Immune Regulation of the Liver Through the PCSK9/CD36 Pathway During Heart Transplant Rejection

Lipid-lowering effects of bile Arisaema polysaccharides on high-fat diet-induced hyperlipidemia: An integrated analysis of metabolomics, lipidomics and microbiome

Bile Arisaema, a traditional Chinese medicine, has been previously identified by our team to possess antipyretic properties attributed to its polysaccharide component. Recently, we have confirmed that bile Arisaema played a significantly lipid-lowering effect on hyperlipidemia rats. Building upon this discovery, the present study aimed to investigate the unexplored hypolipidemic potential of its polysaccharide component and elucidate the underlying mechanisms. A soluble polysaccharide fraction devoid of free proteins, named BAPs, was extracted from bile Arisaema using a combination of hot water extraction, alcohol precipitation, and the Sevage method. The structural characteristics of BAPs were preliminarily elucidated through monosaccharide composition analysis (mainly composed of glucose), molecular weight distribution (38.74 kDa and 2.87 kDa), and glycosyl linkage analysis via methylation. The results of animal experiment demonstrated that oral administration of BAPs (400 mg/kg/day) for four weeks significantly improved abnormal serum lipid levels, hepatic function and histopathological injury on high-fat diet-induced hyperlipidemia rats. Mechanistically, the results of high throughput sequencing indicated that BAPs intake markedly altered the hepatic and fecal metabolome and lipidome, while also modulating gut microbiota composition and improving intestinal barrier integrity. Spearman's correlation analysis unveiled closely associations between the altered microbes, lipids, metabolites and serum biochemical indicators. Western blotting and qRT-PCR analyses further confirmed that these metabolic improvements were mediated by the regulation of key genes involved in lipid metabolism. Collectively, this study demonstrated that BAP supplementation effectively improved serum lipid profiles in hyperlipidemia rats by modulating metabolic disorders and restoring gut homeostasis.

Novel insights and an updated review of metabolic syndrome in immune-mediated organ transplant rejection

Metabolic syndrome (MetS) is a group of symptoms that are characterized by abnormal changes in metabolic substances such as glucose, lipids, proteins, and bile acids. MetS is a common complication after organ transplantation and can further affect the survival and physiological function of the graft by reprograming the patient's immune environment. Additionally, MetS can influence the occurrence of post-transplant complications, such as infections. In recent years, research into the epidemiology and mechanisms of MetS has grown significantly. In this review, we summarize the mechanisms of MetS after transplantation and the mechanisms of hyperglycemia, insulin resistance, hyperlipidemia, abnormal bile acids, and abnormal amino acids on the body's immune cells as related to the effect of metabolic disorders on immune rejection after liver, kidney, heart, skin and other organ transplantation. Finally, we provide an overview of current treatment strategies and offer insights into potential future therapies for managing MetS in transplant recipients.

Identification of novel metabolism-related biomarkers of Kawasaki disease by integrating single-cell RNA sequencing analysis and machine learning algorithms

Background

The bile acid metabolism (BAM) and fatty acid metabolism (FAM) have been implicated in Kawasaki disease (KD), but their precise mechanisms remain unclear. Identifying signature cells and genes related to BAM and FAM could offer a deeper understanding of their role in the pathogenesis of KD.

Method

We analyzed the public single-cell RNA sequencing (scRNA-seq) dataset GSE1687323 to characterize the immune cell-type landscape in KD. Gene sets related to BAM and FAM were collected from the Gene Set Enrichment Analysis (GSEA) database and previous literature. We analyzed the cellular heterogeneity of BAM and FAM at the single-cell level using R packages. Through differential expressed genes (DEG) analysis, high-dimensional Weighted Correlation Network Analysis (hdWGCNA) and machine learning algorithms, we identified signature genes associated with both BAM and FAM. The cellular expression patterns of signature genes were further validated using our own scRNA-seq dataset. Finally, quantitative real-time PCR (qRT-PCR) was performed to validate the expression levels of signature genes in KD, and Receiver Operating Characteristic (ROC) curve analysis was conducted to evaluate their diagnostic potential.

Results

Enhanced BAM and FAM were detected in monocytes and natural killer (NK) cells from KD in the public scRNA-seq dataset. Our scRNA-seq data confirmed the signature genes identified by machine learning algorithms: Vimentin (VIM) and chloride intracellular channel 1 (CLIC1) were upregulated in monocytes, while integrin subunit beta 2 (ITGB2) was elevated in NK cells of KD. qRT-PCR results also validated the bioinformatic analysis. Moreover, these genes demonstrated significant diagnostic potential. In the training dataset (GSE68004), the area under the curve (AUC) values and 95% CI were as follows: VIM: 0.914 (0.863-0.966), ITGB2: 0.958 (0.925-0.991), and CLIC1: 0.985 (0.969-1). The validation dataset (GSE73461) yielded similarly robust results, with AUC values and 95% CI: VIM: 0.872 (0.811-0.934), ITGB2: 0.861 (0.795-0.928), and CLIC1: 0.893 (0.837-0.948).

Conclusion

This study successfully identified and validated VIM and CLIC1 in monocytes, as well as ITGB2 in NK cells, as novel metabolism-related genes in KD. These findings suggest that BAM and FAM may play crucial roles in KD pathogenesis. Furthermore, these signature genes hold promising potential as diagnostic biomarkers for KD.

Dapagliflozin modulates hepatic lipid metabolism through the proprotein convertase subtilisin/kexin type 9/low density lipoprotein receptor pathway

BACKGROUND

Proprotein convertase subtilisin/kexin type 9 (PCSK9) is mainly secreted by the liver, and plays a crucial role in lipid metabolism disorder. Sodium-glucose cotransporter 2 inhibitors (SGLT2i) can regulate lipid metabolism through various pathways, including reducing visceral fat accumulation, modulating serum lipoprotein levels and alleviating hepatic steatosis. However, the specific regulatory mechanisms remain unclear.

METHODS

We built a model of glucose and lipid metabolism disorder in vivo and in vitro, and explored the regulatory mechanism of dapagliflozin in regulating liver lipid metabolism.

RESULTS

We found that the SGLT2i dapagliflozin significantly reduced serum levels of PCSK9, total cholesterol (TC), low density lipoprotein cholesterol (LDL-C) in high-fat diet (HFD)-fed mice, while also improving hepatic steatosis. In vitro studies confirmed that dapagliflozin increased LDL receptor (LDLR) expression in HepG2 cells, enhancing their ability to uptake LDL-C.

CONCLUSIONS

Further mechanistic studies revealed that the hepatocyte nuclear factor-1-alpha (HNF1α)/PCSK9/LDLR signalling pathway may be involved in dapagliflozin's regulation of lipid metabolism homeostasis.

Ezetimibe mediated RPS6KA2 inhibits colorectal cancer proliferation via PCSK9/MAPK signaling pathway

To investigate the effect and molecular mechanism of ezetimibe on colorectal cancer (CRC), our study found that ezetimibe significantly inhibited the proliferation and progression of CRC. Further study showed that RPS6KA2 might be the target gene of ezetimibe treatment on CRC. RPS6KA2 expression was significantly lower in human CRC tissue samples and associated with T classification and vascular invasion of tumor cells. RPS6KA2 inhibited proliferation, migration, and invasion of CRC cells. The underlying mechanisms indicated that interaction between RPS6KA2 and PCSK9 was observed within the cytoplasmic compartment of CRC cells. RPS6KA2 suppressed PCSK9 and MAPK signaling pathway in CRC cells. BI-D1780 which is an inhibitor of RPS6KA2 increased PCSK9 and MAPK signaling pathway related proteins expression in SW620 cells. However, an inhibitor or stimulator of MAPK did not affect RPS6KA2 and PCSK9 expression, respectively. In vivo, CRC cells with RPS6KA2 or PCSK9 overexpression could inhibit or promote tumor growth and metastasis, respectively. PCSK9 promoted proliferation, migration, and invasion of CRC cells. PCSK9 expression was higher in human CRC samples and associated with N classification and TNM stage of CRC. In conclusion, our study firstly suggests that ezetimibe suppresses CRC progression by upregulating RPS6KA2 while downregulating PCSK9/MAPK signaling pathway.

Conditional knockdown of hepatic PCSK9 ameliorates high-fat diet-induced liver inflammation in mice

Instruction

Accumulating evidence has shown that proprotein convertase subtilisin/kexin type 9 (PCSK9) is associated with inflammation in the vascular system. However, the roles of PCSK9 in hepatic inflammation remain unclear. Because PCSK9 is mainly expressed in the liver and modulates lipid uptake through low-density lipoprotein receptor family members, the present study aimed to elucidate the effect of conditional knockdown of hepatic PCSK9 on hyperlipidemia-induced inflammation and the underlying mechanisms of action.

Methods

PCSK9flox/flox mice were bred with ALB-Cre+ mice to obtain hepatic PCSK9 (-/-) , PCSK9 (+/-) , and PCSK9 (+/+) mice. These mice were fed with a high-fat diet for 9 weeks to induce inflammation. The effects of conditional knockdown of hepatic PCSK9 on inflammation and the underlying mechanisms were investigated by molecular biological techniques. Moreover, the findings were verified in vitro using HepG2 cells.

Results and Discussion

Conditional knockdown of hepatic PCSK9 remarkably decreased plasma levels of total cholesterol and alleviated hyperlipidemia-induced liver injury. Mechanistically, conditional knockdown of hepatic PCSK9 significantly reduced the levels of pro-inflammatory factors by downregulating the expression of Toll-like receptors, mitogen-activated protein kinase (MAPK), and phosphoinositide-3 kinase/protein kinase B, which subsequently attenuated the expression of downstream molecules, namely nuclear factor kappa-B and activator protein-1. The related mechanisms were confirmed using lipid-loaded HepG2 cells together with PCSK9 siRNA, alirocumab (anti-PCSK9 antibody), and/or a p38-MAPK inhibitor. These findings confirmed that conditional knockdown of hepatic PCSK9 attenuates liver inflammation following hyperlipidemia induction by modulating multiple signaling pathways; this suggests that targeting PCSK9 knockdown/inhibition with appropriate agents is useful not only for treating hyperlipidemia but also for ameliorating hyperlipidemia-induced liver inflammation.

Mechanisms underlying the effects of the conditional knockdown of hepatic PCSK9 in attenuating lipopolysaccharide-induced acute liver inflammation

Proprotein convertase subtilisin/kexin type 9 (PCSK9) is known to promote hyperlipidemia primarily by inducing the degradation of the low-density lipoprotein receptor. Notably, recent studies have demonstrated that PCSK9 promotes inflammation in the vascular system, however, the roles of PCSK9 in hepatic inflammation remain unclear. As PCSK9 is primarily expressed in the liver, this study aimed to elucidate the roles of PCSK9 and the underlying mechanisms in lipopolysaccharide (LPS)-challenged hepatocytes. Next-generation sequencing analysis revealed that the conditional knockdown of hepatic PCSK9 significantly reduced the plasma levels of total cholesterol and modulated the expression of hundreds of genes. Importantly, PCSK9 knockdown attenuated hepatic inflammation by suppressing several signaling pathways related to inflammation, including the Toll-like receptor, mitogen-activated protein kinase (MAPK), and phosphoinositide-3 kinase/protein kinase B pathways. This subsequently altered the expression of nuclear factor kappa-B and activator protein 1. The underlying mechanisms were further confirmed by in vitro studies using primary hepatocytes and HepG2 cells, with a p38-MAPK inhibitor, a PCSK9 antibody, and two siRNAs against PCSK9. This study is the first to report that hepatic PCSK9 knockdown ameliorates LPS-induced acute liver inflammation via modulating multiple signaling pathways, thereby suggesting therapeutic potential of PCSK9 inhibitors in treating diseases related to hepatic inflammation.

Gene expression patterns of the LDL receptor and its inhibitor Pcsk9 in the adult zebrafish brain suggest a possible role in neurogenesis

The low-density lipoprotein receptor (LDLr) is the first member of a closely related transmembrane protein family. It is known for its involvement in various physiological processes, mainly in the regulation of lipid metabolism, especially in the brains of mammals and zebrafish. In zebrafish, two ldlr genes (ldlra and b) have been identified and their distribution in the brain is not well documented. Recently, the roles of ldlr and its inhibitor pcsk9 in regenerative process after telencephalic brain injury have been discussed. In this study, we explored the expression patterns of these genes during zebrafish development. We found that ldlra expression was detected at the end of the pharyngula period (48 hpf) and increased during the larval stage. Conversely, ldlrb expression was observed from zygotic to larval stages. Using techniques like in situ hybridization and taking advantage of transgenic fish, we demonstrated the widespread distribution of ldlra, ldlrb and pcsk9 in the brain of adult zebrafish. Specifically, these genes were expressed in neurons and neural stem cells and also at lower levels in endothelial cells. As expected, intraperitoneal injection of fluorescent-labelled LDLs resulted in their uptake by cerebral endothelial cells in a homeostatic context, whereas they diffused within the brain parenchyma after telencephalic injury. However, after intracerebroventricular injections into animals, LDL particles were not taken up by neural stem cells. In conclusion, our results provide additional evidence for LDLr expression in the brain of adult zebrafish. These results raise the question of the role of LDLr in the cholesterol/lipid imbalance in cerebral complications.

CD36 in liver diseases

Cluster of differentiation 36 (CD36) is a transmembrane glycoprotein with the ability to bind to multiple ligands and perform diverse functions. Through the recognition of long-chain fatty acids, proteins containing thrombospondin structural homology repeat domains such as thrombospondin-1, and molecules with molecular structures consistent with danger- or pathogen-associated molecular patterns, CD36 participates in various physiological and pathological processes of the body. CD36 is widely expressed in various cell types, including hepatocytes and KCs in the liver, where it plays a pivotal role in lipid metabolism, inflammation, and oxidative stress. Accumulating evidence suggests that CD36 plays a complex role in the development of nonalcoholic simple fatty liver disease and NASH and contributes to the pathogenesis of inflammatory liver injury, hepatitis B/hepatitis C, liver fibrosis, and liver cancer. This review summarizes the current understanding of the structural properties, expression patterns, and functional mechanisms of CD36 in the context of liver pathophysiology. Furthermore, the potential of CD36 as a therapeutic target for the prevention and treatment of liver diseases is highlighted.

Inhibition of PCSK9 Protects against Cerebral Ischemia‒Reperfusion Injury via Attenuating Microcirculatory Dysfunction

Proprotein convertase substilin/kexin type 9 (PCSK9), a pivotal protein regulating lipid metabolism, has been implicated in promoting microthrombotic formation and inflammatory cascades, thereby contributing to cardiovascular ischemia/reperfusion (I/R) injury. However, its involvement in cerebral I/R injury and its potential role in microcirculation protection remain unexplored. In this investigation, we utilized a middle cerebral artery occlusion/reperfusion (MCAO/R) mouse model to simulate ischemic stroke. Different concentrations of evolocumab (1, 5, 10 mg/kg, i.v.), a PCSK9 inhibitor, were administered to assess its impact. Immunofluorescence staining was employed to analyze changes in the expression of occludin, claudin-5, thrombocyte, ICAM-1, VCAM-1, and CD45, providing insights into blood-brain barrier integrity, platelet adhesion, and immune cell infiltration. Moreover, the Morris water maze and elevated plus maze were utilized to evaluate neurological and behavioral functions in MCAO/R mice, shedding light on the effects of PCSK9 inhibition. Our findings revealed a surge in plasma PCSK9 levels post-MCAO/R, peaking at 24 h post-reperfusion. Evolocumab (10 mg/kg) treatment significantly mitigated brain infarction and neurological deficits, evidenced by enhanced locomotor function and reduced post-stroke anxiety. However, it did not ameliorate cognitive impairment following MCAO/R. Additionally, evolocumab administration led to diminished leakage of evans blue solution and upregulated expression of occludin and claudin-5. Thrombocyte, ICAM-1, VCAM-1, and CD45 levels were notably reduced in the penumbral area post-evolocumab treatment. These protective effects are speculated to be mediated through the inhibition of the ERK/NF-κB pathway. The PCSK9 inhibitor evolocumab holds promise as a therapeutic agent during the acute phase of stroke, exerting its beneficial effects by modulating the ERK/NF-κB signaling pathway.

Development of a PCSK9-targeted nanoparticle vaccine to effectively decrease the hypercholesterolemia

Proprotein convertase subtilisin/kexin type 9 (PCSK9) binds to the low-density lipoprotein receptor (LDLR) and mediates its internalization and degradation, resulting in an increase in LDL cholesterol levels. Recently, PCSK9 emerged as a therapeutic target for hypercholesterolemia and atherosclerosis. In this study, we develop a PCSK9 nanoparticle (NP) vaccine by covalently conjugating the catalytic domain (aa 153-aa 454, D374Y) of PCSK9 to self-assembled 24-mer ferritin NPs. We demonstrate that the PCSK9 NP vaccine effectively induces interfering antibodies against PCSK9 and reduces serum lipids levels in both a high-fat diet-induced hypercholesterolemia model and an adeno-associated virus-hPCSK9D374Y-induced hypercholesterolemia model. Additionally, the vaccine significantly reduces plaque lesion areas in the aorta and macrophages infiltration in an atherosclerosis mouse model. Furthermore, we discover that the vaccine's efficacy relied on T follicular help cells and LDLR. Overall, these findings suggest that the PCSK9 NP vaccine holds promise as an effective treatment for hypercholesterolemia and atherosclerosis.

AVCAPIR: A Novel Procalcific PIWI-Interacting RNA in Calcific Aortic Valve Disease

BACKGROUND

Calcification of the aortic valve leads to increased leaflet stiffness and consequently results in the development of calcific aortic valve disease (CAVD). However, the underlying molecular and cellular mechanisms of calcification remain unclear. Here, we identified a novel aortic valve calcification-associated PIWI-interacting RNA (piRNA; AVCAPIR) that increases valvular calcification and promotes CAVD progression.

METHODS

Using piRNA sequencing, we identified piRNAs contributing to the pathogenesis of CAVD that we termed AVCAPIRs. High-cholesterol diet-fed ApoE-/- mice with AVCAPIR knockout were used to examine the role of AVCAPIR in aortic valve calcification (AVC). Gain- and loss-of-function assays were conducted to determine the role of AVCAPIR in the induced osteogenic differentiation of human valvular interstitial cells. To dissect the mechanisms underlying AVCAPIR-elicited procalcific effects, we performed various analyses, including an RNA pulldown assay followed by liquid chromatography-tandem mass spectrometry, methylated RNA immunoprecipitation sequencing, and RNA sequencing. RNA pulldown and RNA immunoprecipitation assays were used to study piRNA interactions with proteins.

RESULTS

We found that AVCAPIR was significantly upregulated during AVC and exhibited potential diagnostic value for CAVD. AVCAPIR deletion markedly ameliorated AVC in high-cholesterol diet-fed ApoE-/- mice, as shown by reduced thickness and calcium deposition in the aortic valve leaflets, improved echocardiographic parameters (decreased peak transvalvular jet velocity and mean transvalvular pressure gradient, as well as increased aortic valve area), and diminished levels of osteogenic markers (Runx2 and Osterix) in aortic valves. These results were confirmed in osteogenic medium-induced human valvular interstitial cells. Using unbiased protein-RNA screening and molecular validation, we found that AVCAPIR directly interacts with FTO (fat mass and obesity-associated protein), subsequently blocking its N6-methyladenosine demethylase activity. Further transcriptomic and N6-methyladenosine modification epitranscriptomic screening followed by molecular validation confirmed that AVCAPIR hindered FTO-mediated demethylation of CD36 mRNA transcripts, thus enhancing CD36 mRNA stability through the N6-methyladenosine reader IGF2BP1 (insulin-like growth factor 2 mRNA binding protein 1). In turn, the AVCAPIR-dependent increase in CD36 stabilizes its binding partner PCSK9 (proprotein convertase subtilisin/kexin type 9), a procalcific gene, at the protein level, which accelerates the progression of AVC.

CONCLUSIONS

We identified a novel piRNA that induced AVC through an RNA epigenetic mechanism and provide novel insights into piRNA-directed theranostics in CAVD.

Targeting proprotein convertase subtilisin/kexin type 9 (PCSK9): from bench to bedside

Proprotein convertase subtilisin/kexin type 9 (PCSK9) has evolved as a pivotal enzyme in lipid metabolism and a revolutionary therapeutic target for hypercholesterolemia and its related cardiovascular diseases (CVD). This comprehensive review delineates the intricate roles and wide-ranging implications of PCSK9, extending beyond CVD to emphasize its significance in diverse physiological and pathological states, including liver diseases, infectious diseases, autoimmune disorders, and notably, cancer. Our exploration offers insights into the interaction between PCSK9 and low-density lipoprotein receptors (LDLRs), elucidating its substantial impact on cholesterol homeostasis and cardiovascular health. It also details the evolution of PCSK9-targeted therapies, translating foundational bench discoveries into bedside applications for optimized patient care. The advent and clinical approval of innovative PCSK9 inhibitory therapies (PCSK9-iTs), including three monoclonal antibodies (Evolocumab, Alirocumab, and Tafolecimab) and one small interfering RNA (siRNA, Inclisiran), have marked a significant breakthrough in cardiovascular medicine. These therapies have demonstrated unparalleled efficacy in mitigating hypercholesterolemia, reducing cardiovascular risks, and have showcased profound value in clinical applications, offering novel therapeutic avenues and a promising future in personalized medicine for cardiovascular disorders. Furthermore, emerging research, inclusive of our findings, unveils PCSK9's potential role as a pivotal indicator for cancer prognosis and its prospective application as a transformative target for cancer treatment. This review also highlights PCSK9's aberrant expression in various cancer forms, its association with cancer prognosis, and its crucial roles in carcinogenesis and cancer immunity. In conclusion, this synthesized review integrates existing knowledge and novel insights on PCSK9, providing a holistic perspective on its transformative impact in reshaping therapeutic paradigms across various disorders. It emphasizes the clinical value and effect of PCSK9-iT, underscoring its potential in advancing the landscape of biomedical research and its capabilities in heralding new eras in personalized medicine.

Interorgan communication with the liver: novel mechanisms and therapeutic targets

The liver is a multifunctional organ that plays crucial roles in numerous physiological processes, such as production of bile and proteins for blood plasma, regulation of blood levels of amino acids, processing of hemoglobin, clearance of metabolic waste, maintenance of glucose, etc. Therefore, the liver is essential for the homeostasis of organisms. With the development of research on the liver, there is growing concern about its effect on immune cells of innate and adaptive immunity. For example, the liver regulates the proliferation, differentiation, and effector functions of immune cells through various secreted proteins (also known as "hepatokines"). As a result, the liver is identified as an important regulator of the immune system. Furthermore, many diseases resulting from immune disorders are thought to be related to the dysfunction of the liver, including systemic lupus erythematosus, multiple sclerosis, and heart failure. Thus, the liver plays a role in remote immune regulation and is intricately linked with systemic immunity. This review provides a comprehensive overview of the liver remote regulation of the body's innate and adaptive immunity regarding to main areas: immune-related molecules secreted by the liver and the liver-resident cells. Additionally, we assessed the influence of the liver on various facets of systemic immune-related diseases, offering insights into the clinical application of target therapies for liver immune regulation, as well as future developmental trends.

Gp78 deficiency in hepatocytes alleviates hepatic ischemia-reperfusion injury via suppressing ACSL4-mediated ferroptosis

Ferroptosis, which is driven by iron-dependent lipid peroxidation, plays an essential role in liver ischemia-reperfusion injury (IRI) during liver transplantation (LT). Gp78, an E3 ligase, has been implicated in lipid metabolism and inflammation. However, its role in liver IRI and ferroptosis remains unknown. Here, hepatocyte-specific gp78 knockout (HKO) or overexpressed (OE) mice were generated to examine the effect of gp78 on liver IRI, and a multi-omics approach (transcriptomics, proteomics, and metabolomics) was performed to explore the potential mechanism. Gp78 expression decreased after reperfusion in LT patients and mice with IRI, and gp78 expression was positively correlated with liver damage. Gp78 absence from hepatocytes alleviated liver damage in mice with IRI, ameliorating inflammation. However, mice with hepatic gp78 overexpression showed the opposite phenotype. Mechanistically, gp78 overexpression disturbed lipid homeostasis, remodeling polyunsaturated fatty acid (PUFA) metabolism, causing oxidized lipids accumulation and ferroptosis, partly by promoting ACSL4 expression. Chemical inhibition of ferroptosis or ACSL4 abrogated the effects of gp78 on ferroptosis and liver IRI. Our findings reveal a role of gp78 in liver IRI pathogenesis and uncover a mechanism by which gp78 promotes hepatocyte ferroptosis by ACSL4, suggesting the gp78-ACSL4 axis as a feasible target for the treatment of IRI-associated liver damage.