CD36 aggravates podocyte injury by activating NLRP3 inflammasome and inhibiting autophagy in lupus nephritis

New insight in treating autoimmune diseases by targeting autophagy

Autophagy is a highly conserved biological process in eukaryotes, which degrades cellular misfolded proteins, damaged organelles and invasive pathogens in the lysosome-dependent manner. Autoimmune diseases caused by genetic elements, environments and aberrant immune responses severely impact patients' living quality and even threaten life. Recently, numerous studies have reported autophagy can regulate immune responses, and play an important role in autoimmune diseases. In this review, we summarised the features of autophagy and autophagy-related genes, enumerated some autophagy-related genes involved in autoimmune diseases, and further overviewed how to treat autoimmune diseases through targeting autophagy. Finally, we outlooked the prospect of relieving and curing autoimmune diseases by targeting autophagy pathway.

The role of innate lymphoid cells in systemic lupus erythematosus

Systemic lupus erythematosus (SLE) is a connective tissue disorder that affects various body systems. Both the innate and adaptive immunity contribute to the onset and progression of SLE. The main mechanism of SLE is an excessive immune response of immune cells to autoantigens, which leads to systemic inflammation and inflammation-induced organ damage. Notably, a subset of innate immune cells known as innate lymphoid cells (ILCs) has recently emerged. ILCs are pivotal in the early stages of infection; participate in immune responses, inflammation, and tissue repair; and regulate the immune function of the body by resisting pathogens and regulating autoimmune inflammation and metabolic homeostasis. Thus, ILCs dysfunction can lead to autoimmune diseases. This review discusses the maturation of ILCs, the potential mechanisms by which ILCs exacerbate SLE pathogenesis, and their contributions to organ inflammatory deterioration in SLE.

Mito-Tempo alleviates ox-LDL-provoked foam cell formation by regulating Nrf2/NLRP3 signaling

Our previous studies have demonstrated that Mito-Tempol (also known as 4-hydroxy-Tempo), a mitochondrial reactive oxygen species scavenger, alleviates oxidized low-density lipoprotein (ox-LDL)-triggered foam cell formation. Given the effect of oxidative stress on activating the NOD-, LRR-, and pyrin domain-containing 3 (NLRP3) inflammasome, which promotes foam cell formation, we aimed to explore whether Mito-Tempo inhibits ox-LDL-triggered foam cell formation by regulating NLRP3 inflammasome. The results revealed that Mito-Tempo re-activated Nrf2 and alleviated macrophage foam cell formation induced by ox-LDL, whereas the effects were reversed by ML385 (a specific Nrf2 inhibitor). Mito-Tempo restored the expression and nuclear translocation of Nrf2 by decreasing ox-LDL-induced ubiquitination. Furthermore, Mito-Tempo suppressed ox-LDL-triggered NLRP3 inflammasome activation and subsequent pyroptosis, whereas the changes were blocked by ML385. Mito-Tempo decreased lipoprotein uptake by inhibiting CD36 expression and suppressed foam cell formation by regulating the NLRP3 inflammasome. Taken together, Mito-Tempo exhibits potent anti-atherosclerotic effects by regulating Nrf2/NLRP3 signaling.

The role of mitochondrial dysfunction in kidney injury and disease

Mitochondria are the main sites of aerobic respiration in the cell and mainly provide energy for the organism, and play key roles in adenosine triphosphate (ATP) synthesis, metabolic regulation, and cell differentiation and death. Mitochondrial dysfunction has been identified as a contributing factor to a variety of diseases. The kidney is rich in mitochondria to meet energy needs, and stable mitochondrial structure and function are essential for normal kidney function. Recently, many studies have shown a link between mitochondrial dysfunction and kidney disease, maintaining mitochondrial homeostasis has become an important target for kidney therapy. In this review, we integrate the role of mitochondrial dysfunction in different kidney diseases, and specifically elaborate the mechanism of mitochondrial reactive oxygen species (mtROS), autophagy and ferroptosis involved in the occurrence and development of kidney diseases, providing insights for improved treatment of kidney diseases.

Metabolism and bioenergetics in the pathophysiology of organ fibrosis

Fibrosis is the tissue scarring characterized by excess deposition of extracellular matrix (ECM) proteins, mainly collagens. A fibrotic response can take place in any tissue of the body and is the result of an imbalanced reaction to inflammation and wound healing. Metabolism has emerged as a major driver of fibrotic diseases. While glycolytic shifts appear to be a key metabolic switch in activated stromal ECM-producing cells, several other cell types such as immune cells, whose functions are intricately connected to their metabolic characteristics, form a complex network of pro-fibrotic cellular crosstalk. This review purports to clarify shared and particular cellular responses and mechanisms across organs and etiologies. We discuss the impact of the cell-type specific metabolic reprogramming in fibrotic diseases in both experimental and human pathology settings, providing a rationale for new therapeutic interventions based on metabolism-targeted antifibrotic agents.

Podocyte-specific silencing of acid sphingomyelinase gene to abrogate hyperhomocysteinemia-induced NLRP3 inflammasome activation and glomerular inflammation

Acid sphingomyelinase (ASM) has been reported to increase tissue ceramide and thereby mediate hyperhomocysteinemia (hHcy)-induced glomerular nucleotide-binding oligomerization domain-like receptor containing pyrin domain 3 (NLRP3) inflammasome activation, inflammation, and sclerosis. In the present study, we tested whether somatic podocyte-specific silencing of Smpd1 gene (mouse ASM gene code) attenuates hHcy-induced NLRP3 inflammasome activation and associated extracellular vesicle (EV) release in podocytes and thereby suppresses glomerular inflammatory response and injury. In vivo, somatic podocyte-specific Smpd1 gene silencing almost blocked hHcy-induced glomerular NLRP3 inflammasome activation in Podocre (podocyte-specific expression of cre recombinase) mice compared with control littermates. By nanoparticle tracking analysis (NTA), floxed Smpd1 shRNA transfection was found to abrogate hHcy-induced elevation of urinary EV excretion in Podocre mice. In addition, Smpd1 gene silencing in podocytes prevented hHcy-induced immune cell infiltration into glomeruli, proteinuria, and glomerular sclerosis in Podocre mice. Such protective effects of podocyte-specific Smpd1 gene silencing were mimicked by global knockout of Smpd1 gene in Smpd1-/- mice. On the contrary, podocyte-specific Smpd1 gene overexpression exaggerated hHcy-induced glomerular pathological changes in Smpd1trg/Podocre (podocyte-specific Smpd1 gene overexpression) mice, which were significantly attenuated by transfection of floxed Smpd1 shRNA. In cell studies, we also confirmed that Smpd1 gene knockout or silencing prevented homocysteine (Hcy)-induced elevation of EV release in the primary cultures of podocyte isolated from Smpd1-/- mice or podocytes of Podocre mice transfected with floxed Smpd1 shRNA compared with WT/WT podocytes. Smpd1 gene overexpression amplified Hcy-induced EV secretion from podocytes of Smpd1trg/Podocre mice, which was remarkably attenuated by transfection of floxed Smpd1 shRNA. Mechanistically, Hcy-induced elevation of EV release from podocytes was blocked by ASM inhibitor (amitriptyline, AMI), but not by NLRP3 inflammasome inhibitors (MCC950 and glycyrrhizin, GLY). Super-resolution microscopy also showed that ASM inhibitor, but not NLRP3 inflammasome inhibitors, prevented the inhibition of lysosome-multivesicular body interaction by Hcy in podocytes. Moreover, we found that podocyte-derived inflammatory EVs (released from podocytes treated with Hcy) induced podocyte injury, which was exaggerated by T cell coculture. Interstitial infusion of inflammatory EVs into renal cortex induced glomerular injury and immune cell infiltration. In conclusion, our findings suggest that ASM in podocytes plays a crucial role in the control of NLRP3 inflammasome activation and inflammatory EV release during hHcy and that the development of podocyte-specific ASM inhibition or Smpd1 gene silencing may be a novel therapeutic strategy for treatment of hHcy-induced glomerular disease with minimized side effect.NEW & NOTEWORTHY In the present study, we tested whether podocyte-specific silencing of Smpd1 gene attenuates hyperhomocysteinemia (hHcy)-induced nucleotide-binding oligomerization domain-like receptor containing pyrin domain 3 (NLRP3) inflammasome activation and associated inflammatory extracellular vesicle (EV) release in podocytes and thereby suppresses glomerular inflammatory response and injury. Our findings suggest that acid sphingomyelinase (ASM) in podocytes plays a crucial role in the control of NLRP3 inflammasome activation and inflammatory EV release during hHcy. Based on our findings, it is anticipated that the development of podocyte-specific ASM inhibition or Smpd1 gene silencing may be a novel therapeutic strategy for treatment of hHcy-induced glomerular disease with minimized side effects.

NLRP3 inflammasome and its role in autoimmune diseases: A promising therapeutic target

The NOD-like receptor protein 3 (NLRP3) inflammasome is a protein complex that regulates innate immune responses by activating caspase-1 and the inflammatory cytokines IL-1β and IL-18. Numerous studies have highlighted its crucial role in the pathogenesis and development of inflammatory bowel disease, rheumatoid arthritis, systemic lupus erythematosus, autoimmune thyroid diseases, and other autoimmune diseases. Therefore, investigating the underlying mechanisms of NLRP3 in disease and targeted drug therapies holds clinical significance. This review summarizes the structure, assembly, and activation mechanisms of the NLRP3 inflammasome, focusing on its role and involvement in various autoimmune diseases. This review also identifies studies where the involvement of the NLRP3 inflammasome in the disease mechanism within the same disease appears contradictory, as well as differences in NLRP3-related gene polymorphisms among different ethnic groups. Additionally, the latest therapeutic advances in targeting the NLRP3 inflammasome for autoimmune diseases are outlined, and novel clinical perspectives are discussed. Conclusively, this review provides a consolidated source of information on the NLRP3 inflammasome and may guide future research efforts that have the potential to positively impact patient outcomes.

Interplay of CD36, autophagy, and lipid metabolism: insights into cancer progression

CD36, a scavenger receptor B2 that is dynamically distributed between cell membranes and organelle membranes, plays a crucial role in regulating lipid metabolism. Abnormal CD36 activity has been linked to a range of metabolic disorders, such as obesity, nonalcoholic fatty liver disease, insulin resistance and cardiovascular disease. CD36 undergoes various modifications, including palmitoylation, glycosylation, and ubiquitination, which greatly affect its binding affinity to various ligands, thereby triggering and influencing various biological effects. In the context of tumors, CD36 interacts with autophagy to jointly regulate tumorigenesis, mainly by influencing the tumor microenvironment. The central role of CD36 in cellular lipid homeostasis and recent molecular insights into CD36 in tumor development indicate the applicability of CD36 as a therapeutic target for cancer treatment. Here, we discuss the diverse posttranslational modifications of CD36 and their respective roles in lipid metabolism. Additionally, we delve into recent research findings on CD36 in tumors, outlining ongoing drug development efforts targeting CD36 and potential strategies for future development and highlighting the interplay between CD36 and autophagy in the context of cancer. Our aim is to provide a comprehensive understanding of the function of CD36 in both physiological and pathological processes, facilitating a more in-depth analysis of cancer progression and a better development and application of CD36-targeting drugs for tumor therapy in the near future.

Fibroblast growth factor 21 mitigates lupus nephritis progression via the FGF21/Irgm 1/NLRP3 inflammasome pathway

As an endocrine cytokine, fibroblast growth factor 21 (FGF21) exhibits anti-inflammatory properties. With the development of lupus nephritis (LN), which is tightly related to pathogenic factors, including inflammation and immune cell dysregulation, we explored the impact of Fibroblast Growth Factor 21 (FGF21) as well as its underlying mechanism. We induced an in vivo LN model using pristane in both wild-type C57BL/6 and FGF21 knockout (FGF21-/-) mice. LN serum obtained from 32-week-old wild-type LN mice was used to stimulate RAW264.7 and human renal tubular epithelial (HK-2) cells to mimic an in vitro LN model. Moreover, our findings revealed that FGF21-/- mice showed more severe kidney injury compared to wild-type mice, as evidenced by increased levels of renal function markers, inflammatory factors, and fibrosis markers. Notably, exogenous administration of FGF21 to wild-type LN mice markedly mitigated these adverse effects. Additionally, we used tandem mass tag (TMT)-based quantitative proteomics to detect differentially expressed proteins following FGF21 treatment. Results indicated that 121 differentially expressed proteins influenced by FGF21 were involved in biological processes such as immune response and complement activation. Significantly upregulated protein Irgm 1, coupled with modulated inflammatory response, appeared to contribute to the beneficial effects of FGF21. Furthermore, Western blot analysis demonstrated that FGF21 upregulated Irgm 1 while inhibiting nucleotide-binding oligomerization domain-like receptors family pyrin domain including 3 (NLRP3) inflammasome expression. Silencing Irgm 1, in turn, reversed FGF21's inhibitory effect on NLRP3 inflammasome. In summary, FGF21 can potentially alleviate pristane-induced lupus nephritis in mice, possibly through the FGF21/Irgm 1/NLRP3 inflammasome pathway.

IUPHAR ECR review: The cGAS-STING pathway: Novel functions beyond innate immune and emerging therapeutic opportunities

Stimulator of interferon genes (STING) is a crucial innate immune sensor responsible for distinguishing pathogens and cytosolic DNA, mediating innate immune signaling pathways to defend the host. Recent studies have revealed additional regulatory functions of STING beyond its innate immune-related activities, including the regulation of cellular metabolism, DNA repair, cellular senescence, autophagy and various cell deaths. These findings highlight the broader implications of STING in cellular physiology beyond its role in innate immunity. Currently, approximately 10 STING agonists have entered the clinical stage. Unlike inhibitors, which have a maximum inhibition limit, agonists have the potential for infinite amplification. STING signaling is a complex process that requires precise regulation of STING to ensure balanced immune responses and prevent detrimental autoinflammation. Recent research on the structural mechanism of STING autoinhibition and its negative regulation by adaptor protein complex 1 (AP-1) provides valuable insights into its different effects under physiological and pathological conditions, offering a new perspective for developing immune regulatory drugs. Herein, we present a comprehensive overview of the regulatory functions and molecular mechanisms of STING beyond innate immune regulation, along with updated details of its structural mechanisms. We discuss the implications of these complex regulations in various diseases, emphasizing the importance and feasibility of targeting the immunity-dependent or immunity-independent functions of STING. Moreover, we highlight the current trend in drug development and key points for clinical research, basic research, and translational research related to STING.

Role of ferroptosis in chronic kidney disease

Chronic kidney disease (CKD) has historically been a significant global health concern, profoundly impacting both life and well-being. In the process of CKD, with the gradual loss of renal function, the incidence of various life-threatening complications, such as cardiovascular diseases, cerebrovascular accident, infection and stroke, is also increasing rapidly. Unfortunately, existing treatments exhibit limited ability to halt the progression of kidney injury in CKD, emphasizing the urgent need to delve into the precise molecular mechanisms governing the occurrence and development of CKD while identifying novel therapeutic targets. Renal fibrosis, a typical pathological feature of CKD, plays a pivotal role in disrupting normal renal structures and the loss of renal function. Ferroptosis is a recently discovered iron-dependent form of cell death characterized by lipid peroxide accumulation. Ferroptosis has emerged as a potential key player in various diseases and the initiation of organ fibrosis. Substantial evidence suggests that ferroptosis may significantly contribute to the intricate interplay between CKD and its progression. This review comprehensively outlines the intricate relationship between CKD and ferroptosis in terms of iron metabolism and lipid peroxidation, and discusses the current landscape of pharmacological research on ferroptosis, shedding light on promising avenues for intervention. It further illustrates recent breakthroughs in ferroptosis-related regulatory mechanisms implicated in the progression of CKD, thereby providing new insights for CKD treatment. Video Abstract.

Understanding the podocyte immune responses in proteinuric kidney diseases: from pathogenesis to therapy

The glomerular filtration barrier, comprising the inner layer of capillary fenestrated endothelial cells, outermost podocytes, and the glomerular basement membrane between them, plays a pivotal role in kidney function. Podocytes, terminally differentiated epithelial cells, are challenging to regenerate once injured. They are essential for maintaining the integrity of the glomerular filtration barrier. Damage to podocytes, resulting from intrinsic or extrinsic factors, leads to proteinuria in the early stages and eventually progresses to chronic kidney disease (CKD). Immune-mediated podocyte injury is a primary pathogenic mechanism in proteinuric glomerular diseases, including minimal change disease, focal segmental glomerulosclerosis, membranous nephropathy, and lupus nephritis with podocyte involvement. An extensive body of evidence indicates that podocytes not only contribute significantly to the maintenance of the glomerular filtration barrier and serve as targets of immune responses but also exhibit immune cell-like characteristics, participating in both innate and adaptive immunity. They play a pivotal role in mediating glomerular injury and represent potential therapeutic targets for CKD. This review aims to systematically elucidate the mechanisms of podocyte immune injury in various podocyte lesions and provide an overview of recent advances in podocyte immunotherapy. It offers valuable insights for a deeper understanding of the role of podocytes in proteinuric glomerular diseases, and the identification of new therapeutic targets, and has significant implications for the future clinical diagnosis and treatment of podocyte-related disorders.

The role of inflammasomes in human diseases and their potential as therapeutic targets

Inflammasomes are large protein complexes that play a major role in sensing inflammatory signals and triggering the innate immune response. Each inflammasome complex has three major components: an upstream sensor molecule that is connected to a downstream effector protein such as caspase-1 through the adapter protein ASC. Inflammasome formation typically occurs in response to infectious agents or cellular damage. The active inflammasome then triggers caspase-1 activation, followed by the secretion of pro-inflammatory cytokines and pyroptotic cell death. Aberrant inflammasome activation and activity contribute to the development of diabetes, cancer, and several cardiovascular and neurodegenerative disorders. As a result, recent research has increasingly focused on investigating the mechanisms that regulate inflammasome assembly and activation, as well as the potential of targeting inflammasomes to treat various diseases. Multiple clinical trials are currently underway to evaluate the therapeutic potential of several distinct inflammasome-targeting therapies. Therefore, understanding how different inflammasomes contribute to disease pathology may have significant implications for developing novel therapeutic strategies. In this article, we provide a summary of the biological and pathological roles of inflammasomes in health and disease. We also highlight key evidence that suggests targeting inflammasomes could be a novel strategy for developing new disease-modifying therapies that may be effective in several conditions.

Interplay of lipid metabolism and inflammation in podocyte injury

Podocytes are critical for maintaining permselectivity of the glomerular filtration barrier, and podocyte injury is a major cause of proteinuria in various primary and secondary glomerulopathies. Lipid dysmetabolism and inflammatory activation are the distinctive hallmarks of podocyte injury. Lipid accumulation and lipotoxicity trigger cytoskeletal rearrangement, insulin resistance, mitochondrial oxidative stress, and inflammation. Subsequently, inflammation promotes the progression of glomerulosclerosis and renal fibrosis via multiple pathways. These data suggest that lipid dysmetabolism positively or negatively regulates inflammation during podocyte injury. In this review, we summarize recent advances in the understanding of lipid metabolism and inflammation, and highlight the potential association between lipid metabolism and podocyte inflammation.

Pharmacological targets at the lysosomal autophagy-NLRP3 inflammasome crossroads

Many aspects of cell homeostasis and integrity are maintained by the nucleotide-binding oligomerization domain (NOD)-like receptor (NLR) family pyrin domain-containing 3 (NLRP3) inflammasome. The NLRP3 oligomeric protein complex assembles in response to exogenous and endogenous danger signals. This inflammasome has also been implicated in the pathogenesis of a range of disease conditions, particularly chronic inflammatory diseases. Given that NLRP3 modulates autophagy, which is also a key regulator of inflammasome activity, excessive inflammation may be controlled by targeting this intersecting pathway. However, specific niche areas of NLRP3-autophagy interactions and their reciprocal regulatory mechanisms remain underexplored. Consequently, we lack treatment methods specifically targeting this pivotal axis. Here, we discuss the potential of such strategies in the context of autoimmune and metabolic diseases and propose some research avenues.

C/EBPβ isoform-specific regulation of podocyte pyroptosis in lupus nephritis-induced renal injury

As an essential factor in the prognosis of systemic lupus erythematosus (SLE), lupus nephritis (LN) can accelerate the rate at which patients with SLE can transition to chronic kidney disease or even end-stage renal disease. Podocytes now appear to be a possible direct target in LN in addition to being prone to collateral damage from glomerular capillary lesions induces by immune complexes and inflammatory processes. The NLRP3 inflammasome is regulated by CCAAT/enhancer-binding protein β (C/EBPβ), which is involved in the pathogenesis of SLE. However, the role and mechanism of C/EBPβ in LN remain unclear. In this investigation, glomerular podocytes treated with LN serum and MRL/lpr mice were employed as in vivo and in vitro models of LN, respectively. In vivo, the expression of C/EBPβ isoforms was detected in kidney specimens of humans and mice with LN. Then we assessed the effect of C/EBPβ inhibition on renal structure and function by injecting RNAi adeno-associated virus of C/EBPβ shRNA into MRL/lpr mice. In vitro, glomerular podocytes were treated with LN serum and C/EBPβ siRNA to explore the role of C/EBPβ in the activation of the AIM2 inflammasome and podocyte injury. C/EBPβ-LAP and C/EBPβ-LIP were significantly overexpressed in kidney tissue samples from LN patients and mice, and C/EBPβ inhibition significantly alleviated renal function damage and ameliorated renal structural deficiencies. Inflammatory pathways downstream from the AIM2 inflammasome could be suppressed by C/EBPβ knockdown. Furthermore, the upregulation of C/EBPβ-LAP could activate the AIM2 inflammasome and podocyte pyroptosis by binding to the promoters of AIM2 and CASPASE1 to enhance their expression, and the knockdown of AIM2 or (and) caspase-1 reversed the effects of C/EBPβ-LAP overexpression. Interestingly, C/EBPβ-LIP overexpression could transcriptionally inhibit IRAG and promote Ca2+ release-mediated activation of the AIM2 inflammasome. This finding suggests that C/EBPβ is not only involved in the regulation of the expression of key proteins of the AIM2 inflammasome but also affects the polymerization of key proteins of the AIM2 inflammasome through the regulation of Ca2+ release. In conclusion, this study provides a new idea for studying the regulatory mechanism of C/EBPβ and provides a theoretical basis for the early diagnosis and treatment of LN in the future. © 2023 The Pathological Society of Great Britain and Ireland.

SGLT2 inhibitors alleviated podocyte damage in lupus nephritis by decreasing inflammation and enhancing autophagy

OBJECTIVES

The protective role of sodium glucose cotransporter 2 (SGLT2) inhibitors in renal outcomes has been revealed by large cardiovascular outcome trials among patients with type 2 diabetes. However, the effect of SGLT2 inhibitors on lupus nephritis (LN) and its underlying mechanisms remain unknown.

METHODS

We applied empagliflozin treatment to lupus-prone MRL/lpr mice to explore the renal protective potential of SGLT2 inhibitors. An SGLT2 knockout monoclonal podocyte cell line was generated using the CRISPR/Cas9 system to examine the cellular and molecular mechanisms.

RESULTS

In MRL/lpr mice treated with empagliflozin, the levels of mouse anti-dsDNA IgG-specific antibodies, serum creatinine and proteinuria were markedly decreased. For renal pathology assessment, both the glomerular and tubulointerstitial damages were lessened by administration of empagliflozin. The levels of SGLT2 expression were increased and colocalised with decreased synaptopodin in the renal biopsy samples from patients with LN and MRL/lpr mice with nephritis. The SGLT2 inhibitor empagliflozin could alleviated podocyte injury by attenuating inflammation and enhanced autophagy by reducing mTORC1 activity. Nine patients with LN treated with SGLT2 inhibitors with more than 2 months of follow-up showed that the use of SGLT2 inhibitors was associated with a significant decrease in proteinuria from 29.6% to 96.3%. Moreover, the estimated glomerular filtration rate (eGFR) was relatively stable during the treatment with SGLT2 inhibitors.

CONCLUSION

This study confirmed the renoprotective effect of SGLT2 inhibitors in lupus mice, providing more evidence for non-immunosuppressive therapies to improve renal function in classic autoimmune kidney diseases such as LN.

No NLRP3 inflammasome activity in kidney epithelial cells, not even when the NLRP3-A350V Muckle-Wells variant is expressed in podocytes of diabetic mice

Background

The NLRP3 inflammasome integrates several danger signals into the activation of innate immunity and inflammation by secreting IL-1β and IL-18. Most published data relate to the NLRP3 inflammasome in immune cells, but some reports claim similar roles in parenchymal, namely epithelial, cells. For example, podocytes, epithelial cells critical for the maintenance of kidney filtration, have been reported to express NLRP3 and to release IL-β in diabetic kidney disease, contributing to filtration barrier dysfunction and kidney injury. We questioned this and hence performed independent verification experiments.

Methods

We studied the expression of inflammasome components in human and mouse kidneys and human podocytes using single-cell transcriptome analysis. Human podocytes were exposed to NLRP3 inflammasome agonists in vitro and we induced diabetes in mice with a podocyte-specific expression of the Muckle-Wells variant of NLRP3, leading to overactivation of the Nlrp3 inflammasome (Nphs2Cre;Nlrp3A350V) versus wildtype controls. Phenotype analysis included deep learning-based glomerular and podocyte morphometry, tissue clearing, and STED microscopy of the glomerular filtration barrier. The Nlrp3 inflammasome was blocked by feeding ß-hydroxy-butyrate.

Results

Single-cell transcriptome analysis did not support relevant NLRP3 expression in parenchymal cells of the kidney. The same applied to primary human podocytes in which NLRP3 agonists did not induce IL-1β or IL-18 secretion. Diabetes induced identical glomerulomegaly in wildtype and Nphs2Cre;Nlrp3A350V mice but hyperfiltration-induced podocyte loss was attenuated and podocytes were larger in Nphs2Cre;Nlrp3A350V mice, an effect reversible with feeding the NLRP3 inflammasome antagonist ß-hydroxy-butyrate. Ultrastructural analysis of the slit diaphragm was genotype-independent hence albuminuria was identical.

Conclusion

Podocytes express low amounts of the NLRP3 inflammasome, if at all, and do not produce IL-1β and IL-18, not even upon introduction of the A350V Muckle-Wells NLRP3 variant and upon induction of podocyte stress. NLRP3-mediated glomerular inflammation is limited to immune cells.

Modulation of the immunity and inflammation by autophagy

Autophagy, a highly conserved cellular self-degradation pathway, has emerged with novel roles in the realms of immunity and inflammation. Genome-wide association studies have unveiled a correlation between genetic variations in autophagy-related genes and heightened susceptibility to autoimmune and inflammatory diseases. Subsequently, substantial progress has been made in unraveling the intricate involvement of autophagy in immunity and inflammation through functional studies. The autophagy pathway plays a crucial role in both innate and adaptive immunity, encompassing various key functions such as pathogen clearance, antigen processing and presentation, cytokine production, and lymphocyte differentiation and survival. Recent research has identified novel approaches in which the autophagy pathway and its associated proteins modulate the immune response, including noncanonical autophagy. This review provides an overview of the latest advancements in understanding the regulation of immunity and inflammation through autophagy. It summarizes the genetic associations between variants in autophagy-related genes and a range of autoimmune and inflammatory diseases, while also examining studies utilizing transgenic animal models to uncover the in vivo functions of autophagy. Furthermore, the review delves into the mechanisms by which autophagy dysregulation contributes to the development of three common autoimmune and inflammatory diseases and highlights the potential for autophagy-targeted therapies.

Decipher the Immunopathological Mechanisms and Set Up Potential Therapeutic Strategies for Patients with Lupus Nephritis

Lupus nephritis (LN) is one of the most severe complications in patients with systemic lupus erythematosus (SLE). Traditionally, LN is regarded as an immune complex (IC) deposition disease led by dsDNA-anti-dsDNA-complement interactions in the subendothelial and/or subepithelial basement membrane of glomeruli to cause inflammation. The activated complements in the IC act as chemoattractants to chemically attract both innate and adaptive immune cells to the kidney tissues, causing inflammatory reactions. However, recent investigations have unveiled that not only the infiltrating immune-related cells, but resident kidney cells, including glomerular mesangial cells, podocytes, macrophage-like cells, tubular epithelial cells and endothelial cells, may also actively participate in the inflammatory and immunological reactions in the kidney. Furthermore, the adaptive immune cells that are infiltrated are genetically restricted to autoimmune predilection. The autoantibodies commonly found in SLE, including anti-dsDNA, are cross-reacting with not only a broad spectrum of chromatin substances, but also extracellular matrix components, including α-actinin, annexin II, laminin, collagen III and IV, and heparan sulfate proteoglycan. Besides, the glycosylation on the Fab portion of IgG anti-dsDNA antibodies can also affect the pathogenic properties of the autoantibodies in that α-2,6-sialylation alleviates, whereas fucosylation aggravates their nephritogenic activity. Some of the coexisting autoantibodies, including anti-cardiolipin, anti-C1q, anti-ribosomal P autoantibodies, may also enhance the pathogenic role of anti-dsDNA antibodies. In clinical practice, the identification of useful biomarkers for diagnosing, monitoring, and following up on LN is quite important for its treatments. The development of a more specific therapeutic strategy to target the pathogenic factors of LN is also critical. We will discuss these issues in detail in the present article.

CircRNA-02191 regulating unsaturated fatty acid synthesis by adsorbing miR-145 to enhance CD36 expression in bovine mammary gland

CD36 functions as a receptor for long-chain fatty acids, promoting the absorption and transport of long-chain unsaturated fatty acids. However, the regulatory influence of upstream circRNAs or miRNAs on its expression in cow mammary gland remains unclear. Herein, we performed high-throughput sequencing to screen for differentially expressed miRNAs and mRNAs in bovine mammary tissue during the late-lactation and the dry period to screen and conducted bioinformatics analysis to identify 420 miRNA/mRNA pairs, including miR-145/CD36. Experimental results indicate that miR-145 can directly target CD36 and inhibit its expression. Additionally, the circRNA-02191 sequence is predicted to contain a miR-145 binding site. As shown by dual luciferase reporter system detection, circRNA-02191 bound to miR-145 and its overexpression significantly reduced the expression of miR-145. Furthermore, the overexpression of miR-145 inhibited triglyceride accumulation, while circRNA-02191 enhanced the expression of the miR-145 target gene CD36. The above results indicate that circRNA-02191 can regulate triglyceride and fatty acid components by binding miR-145 and subsequently alleviating the inhibitory effect of miR-145 on the expression of CD36. Taken together, these findings present a novel approach to improve milk quality by analyzing the regulatory effect and mechanism regulating the circ02191/miR-145/CD36 pathway on fatty acid synthesis in the mammary gland of dairy cows.

Breviscapine alleviates podocyte injury by inhibiting NF-κB/NLRP3-mediated pyroptosis in diabetic nephropathy

Podocyte injury is a critical factor in the pathogenesis of diabeticnephropathy (DN). Emerging evidence has demonstrated that breviscapine (Bre) exerts a renoprotective effect on diabetic rats. However, the effects of Bre on regulating podocyte injury under high glucose (HG) conditions remain unclear. In this study, an experimental mouse model of DN was induced by intraperitoneal injections of streptozotocin (STZ) in vivo. The effects of Bre on podocyte injury were assessed using cell counting kit-8 (CCK-8) assay, TdT-mediated dUTPnick-endlabelling (TUNEL) staining, quantitative real-time PCR (qRT‒PCR) and western blot analysis. We found that renal function was significantly decreased in diabetic mice, and this effect was blocked by Bre treatment. Bre effectively increased podocyte viability and inhibited HG-induced cell apoptosis. Furthermore, Bre ameliorated HG-induced podocyte injury, as evidenced by decreased α-smooth muscle actin (α-SMA) expression and increased podocin and synaptopodin expression. Mechanistically, Bre inhibited HG-induced nuclear factorkappaB (NF-κB) signalling activation and subsequently decreased NLR family pyrin domain containing 3 (NLRP3) inflammasome activation, resulting in a decrease in pyroptosis. Pharmacological inhibition of NLRP3 decreased HG-induced podocyte injury, whereas the NLRP3 agonist abrogated the effects of Bre on inhibiting podocyte injury. In summary, these results demonstrate that Bre alleviates HG-induced podocyte injury and improves renal function in diabetic mice, at least in part by inhibiting NF-κB/NLRP3-mediated pyroptosis.

Potential therapeutic effects of natural compounds targeting autophagy to alleviate podocyte injury in glomerular diseases

Podocyte injury is a common cause of proteinuric kidney diseases. Uncontrollable progressive podocyte loss accelerates glomerulosclerosis and increases the risk of end-stage renal disease. To date, owing to the complex pathological mechanism, effective therapies for podocyte injury have been limited. Accumulating evidence supports the indispensable role of autophagy in the maintenance of podocyte homeostasis. A variety of natural compounds and their derivatives have been found to regulate autophagy through multiple targets, including promotes nuclear transfer of transcription factor EB and lysosomal repair. Here, we reviewed the recent studies on the use of natural compounds and their derivatives as autophagy regulators and discussed their potential applications in ameliorating podocyte injury. Several known natural compounds with autophagy-regulatory properties, such as quercetin, silibinin, kaempferol, and artemisinin, and their medical uses were also discussed. This review will help in improving the understanding of the podocyte protective mechanism of natural compounds and promote their development for clinical use.