVR a deep learning pipeline that uses virtual reality (VR)-generated training data to train deep neural networks, and quantify c-Fos as marker for neuronal activity in cleared mouse brains and map its expression at cellular resolution. VR annotation significantly accelerated the speed of generating training data compared to conventional 2D slice based annotation. DELiVR detects cells with much higher precision than current threshold-based pipelines, and provides an extensive toolbox for data visualization, inspection and comparison. We applied DELiVR to profile cancer-related mouse brain activity, and discovered a novel activation pattern that distinguishes between weight-stable cancer and cancer-associated weight loss. Thus, DELiVR provides a robust mouse brain analysis pipeline at cellular scale that can be used to study brain activity patterns in health and disease. The DELiVR software, Fiji plugin and documentation can be found at https://www.DISCOtechnologies.org/DELiVR/. Graphical Abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=169 SRC="FIGDIR/small/540970v1_ufig1.gif" ALT="Figure 1"> View larger version (66K): org.highwire.dtl.DTLVardef@172d5bforg.highwire.dtl.DTLVardef@2f1d80org.highwire.dtl.DTLVardef@139e7a0org.highwire.dtl.DTLVardef@95dce1_HPS_FORMAT_FIGEXP M_FIG C_FIG HighlightsO_LIDELiVR detects labelled cells in cleared brains with deep learning C_LIO_LIDELiVR is trained by annotating ground-truth data in virtual reality (VR) C_LIO_LIDELiVR is launched via a FIJI plugin anywhere from PCs to clusters C_LIO_LIUsing DELiVR, we found new brain activity patterns in weight-stable vs. cachectic cancer C_LI Supplementary Videos can be seen at: https://www.DISCOtechnologies.org/DELiVR/

bioinformatics↗

bioRxiv2023

Nfe2l1-mediated proteasome function controls muscle energy metabolism in obesity

Muscle function is an important denominator of energy metabolism and metabolic health. Adapting the myocyte proteome to energetic challenges, in response to diet or fasting, is facilitated by programs of proteostasis, but the adaptive role of the ubiquitin-proteasome system (UPS) in muscle remains unclear. Here, we show that myocyte Nuclear factor erythroid derived 2,-like 1 (Nfe2l1, also known as Nrf1) is a key regulator of skeletal muscle proteostasis and function. In mice and humans, Nfe2l1 is highly expressed in skeletal myocytes, and its loss diminishes proteasomal activity and leads to hyperubiquitylation. Mice lacking myocyte Nfe2l1 display muscle fiber type switching and insulin resistance when fed a high-fed diet. Nfe2l1 protects myocytes from ferroptosis, which is enhanced in the presence of excess lipids. In conclusion, we define a new adaptive role for the Nfe2l1-ubiquitin proteasome system in the control of skeletal muscle function and energy metabolism.

physiology↗

bioRxiv2023

Loss of myeloid cannabinoid CB1 receptor confers atheroprotection by reducing macrophage proliferation and immunometabolic reprogramming

Although the cannabinoid CB1 receptor has been implicated in atherosclerosis, its cell-specific effects in this disease are not well understood. Here, we report that male mice with myeloid-specific Cnr1 deficiency on atherogenic background developed smaller lesions and necrotic cores than controls, while only minor genotype differences were observed in females. Male Cnr1 deficient mice showed reduced arterial monocyte recruitment and macrophage proliferation with less inflammatory phenotype. The sex-specific differences were reproducible in bone marrow derived macrophages and blunted by estradiol. Kinase activity profiling revealed a CB1-dependent regulation of p53 and cyclin-dependent kinases. Transcriptomic profiling further unveiled chromatin modifications, mRNA processing and mitochondrial respiration among the key processes affected by CB1 signaling, which was supported by metabolic flux assays. Chronic administration of the peripherally-restricted CB1 antagonist JD5037 inhibited plaque progression and macrophage proliferation, but only in male mice. Finally, CNR1 expression was detectable in human carotid endarterectomy plaques and inversely correlated with proliferation, oxidative metabolism and inflammatory markers, hinting to a possible implication of CB1-dependent regulation in human pathophysiology. In conclusion, impaired CB1 signaling in macrophages is atheroprotective by limiting their arterial recruitment, proliferation and inflammatory reprogramming. The importance of macrophage CB1 signaling seems to be more pronounced in male mice. O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=105 SRC="FIGDIR/small/535832v2_ufig1.gif" ALT="Figure 1"> View larger version (30K): org.highwire.dtl.DTLVardef@1d0b2f4org.highwire.dtl.DTLVardef@94f1b4org.highwire.dtl.DTLVardef@8868edorg.highwire.dtl.DTLVardef@1a0b151_HPS_FORMAT_FIGEXP M_FIG C_FIG Graphical summary (created with BioRender.com)

immunology↗

bioRxiv2022

Fasting-sensitive SUMO-switch on Prox1 controls hepatic cholesterol metabolism

The liver is the major metabolic hub, ensuring appropriate nutrient supply during fasting and feeding. In obesity, accumulation of excess nutrients hampers proper liver function and is linked to non-alcoholic fatty liver disease. Understanding the signaling mechanisms that enable hepatocytes to quickly adapt to dietary cues, might help to restore balance in liver diseases. Post-translational modification by attachment of the Small Ubiquitin-like Modifier (SUMO), allows for a dynamic regulation of numerous processes including transcriptional reprograming. Here, we demonstrate that the specific SUMOylation of transcription factor Prox1 represents a nutrient-sensitive determinant of hepatic fasting metabolism. Prox1 was highly modified by SUMOylation on lysine 556 in the liver of ad libitum and re-fed mice, while this modification was strongly abolished upon fasting. In a context of diet-induced obesity, Prox1 SUMOylation became insensitive to fasting cues. Hepatocyte-selective knock in of a SUMOylation-deficient Prox1 mutant into mice fed a high fat/high fructose diet led to reduction of systemic cholesterol levels, associated with the induction of bile acid detoxifying pathways in mutant livers during fasting. As appropriate and controlled fasting protocols have been shown to exert beneficial effects on human health, tools to maintain the nutrient-sensitive SUMOylation switch on Prox1 may thus contribute to the development of "fasting-based" approaches for the maintenance of metabolic health.

physiology↗

bioRxiv2021

Hepatocyte-specific activity of TSC22D4 triggers progressive NAFLD by impairing mitochondrial function

ObjectiveFibrotic organ responses have recently been identified as long-term complication in diabetes. Indeed, insulin resistance and aberrant hepatic lipid accumulation represent driving features of progressive non-alcoholic fatty liver disease (NAFLD), ranging from simple steatosis and non-alcoholic steatohepatitis (NASH) to fibrosis. Effective pharmacological regimens to stop progressive liver disease are still lacking to-date. MethodsBased on our previous discovery of transforming growth factor beta-like stimulated clone (TSC)22D4 as a key driver of insulin resistance and glucose intolerance in obesity and type 2 diabetes, we generated a TSC22D4-hepatocyte specific knockout line (TSC22D4-HepaKO) and exposed mice to control or NASH diet models. Mechanistic insights were generated by metabolic phenotyping and single cell liver sequencing. ResultsHepatic TSC22D4 expression was significantly correlated with markers of liver disease progression and fibrosis in both murine and human livers. Indeed, hepatic TSC22D4 levels were elevated in human NASH patients as well as in several murine NASH models. Specific genetic deletion of TSC22D4 in hepatocytes led to reduced liver lipid accumulation, improvements in steatosis and inflammation scores and decreased apoptosis in mice. Single cell RNA sequencing revealed a distinct gene signature identifying an upregulation of mitochondrial-related processes. An enrichment of genes involved in the TCA cycle, mitochondrial organization, and triglyceride metabolism underscored the hepatocyte-protective phenotype and overall decreased liver damage as seen in mouse models. ConclusionsTogether, our data uncover a new connection between targeted depletion of TSC22D4 and intrinsic metabolic processes in progressive liver disease. Cell-specific reduction of TSC22D4 improves hepatic steatosis, inflammation and promotes hepatocyte survival thus paving the way for further preclinical therapy developments.

physiology↗

bioRxiv2021

TSC22D4 interacts with Akt1 in response metabolic and stress signals

Transforming Growth Factor {beta} 1 Stimulated Clone 22 D4 (TSC22D4) is an intrinsically disordered protein that regulates cellular and physiological processes such as cell proliferation, cellular senescence as well as hepatic glucose and lipid metabolism. The molecular mechanism of TSC22D4 action in these cellular and metabolic functions, however, remains largely elusive. Here, we identified TSC22D4 as a novel protein kinase B/Akt1 interacting protein, a critical mediator of insulin/PI3K signaling pathway implicated in diverse set of diseases including type 2 diabetes, obesity and cancer. TSC22D4 interacts with Akt1 not constitutively but rather in a regulatory manner. While glucose and insulin stimulation of cells or refeeding of mice impair the hepatic TSC22D4-Akt1 interaction, inhibition of mitochondria and oxidative stress, promote it; indicating that extra- and intra-cellular cues play a key role in controlling TSC22D4-Akt1 interaction. Our results also demonstrate that together with its dimerization domain, i.e. the TSC box, TSC22D4 requires its intrinsically disordered region (D2 domain) to interact with Akt1. To understand regulation of TSC22D4 function further, we employed tandem mass spectrometry and identified 15 novel phosphorylation sites on TSC22D4. Similar to TSC22D4-Akt1 interaction, TSC22D4 phosphorylation also responds to environmental signals such as starvation, mitochondrial inhibition and oxidative stress. Interestingly, 6 out of the 15 novel phosphorylation sites lie within the TSC22D4 D2 domain, which is required for TSC22D4-Akt1 interaction. Characterization of the regulation and function of these novel phosphorylation sites, in the future, will shed light on our understanding of the role of TSC22D4-Akt1 interaction in both cell biological and physiological functions. Overall, our findings postulate a model whereby TSC22D4 acts as an environmental sensor and interacts with Akt1 to regulate cell proliferation, cellular senescence as well as maintain metabolic homeostasis.

molecular biology↗

bioRxiv2021

Induction of mitochondrial heat shock proteins and mitochondrial biogenesis in endothelial cells upon acute methylglyoxal stress: Evidence for hormetic autofeedback

Increased metabolic flux produces potentially harmful side-products, such as reactive dicarbonyl and oxygen species. The reactive dicarbonly methylglyoxal (MG) can impair oxidative capacity, which is downregulated in type 2 diabetes. Heat shock proteins (HSPs) of subfamily A (Hsp70s) promote ATP-dependent processing of damaged proteins during MG exposure which also involve mitochondrial proteins. Since the protection of mitochondrial proteins could promote higher production of reactive metabolites due to increased substrate flux, tight regulation of HspA-mediated protein handling is important. We hypothesized that stress-inducible HspAs (HspA1A/HspA1B) are pivotal for maintaining mitochondrial biogenesis during acute MG-stress. To analyze the role of stress-inducible HspA1A/HspA1B for maintenance of mitochondrial homeostasis during acute MG exposure, we knocked out HSPA1A/HSPA1B in mouse endothelial cells. HSPA1A/HSPA1B KO cells showed upregulation of the mitochondrial chaperones HspA9 (mitochondrial Hsp70/mortalin) and HspD1 (Hsp60) as well as induction of mitochondrial biogenesis upon MG exposure. Increased mitochondrial biogenesis was reflected by elevated mitochondrial branching, total count and area as well as by upregulation of mitochondrial proteins and corresponding transcription factors. Our findings suggest that mitochondrial HspA9 and HspD1 promote mitochondrial biogenesis during acute MG stress, which is counterregulated by HspA1A/HspA1B to prevent mitochondrial overstimulation and to maintain balanced oxidative capacity under metabolic stress conditions. These data support an important role of HSPs in MG-induced hormesis.

cell biology↗

bioRxiv2021

Methylglyoxal Induces Endothelial Dysfunction via Stunning

Elevated levels of methylglyoxal (MG) and its associated post-translational modifications have been reported to be associated with progression and development of numerous pathological conditions. Despite such extensive evidence, it still remains unclear what the specific effects of MG are other than that induction of cytotoxicity. Here we evaluated the effects of MG in cardiac endothelial cells in vitro. We found that MG leads to a non-proliferative state and endothelial dysfunction, which is reversible as MG-H1, a major post-translational modification induced by MG, is turned over by lysosomal degradation. MG-induced cellular stunning/paralysis describes a new hallmark for cellular dysfunction which could lead to alterations in tissue homeostasis as well as cell-to-cell interactions, thereby contributing to the pathogenesis of diseases.

cell biology↗

bioRxiv2021

The obesity-linked human lncRNA AATBC regulates adipocyte plasticity by stimulating mitochondrial dynamics and respiration

Adipocytes are critical regulators of metabolism and energy balance. While white adipocyte dysfunction is a hallmark of obesity-associated disorders, the activation of thermogenic brown and beige adipocytes is linked to improved cardiometabolic health. As adipocytes dynamically adapt to environmental cues by functionally switching between white and thermogenic phenotypes, a molecular understanding of this adipocyte plasticity could help improving energy balance and weight loss. Here, we show that the long non-coding RNA (lncRNA) Apoptosis associated transcript in bladder cancer (AATBC) is a human-specific regulator of adipocyte plasticity. Searching for new human lncRNAs implicated in adipocyte biology we compared transcriptional profiles of human adipose tissues and cultured adipocytes and discovered that AATBC was enriched in thermogenic conditions. Using primary human adipocytes and immortalized human adipocytes we found that gain-of-function of AATBC enhanced the thermogenic phenotype whereas loss-of-function diminished this effect. The AATBC-mediated increase in mitochondrial respiration was linked to a more fragmented mitochondrial network and vice versa. While we found that AATBC is predominantly located in the nucleus, its effect on global transcription was only marginal. As AATBC is specific to humans, we expressed AATBC in adipose tissue of mice to study its systemic impact, which led to lower plasma leptin levels. Interestingly, this association was also present in human subjects, as AATBC in adipose tissue was inversely correlated with plasma leptin levels, body mass index and other measures of metabolic health. In conclusion, AATBC is a novel obesity-linked regulator of adipocyte plasticity and mitochondrial function in humans.

molecular biology↗

bioRxiv2021

Semaphorin 3C exacerbates liver fibrosis

Background & AimsChronic liver disease is a growing epidemic leading to fibrosis and cirrhosis. TGF-{beta} is the pivotal pro-fibrogenic cytokine which activates hepatic stellate cells (HSC), yet, other molecules can substantially modulate TGF-{beta} signaling in the course of liver fibrosis. Expression of the axon guidance molecules Semaphorins (SEMAs), which signal through Plexins and Neuropilins (NRPs), have been associated with liver fibrosis in HBV-induced chronic hepatitis. This study aims at determining their function in the regulation of HSCs. Approach & ResultsWe analyzed publicly available patient databases and liver biopsies. We employed transgenic mice where genes are deleted only in activated HSCs to perform ex vivo analysis and animal models. SEMA3C is the most enriched member of the Semaphorin family in liver samples from cirrhotic patients. Higher expression of SEMA3C in patients with NASH, alcoholic hepatitis or HBV-induced hepatitis discriminates those with a more pro-fibrotic transcriptomic profile. SEMA3C expression is also elevated in different mouse models of liver fibrosis and in isolated HSCs upon activation. In keeping with this, deletion of SEMA3C in activated HSCs reduces myofibroblast marker expression. Conversely, SEMA3C overexpression exacerbates TGF-{beta}-mediated myofibroblast activation, as shown by increased SMAD2 phosphorylation and target gene expression. Among SEMA3C receptors, only NRP2 expression is maintained upon activation of isolated HSCs. Interestingly, lack of NRP2 in those cells reduces myofibroblast marker expression. Finally, deletion of either SEMA3C or NRP2, specifically in activated HSCs, reduces liver fibrosis in mice. ConclusionSEMA3C is a novel marker for activated HSCs that plays a fundamental role in the acquisition of the myofibroblastic phenotype and liver fibrosis.

pathology↗

bioRxiv2020

An endocrine-hepato-muscular metabolic cycle links skeletal muscle atrophy and hyperglycemia in type 2 diabetes

Both obesity and sarcopenia are frequently associated in ageing, and together may promote the progression of related conditions such as diabetes and frailty. However, little is known about the pathophysiological mechanisms underpinning this association. Here we uncover dysregulated systemic alanine metabolism and hyper-expression of the alanine transaminases (ALT) in the liver of obese/diabetic mice and humans. Hepatocyte-selective silencing of both ALT enzymes revealed a clear role in systemic alanine clearance which related to glycemic control. In obese/diabetic mice, not only did silencing both ALT enzymes retard hyperglycemia, but also reversed skeletal muscle atrophy. This was due to a rescue of depressed skeletal muscle protein synthesis, with a liver-skeletal muscle amino acid metabolic crosstalk exemplified by ex vivo experiments. Mechanistically, chronic liver glucocorticoid and glucagon signaling driven liver alanine catabolism promoted hyperglycemia and skeletal muscle wasting. Taken together, here we reveal an endocrine-hepato-muscular metabolic cycle linking hyperglycemia and skeletal muscle atrophy in type 2 diabetes.

physiology↗

bioRxiv2020

HAND2 is a novel obesity-linked adipogenic transcription factor regulated by glucocorticoid signaling

Adipocytes are critical cornerstones of energy metabolism. While obesity-induced adipocyte dysfunction is associated with insulin resistance and systemic metabolic disturbances, adipogenesis, the formation of new adipocytes and healthy adipose tissue expansion are associated with metabolic benefits. Understanding the molecular mechanisms governing adipogenesis is of great clinical potential to efficiently restore metabolic health in obesity. Here we show that Heart- and neural crest derivatives-expressed protein 2 (HAND2) is an obesity-linked adipocyte transcription factor regulated by glucocorticoids and required for adipocyte differentiation in vitro. In a large cohort of humans with obesity, white adipose tissue (WAT) HAND2 expression was correlated to body-mass-index (BMI). The HAND2 gene was enriched in white adipocytes, induced early in differentiation and responded to dexamethasone, a typical glucocorticoid receptor (GR, encoded by NR3C1) agonist. Silencing of NR3C1 in human multipotent adipose-derived stem cells (hMADS) or deletion of GR in a transgenic conditional mouse model results in diminished HAND2 expression, establishing that adipocyte HAND2 is regulated by glucocorticoids via GR in vitro and in vivo. Using a combinatorial RNAseq approach we identified gene clusters regulated by the GR-HAND2 pathway. Interestingly, silencing of HAND2 impaired adipocyte differentiation in hMADS and primary mouse adipocytes. However, a conditional adipocyte Hand2 deletion mouse model using Cre under control of the Adipoq promoter did not mirror these effects on adipose tissue differentiation, indicating that Hand2 was required at stages prior to Adipoq expression. In summary, our study identifies HAND2 as a novel obesity-linked adipocyte transcription factor, highlighting new mechanisms of GR-dependent adipogenesis in human and mice.

molecular biology↗