Creld2 function during unfolded protein response is essential for liver metabolism homeostasis

Development and Validation of AAV-Mediated Liver, Liver-VAT, and Liver-Brain SORT and Therapeutic Regulation of FASN in Hepatic De Novo Lipogenesis

Hepatic lipogenesis combined with elevated endoplasmic reticulum (ER) stress is central to non-alcoholic steatohepatitis (NASH). However, the therapeutic targeting of key molecules is considerably less accomplished. Adeno-associated virus (AAV)-mediated gene therapies offer a new solution for various human ailments. Comprehensive bio-functional validation studies are essential to assess the impact of AAVs in the target organ for developing both preclinical and clinical gene therapy programs. Here, we have established a robust and efficient protocol for high-titer AAV production to enable detailed Selective ORgan Targeting (SORT) of AAV1, 5, 7, and 8 in vivo. Our results for in vivo SORT showed single organ (liver) targeting by AAV8, no organ targeting by AAV1, and dual organ transduction (liver-brain and liver-VAT) by AAV5 and AAV7. Using a human dataset and preclinical murine models of NASH, we identified an inverse correlation between ER stress-triggered CRELD2 and the de novo lipogenesis driver FASN. Furthermore, liver-specific silencing of CRELD2 via AAV8-shCreld2 strongly supports the contribution of CRELD2 to de novo lipogenesis through FASN regulation. Thus, our study demonstrates a robust method for producing clinically translatable AAVs that could be readily adapted for liver and/or liver-VAT or liver-brain targeted gene therapy.

Multi-tissue gene expression profiling of cows with a genetic predisposition for low and high milk urea levels

Milk urea (MU) concentration is proposed as an indicator trait for breeding toward reduced nitrogen (N) emissions and leaching in dairy. We selected 20 German Holstein cows based on MU breeding values, with 10 cows each having low (LMUg) and high (HMUg) MU genetic predisposition. Using RNA-seq, we characterized these cows to unravel molecular pathways governing post-absorptive body N pools focusing on renal filtration and reabsorption of nitrogenous compounds, hepatic urea formation and mammary gland N excretion. While we observed minor adjustments in cellular energy metabolism in different tissues associated with different MU levels, no transcriptional differences in liver ammonia detoxification were detected, despite significant differences in MU between the groups. Differential expression of AQP3 and SLC38A2 in the kidney provides evidence for higher urea concentration in the collecting duct of LMU cows than HMU cows. The mammary gland exhibited the most significant differences, particularly in tricarboxylic acid (TCA) cycle genes, amino acid transport, tRNA binding, and casein synthesis. These findings suggest that selecting for lower MU could lead to altered urinary urea (UU) handling and changes in milk protein synthesis. However, given the genetic variability in N metabolism components, the long-term effectiveness of MU-based selection in reducing N emissions remains uncertain.

Molecular characterization of the ER stress-inducible factor CRELD2

Previously, we found by constructing various luciferase reporters that a well-conserved ATF6-binding element in the CRELD2 promoter is activated by transient ATF6 overexpression. In this study, we established ATF6-deficient and ATF4-deficient cell lines to analyze CRELD2 mRNA and protein expression together with that of other ER stress-inducible factors. Our results showed that ATF6 deficiency markedly suppressed tunicamycin (Tm)-induced expression of unglycosylated CRELD2. This reduction reflected a decrease in the CRELD2 transcription level. On the other hand, a putative ATF4-binding site in the mouse CRELD2 promoter did not respond to Tm stimulation, but ATF4 loss resulted in reductions in CRELD2 mRNA and protein expression, accompanied by a decrease in Tm-induced ATF6 expression. In contrast, transient suppression of GADD34, an ATF4 downstream factor, suppressed Tm-induced CRELD2 protein expression without a decrease in ATF6 protein expression. Furthermore, we investigated the association of CRELD2 with a well-known ERAD substrate, namely, an α1-antitripsin truncation mutant, NHK, by generating various CRELD2 and NHK constructs. Coimmunoprecipitation of these proteins was observed only when the cysteine in the CXXC motif on the N-terminal side of CRELD2 was replaced with alanine, and the interaction between the two was found to be disulfide bond-independent. Taken together, these findings indicate that CRELD2 expression is regulated by multiple factors via transcriptional and posttranscriptional mechanisms. In addition, the N-terminal structure of CRELD2, including the CXXC motif, was suggested to play a role in the association of the target proteins. In the future, the identification and characterization of factors interacting with CRELD2 will be useful for understanding protein homeostasis under various ER stress conditions.

Periodic heat waves-induced neuronal etiology in the elderly is mediated by gut-liver-brain axis: a transcriptome profiling approach

Heat stress exposure in intermittent heat waves and subsequent exposure during war theaters pose a clinical challenge that can lead to multi-organ dysfunction and long-term complications in the elderly. Using an aged mouse model and high-throughput sequencing, this study investigated the molecular dynamics of the liver-brain connection during heat stress exposure. Distinctive gene expression patterns induced by periodic heat stress emerged in both brain and liver tissues. An altered transcriptome profile showed heat stress-induced altered acute phase response pathways, causing neural, hepatic, and systemic inflammation and impaired synaptic plasticity. Results also demonstrated that proinflammatory molecules such as S100B, IL-17, IL-33, and neurological disease signaling pathways were upregulated, while protective pathways like aryl hydrocarbon receptor signaling were downregulated. In parallel, Rantes, IRF7, NOD1/2, TREM1, and hepatic injury signaling pathways were upregulated. Furthermore, current research identified Orosomucoid 2 (ORM2) in the liver as one of the mediators of the liver-brain axis due to heat exposure. In conclusion, the transcriptome profiling in elderly heat-stressed mice revealed a coordinated network of liver-brain axis pathways with increased hepatic ORM2 secretion, possibly due to gut inflammation and dysbiosis. The above secretion of ORM2 may impact the brain through a leaky blood-brain barrier, thus emphasizing intricate multi-organ crosstalk.

Updated mechanisms of MASLD pathogenesis

Metabolic dysfunction-associated steatotic liver disease (MASLD) has garnered considerable attention globally. Changing lifestyles, over-nutrition, and physical inactivity have promoted its development. MASLD is typically accompanied by obesity and is strongly linked to metabolic syndromes. Given that MASLD prevalence is on the rise, there is an urgent need to elucidate its pathogenesis. Hepatic lipid accumulation generally triggers lipotoxicity and induces MASLD or progress to metabolic dysfunction-associated steatohepatitis (MASH) by mediating endoplasmic reticulum stress, oxidative stress, organelle dysfunction, and ferroptosis. Recently, significant attention has been directed towards exploring the role of gut microbial dysbiosis in the development of MASLD, offering a novel therapeutic target for MASLD. Considering that there are no recognized pharmacological therapies due to the diversity of mechanisms involved in MASLD and the difficulty associated with undertaking clinical trials, potential targets in MASLD remain elusive. Thus, this article aimed to summarize and evaluate the prominent roles of lipotoxicity, ferroptosis, and gut microbes in the development of MASLD and the mechanisms underlying their effects. Furthermore, existing advances and challenges in the treatment of MASLD were outlined.

Thioredoxin Domain Containing 5 (TXNDC5): Friend or Foe?

This review focuses on the thioredoxin domain containing 5 (TXNDC5), also known as endoplasmic reticulum protein 46 (ERp46), a member of the protein disulfide isomerase (PDI) family with a dual role in multiple diseases. TXNDC5 is highly expressed in endothelial cells, fibroblasts, pancreatic β-cells, liver cells, and hypoxic tissues, such as cancer endothelial cells and atherosclerotic plaques. TXNDC5 plays a crucial role in regulating cell proliferation, apoptosis, migration, and antioxidative stress. Its potential significance in cancer warrants further investigation, given the altered and highly adaptable metabolism of tumor cells. It has been reported that both high and low levels of TXNDC5 expression are associated with multiple diseases, such as arthritis, cancer, diabetes, brain diseases, and infections, as well as worse prognoses. TXNDC5 has been attributed to both oncogenic and tumor-suppressive features. It has been concluded that in cancer, TXNDC5 acts as a foe and responds to metabolic and cellular stress signals to promote the survival of tumor cells against apoptosis. Conversely, in normal cells, TXNDC5 acts as a friend to safeguard cells against oxidative and endoplasmic reticulum stress. Therefore, TXNDC5 could serve as a viable biomarker or even a potential pharmacological target.

Cysteine-rich with EGF-like domains 2 (CRELD2) is an endoplasmic reticulum stress-inducible angiogenic growth factor promoting ischemic heart repair

Tissue repair after myocardial infarction (MI) is guided by autocrine and paracrine-acting proteins. Deciphering these signals and their upstream triggers is essential when considering infarct healing as a therapeutic target. Here we perform a bioinformatic secretome analysis in mouse cardiac endothelial cells and identify cysteine-rich with EGF-like domains 2 (CRELD2), an endoplasmic reticulum stress-inducible protein with poorly characterized function. CRELD2 was abundantly expressed and secreted in the heart after MI in mice and patients. Creld2-deficient mice and wild-type mice treated with a CRELD2-neutralizing antibody showed impaired de novo microvessel formation in the infarct border zone and developed severe postinfarction heart failure. CRELD2 protein therapy, conversely, improved heart function after MI. Exposing human coronary artery endothelial cells to recombinant CRELD2 induced angiogenesis, associated with a distinct phosphoproteome signature. These findings identify CRELD2 as an angiogenic growth factor and unravel a link between endoplasmic reticulum stress and ischemic tissue repair.

Multi-omic analysis of the cardiac cellulome defines a vascular contribution to cardiac diastolic dysfunction in obese female mice

Coronary microvascular dysfunction (CMD) is associated with cardiac dysfunction and predictive of cardiac mortality in obesity, especially in females. Clinical data further support that CMD associates with development of heart failure with preserved ejection fraction and that mineralocorticoid receptor (MR) antagonism may be more efficacious in obese female, versus male, HFpEF patients. Accordingly, we examined the impact of smooth muscle cell (SMC)-specific MR deletion on obesity-associated coronary and cardiac diastolic dysfunction in female mice. Obesity was induced in female mice via western diet (WD) feeding alongside littermates fed standard diet. Global MR blockade with spironolactone prevented coronary and cardiac dysfunction in obese females and specific deletion of SMC-MR was sufficient to prevent obesity-associated coronary and cardiac diastolic dysfunction. Cardiac gene expression profiling suggested reduced cardiac inflammation in WD-fed mice with SMC-MR deletion independent of blood pressure, aortic stiffening, and cardiac hypertrophy. Further mechanistic studies utilizing single-cell RNA sequencing of non-cardiomyocyte cell populations revealed novel impacts of SMC-MR deletion on the cardiac cellulome in obese mice. Specifically, WD feeding induced inflammatory gene signatures in non-myocyte populations including B/T cells, macrophages, and endothelium as well as increased coronary VCAM-1 protein expression, independent of cardiac fibrosis, that was prevented by SMC-MR deletion. Further, SMC-MR deletion induced a basal reduction in cardiac mast cells and prevented WD-induced cardiac pro-inflammatory chemokine expression and leukocyte recruitment. These data reveal a central role for SMC-MR signaling in obesity-associated coronary and cardiac dysfunction, thus supporting the emerging paradigm of a vascular origin of cardiac dysfunction in obesity.

CRELD2, endoplasmic reticulum stress, and human diseases

CRELD2, a member of the cysteine-rich epidermal growth factor-like domain (CRELD) protein family, is both an endoplasmic reticulum (ER)-resident protein and a secretory factor. The expression and secretion of CRELD2 are dramatically induced by ER stress. CRELD2 is ubiquitously expressed in multiple tissues at different levels, suggesting its crucial and diverse roles in different tissues. Recent studies suggest that CRELD2 is associated with cartilage/bone metabolism homeostasis and pathological conditions involving ER stress such as chronic liver diseases, cardiovascular diseases, kidney diseases, and cancer. Herein, we first summarize ER stress and then critically review recent advances in the knowledge of the characteristics and functions of CRELD2 in various human diseases. Furthermore, we highlight challenges and present future directions to elucidate the roles of CRELD2 in human health and disease.

Aging and aging-related diseases: from molecular mechanisms to interventions and treatments

Aging is a gradual and irreversible pathophysiological process. It presents with declines in tissue and cell functions and significant increases in the risks of various aging-related diseases, including neurodegenerative diseases, cardiovascular diseases, metabolic diseases, musculoskeletal diseases, and immune system diseases. Although the development of modern medicine has promoted human health and greatly extended life expectancy, with the aging of society, a variety of chronic diseases have gradually become the most important causes of disability and death in elderly individuals. Current research on aging focuses on elucidating how various endogenous and exogenous stresses (such as genomic instability, telomere dysfunction, epigenetic alterations, loss of proteostasis, compromise of autophagy, mitochondrial dysfunction, cellular senescence, stem cell exhaustion, altered intercellular communication, deregulated nutrient sensing) participate in the regulation of aging. Furthermore, thorough research on the pathogenesis of aging to identify interventions that promote health and longevity (such as caloric restriction, microbiota transplantation, and nutritional intervention) and clinical treatment methods for aging-related diseases (depletion of senescent cells, stem cell therapy, antioxidative and anti-inflammatory treatments, and hormone replacement therapy) could decrease the incidence and development of aging-related diseases and in turn promote healthy aging and longevity.

Ectopic clotting factor VIII expression and misfolding in hepatocytes as a cause for hepatocellular carcinoma

Hemophilia A gene therapy targets hepatocytes to express B domain deleted (BDD) clotting factor VIII (FVIII) to permit viral encapsidation. Since BDD is prone to misfolding in the endoplasmic reticulum (ER) and ER protein misfolding in hepatocytes followed by high-fat diet (HFD) can cause hepatocellular carcinoma (HCC), we studied how FVIII misfolding impacts HCC development using hepatocyte DNA delivery to express three proteins from the same parental vector: (1) well-folded cytosolic dihydrofolate reductase (DHFR); (2) BDD-FVIII, which is prone to misfolding in the ER; and (3) N6-FVIII, which folds more efficiently than BDD-FVIII. One week after DNA delivery, when FVIII expression was undetectable, mice were fed HFD for 65 weeks. Remarkably, all mice that received BDD-FVIII vector developed liver tumors, whereas only 58% of mice that received N6 and no mice that received DHFR vector developed liver tumors, suggesting that the degree of protein misfolding in the ER increases predisposition to HCC in the context of an HFD and in the absence of viral transduction. Our findings raise concerns of ectopic BDD-FVIII expression in hepatocytes in the clinic, which poses risks independent of viral vector integration. Limited expression per hepatocyte and/or use of proteins that avoid misfolding may enhance safety.

Targeting endoplasmic reticulum stress-the responder to lipotoxicity and modulator of non-alcoholic fatty liver diseases

INTRODUCTION

Endoplasmic reticulum (ER) stress occurs with aberrant lipid accumulation and resultant adverse effects and widely exists in nonalcoholic fatty liver disease (NAFLD). It triggers the unfolded protein response (UPR) to restore ER homeostasis and actively participates in NAFLD pathological processes, including hepatic steatosis, inflammation, hepatocyte death, and fibrosis. Such acknowledges drive the discovery of novel NAFLD biomarker and therapeutic targets and the development of ER-stress targeted NAFLD drugs.

AREAS COVERED

This article discusses and updates the role of ER stress and UPR in NAFLD, the underlying action mechanism, and especially their full participation in NAFLD pathophysiology. It characterizes key molecular targets useful for the prevention and treatment of NAFLD and highlights the recent ER stress-targeted therapeutic strategies for NAFLD.

EXPERT OPINION

Targeting ER Stress is a valuable and promising strategy for NAFLD treatment, but its smooth translation into clinical application still requires better clarification of the different UPR patterns in diverse NAFLD physiological states. Further understanding of the distinct effects of these various patterns on NAFLD, the thresholds deciding their final impacts, and their actions via non-liver tissues and cells would be of great help to develop a precise and effective therapy for NAFLD. [Figure: see text].

Mechanism of hydroxysafflor yellow A on acute liver injury based on transcriptomics

Objective: To investigate how Hydroxysafflor yellow A (HSYA) effects acute liver injury (ALI) and what transcriptional regulatory mechanisms it may employ.

Methods: Rats were randomly divided into five groups (n = 10): Control, Model, HSYA-L, HSYA-M, and HSYA-H. In the control and model groups, rats were intraperitoneally injected with equivalent normal saline, while in the HSYA groups, they were also injected with different amounts of HSYA (10, 20, and 40 mg/kg/day) once daily for eight consecutive days. One hour following the last injection, the control group was injected into the abdominal cavity with 0.1 ml/100 g of peanut oil, and the other four groups got the same amount of a peanut oil solution containing 50% CCl4. Liver indexes were detected in rats after dissection, and hematoxylin and eosin (HE) dyeing was utilized to determine HSYA’s impact on the liver of model rats. In addition, with RNA-Sequencing (RNA-Seq) technology and quantitative real-time PCR (qRT-PCR), differentially expressed genes (DEGs) were discovered and validated. Furthermore, we detected the contents of anti-superoxide anion (anti-O2−) and hydrogen peroxide (H2O2), and verified three inflammatory genes (Icam1, Bcl2a1, and Ptgs2) in the NF-kB pathway by qRT-PCR.

Results: Relative to the control and HSYA groups, in the model group, we found 1111 DEGs that were up-/down-regulated, six of these genes were verified by qRT-PCR, including Tymp, Fabp7, Serpina3c, Gpnmb, Il1r1, and Creld2, indicated that these genes were obviously involved in the regulation of HSYA in ALI model. Membrane rafts, membrane microdomains, inflammatory response, regulation of cytokine production, monooxygenase activity, and iron ion binding were significantly enriched in GO analysis. KEGG analysis revealed that DEGs were primarily enriched for PPAR, retinol metabolism, NF-kB signaling pathways, etc. Last but not least, compared with the control group, the anti-O2− content was substantially decreased, the H2O2 content and inflammatory genes (Icam1, Bcl2a1, and Ptgs2) levels were considerably elevated in the model group. Compared with the model group, the anti-O2− content was substantially increased, the H2O2 content and inflammatory genes (Icam1, Bcl2a1, and Ptgs2) levels were substantially decreased in the HSYA group (p < 0.05).

Conclusion: HSYA could improve liver function, inhibit oxidative stress and inflammation, and improve the degree of liver tissue damage. The RNA-Seq results further verified that HSYA has the typical characteristics of numerous targets and multiple pathway. Protecting the liver from damage by regulating the expression of Tymp, Fabp7, Serpina3c, Gpnmb, Il1r1, Creld2, and the PPAR, retinol metabolism, NF-kappa B signaling pathways.

The ER protein Creld regulates ER-mitochondria contact dynamics and respiratory complex 1 activity

Dynamic contacts are formed between endoplasmic reticulum (ER) and mitochondria that enable the exchange of calcium and phospholipids. Disturbed contacts between ER and mitochondria impair mitochondrial dynamics and are a molecular hallmark of Parkinson's disease, which is also characterized by impaired complex I activity and dopaminergic neuron degeneration. Here, we analyzed the role of cysteine-rich with EGF-like domain (Creld), a poorly characterized risk gene for Parkinson's disease, in the regulation of mitochondrial dynamics and function. We found that loss of Creld leads to mitochondrial hyperfusion and reduced ROS signaling in Drosophila melanogaster, Xenopus tropicalis, and human cells. Creld fly mutants show differences in ER-mitochondria contacts and reduced respiratory complex I activity. The resulting low-hydrogen peroxide levels are linked to disturbed neuronal activity and lead to impaired locomotion, but not neurodegeneration, in Creld mutants. We conclude that Creld regulates ER-mitochondria communication and thereby hydrogen peroxide formation, which is required for normal neuron function.