Complement C5 activation promotes type 2 diabetic kidney disease via activating STAT3 pathway and disrupting the gut-kidney axis

The role of complement in kidney disease: conclusions from a Kidney Disease: Improving Global Outcomes (KDIGO) Controversies Conference

Uncontrolled complement activation can cause or contribute to glomerular injury in multiple kidney diseases. Although complement activation plays a causal role in atypical hemolytic uremic syndrome and C3 glomerulopathy, over the past decade, a rapidly accumulating body of evidence has shown a role for complement activation in multiple other kidney diseases, including diabetic nephropathy and several glomerulonephritides. The number of available complement inhibitor therapies has also increased during the same period. In 2022, Kidney Diseases: Improving Global Outcomes (KDIGO) convened a Controversies Conference, "The Role of Complement in Kidney Disease," to address the expanding role of complement dysregulation in the pathophysiology, diagnosis, and management of various glomerular diseases, diabetic nephropathy, and other forms of hemolytic uremic syndrome. Conference participants reviewed the evidence for complement playing a primary causal or secondary role in progression for several disease states and considered how evidence of complement involvement might inform management. Participating patients with various complement-mediated diseases and caregivers described concerns related to life planning, implications surrounding genetic testing, and the need for inclusive implementation of effective novel therapies into clinical practice. The value of biomarkers in monitoring disease course and the role of the glomerular microenvironment in complement response were examined, and key gaps in knowledge and research priorities were identified.

Complement anaphylatoxins: Potential therapeutic target for diabetic kidney disease

Diabetic kidney disease (DKD) is the most common cause of kidney failure, characterized by chronic inflammation and fibrosis. The complement system is increasingly implicated in the development and progression of diabetic nephropathy. The important complement anaphylatoxins C3a and C5a are key mediators of the innate immune system, which regulates cellular inflammation, oxidative stress, mitochondrial homeostasis and tissue fibrosis. This review summarizes the involvement of anaphylatoxins in the pathogenesis of diabetic kidney disease, highlights their important roles in the pathophysiologic changes of glomerulopathy, tubulointerstitial damage and immune cell infiltration, and discusses the modulatory effects of new anti-diabetic drugs acting on the complement system. Based on available clinical data and findings from the preclinical studies of complement blockade, anaphylatoxin-targeted therapeutics may become a promising approach for patients with DKD in the future.

Kidney tea [Orthosiphon aristatus (Blume) Miq.] improves diabetic nephropathy via regulating gut microbiota and ferroptosis

Introduction

Diabetic nephropathy (DN) is the leading cause of end-stage renal disease. Due to its complex pathogenesis, new therapeutic agents are urgently needed. Orthosiphon aristatus (Blume) Miq., commonly known as kidney tea, is widely used in DN treatment in China. However, the mechanisms have not been fully elucidated.

Methods

We used db/db mice as the DN model and evaluated the efficacy of kidney tea in DN treatment by measuring fasting blood glucose (FBG), serum inflammatory cytokines, renal injury indicators and histopathological changes. Furthermore, 16S rDNA gene sequencing, untargeted serum metabolomics, electron microscope, ELISA, qRT-PCR, and Western blotting were performed to explore the mechanisms by which kidney tea exerted therapeutic effects.

Results

Twelve polyphenols were identified from kidney tea, and its extract ameliorated FBG, inflammation and renal injury in DN mice. Moreover, kidney tea reshaped the gut microbiota, reduced the abundance of Muribaculaceae, Lachnoclostridium, Prevotellaceae_UCG-001, Corynebacterium and Akkermansia, and enriched the abundance of Alloprevotella, Blautia and Lachnospiraceae_NK4A136_group. Kidney tea altered the levels of serum metabolites in pathways such as ferroptosis, arginine biosynthesis and mTOR signaling pathway. Importantly, kidney tea improved mitochondrial damage, increased SOD activity, and decreased the levels of MDA and 4-HNE in the renal tissues of DN mice. Meanwhile, this functional tea upregulated GPX4 and FTH1 expression and downregulated ACSL4 and NCOA4 expression, indicating that it could inhibit ferroptosis in the kidneys.

Conclusion

Our findings imply that kidney tea can attenuate DN development by modulating gut microbiota and ferroptosis, which presents a novel scientific rationale for the clinical application of kidney tea.

C5a-C5aR1 axis controls mitochondrial fission to promote podocyte injury in lupus nephritis

Podocytes are essential to maintaining the integrity of the glomerular filtration barrier, but they are frequently affected in lupus nephritis (LN). Here, we show that the significant upregulation of Drp1S616 phosphorylation in podocytes promotes mitochondrial fission, leading to mitochondrial dysfunction and podocyte injury in LN. Inhibition or knockdown of Drp1 promotes mitochondrial fusion and protects podocytes from injury induced by LN serum. In vivo, pharmacological inhibition of Drp1 reduces the phosphorylation of Drp1S616 in podocytes in lupus-prone mice. Podocyte injury is reversed when Drp1 is inhibited, resulting in the alleviation of proteinuria. Mechanistically, complement component C5a (C5a) upregulates the phosphorylation of Drp1S616 and promotes mitochondrial fission in podocytes. Moreover, the expression of C5a receptor 1 (C5aR1) is notably upregulated in podocytes in LN. C5a-C5aR1 axis-controlled phosphorylation of Drp1S616 and mitochondrial fission are substantially suppressed when C5aR1 is knocked down by siRNA. Moreover, lupus-prone mice treated with C5aR inhibitor show reduced phosphorylation of Drp1S616 in podocytes, resulting in significantly less podocyte damage. Together, this study uncovers a novel mechanism by which the C5a-C5aR1 axis promotes podocyte injury by enhancing Drp1-mediated mitochondrial fission, which could have significant implications for the treatment of LN.

Integrated 16S rRNA sequencing and metabolomic analysis reveals the potential protective mechanism of Germacrone on diabetic nephropathy in mice

Diabetic nephropathy (DN) is a severe complication of diabetes and the leading cause of end-stage renal disease and death. Germacrone (Ger) possesses anti-inflammatory, antioxidant and anti-DN properties. However, it is unclear whether the improvement in kidney damage caused by Ger in DN mice is related to abnormal compositions and metabolites of the gut microbiota. This study generates a mouse model of DN to explore the potent therapeutic ability and mechanism of Ger in renal function by 16S rRNA sequencing and untargeted fecal metabolomics. Although there is no significant change in microbiota diversity, the structure of the gut microbiota in the DN group is quite different. Serratia_marcescens and Lactobacillus_iners are elevated in the model group but significantly decreased after Ger intervention ( P<0.05). Under the treatment of Ger, no significant differences in the diversity and richness of the gut microbiota are observed. An imbalance in the intestinal flora leads to the dysregulation of metabolites, and non-targeted metabolomics data indicate high expression of stearic acid in the DN group, and oleic acid could serve as a potential marker of the therapeutic role of Ger in the DN model. Overall, Ger improves kidney injury in diabetic mice, in part potentially by reducing the abundance of Serratia_marcescens and Lactobacillus_iners, as well as regulating the associated increase in metabolites such as oleic acid, lithocholic acid and the decrease in stearic acid. Our research expands the understanding of the relationship between the gut microbiota and metabolites in Ger-treated DN. This contributes to the usage of natural products as a therapeutic approach for the treatment of DN via microbiota regulation.

Identification of hub genes associated with Helicobacter pylori infection and type 2 diabetes mellitus: A pilot bioinformatics study

BACKGROUND

Helicobacter pylori (H. pylori) infection is related to various extragastric diseases including type 2 diabetes mellitus (T2DM). However, the possible mechanisms connecting H. pylori infection and T2DM remain unknown.

AIM

To explore potential molecular connections between H. pylori infection and T2DM.

METHODS

We extracted gene expression arrays from three online datasets (GSE60427, GSE27411 and GSE115601). Differentially expressed genes (DEGs) commonly present in patients with H. pylori infection and T2DM were identified. Hub genes were validated using human gastric biopsy samples. Correlations between hub genes and immune cell infiltration, miRNAs, and transcription factors (TFs) were further analyzed.

RESULTS

A total of 67 DEGs were commonly presented in patients with H. pylori infection and T2DM. Five significantly upregulated hub genes, including TLR4, ITGAM, C5AR1, FCER1G, and FCGR2A, were finally identified, all of which are closely related to immune cell infiltration. The gene-miRNA analysis detected 13 miRNAs with at least two gene cross-links. TF-gene interaction networks showed that TLR4 was coregulated by 26 TFs, the largest number of TFs among the 5 hub genes.

CONCLUSION

We identified five hub genes that may have molecular connections between H. pylori infection and T2DM. This study provides new insights into the pathogenesis of H. pylori-induced onset of T2DM.

Polystyrene microplastics induce kidney injury via gut barrier dysfunction and C5a/C5aR pathway activation

Microplastic is an emerging environmental pollutant with potential health risks. Recent studies have shown that microplastic could impair gut homeostasis in mammals. Although it has been widely demonstrated that gut dyshomeostasis could impact renal health through the gut-kidney axis, the effects of microplastic-induced gut dyshomeostasis on renal health and underlying mechanisms are still largely unknown. In the current work, we found that polystyrene microplastics (PS-MPs) treatment impaired the gut barrier, increased urinary complement-activated product C5a levels and renal C5aR expression, leading to chronic kidney disease-related symptoms in mice. Restoring the gut barrier using an antibiotic mixture effectively alleviated PS-MPs-induced kidney injury, indicating the involvement of the gut-kidney axis in PS-MPs-induced renal injury. Moreover, it also mitigated PS-MPs-induced alterations in urinary C5a levels and renal C5aR expression, suggesting that the renal C5a/C5aR pathway might be involved in PS-MPs' impacts on the gut-kidney axis. Further experiments using a C5aR inhibitor, PMX53, verified the vital role of renal C5a/C5aR pathway activation in the development of kidney injury induced by PS-MPs. Collectively, our results suggest that PS-MPs induce kidney injury in mice by impairing the gut barrier, increasing C5a levels, and ultimately activating the renal C5a/C5aR pathway, highlighting the crucial role of the gut-kidney axis in PS-MPs-induced kidney injury.

Expansion of Anticomplement Therapy Indications from Rare Genetic Disorders to Common Kidney Diseases

Complement constitutes a major part of the innate immune system. The study of complement in human health has historically focused on infection risks associated with complement protein deficiencies; however, recent interest in the field has focused on overactivation of complement as a cause of immune injury and the development of anticomplement therapies to treat human diseases. The kidneys are particularly sensitive to complement injury, and anticomplement therapies for several kidney diseases have been investigated. Overactivation of complement can result from loss-of-function mutations in complement regulators; gain-of-function mutations in key complement proteins such as C3 and factor B; or autoantibody production, infection, or tissue stresses, such as ischemia and reperfusion, that perturb the balance of complement activation and regulation. Here, we provide a high-level review of the status of anticomplement therapies, with an emphasis on the transition from rare diseases to more common kidney diseases.

A Transcriptome Array-Based Approach to Link SGLT-2 and Intrarenal Complement C5 Synthesis in Diabetic Nephropathy

Diabetic nephropathy is a common microvascular complication of diabetes mellitus. It is characterized by progressive chronic kidney disease (CKD) with decline of kidney function by hyperfiltration. On a mechanistic level, activation of the complement system has been implicated in the pathogenesis of diabetic nephropathy. Therefore, here we pursued a transcriptome array-based approach to link intrarenal SGLT-2 and the synthesis of distinct complement components in diabetic nephropathy. Publicly available datasets for SLC5A2 (encoding SGLT-2) and complement system components were extracted specifically from microdissected tubulointerstitial (healthy controls: n = 31, diabetic nephropathy: n = 17) and glomerular compartments (healthy controls: n = 21, diabetic nephropathy: n = 12). First, we compared tubulointerstitial and glomerular log2SLC5A2 mRNA expression levels and confirmed a predominant synthesis within the tubulointerstitial compartment. Among various complement components and receptors, the only significant finding was a positive association between SLC5A2 and the tubulointerstitial synthesis of the complement component C5 in diabetic nephropathy (p = 0.0109). Finally, intrarenal expression of SLC5A2 was associated predominantly with pathways involved in metabolic processes. Interestingly, intrarenal complement C5 synthesis was also associated with enrichment of metabolic signaling pathways, overlapping with SLC5A2 for "metabolism" and "biological oxidations". These observations could be of relevance in the pathogenesis of diabetic nephropathy and implicate a mechanistic link between SGLT-2 and intrarenal complement synthesis.

Quantitative profiling of carboxylic compounds by gas chromatography-mass spectrometry for revealing biomarkers of diabetic kidney disease

Diabetic kidney disease (DKD), a common microvascular complication of diabetes, currently lacks specific diagnostic indicators and therapeutic targets, resulting in miss of early intervention. To profile metabolic conditions in complex and precious biological samples and screen potential biomarkers for DKD diagnosis and prognosis, a rapid, convenient and reliable quantification method for carboxyl compounds by gas chromatography-mass spectrometry (GC-MS) was established with isobutyl chloroformate derivatization. The derivatives were extracted with hexane, injected into GC-MS and quantified with selected ion monitoring mode. This method showed excellent linearity(R2 > 0.99), good recoveries (81.1%-115.5%), good repeatability (RSD < 20%) and sensitivity (LODs: 0.20-499.90 pg, LOQs: 2.00-1007.00 pg). Among the 37 carboxyl compounds analyzed, 12 metabolites in short-chain fatty acids (SCFAs) metabolism pathway and amino acid metabolism pathway were linked with DKD development and among them, 6 metabolites were associated with both development and prognosis of DKD in mice. In conclusion, a reliable, convenient and sensitive method based on isobutyl chloroformate derivatization and GC-MS analysis is established and successfully applied to quantify 37 carboxyl compounds in biological samples of mice and 12 potential biomarkers for DKD development and prognosis are screened.

Vitamin D/Vitamin D receptor mitigates cisplatin-induced acute kidney injury by down-regulating C5aR

Cisplatin (DDP) is a potent chemotherapeutic; however, it can also cause acute kidney injury (AKI). Because of the complexity of the toxicity it induces, few effective methods exist for ameliorating any form of DDP-induced AKI. Recent research has suggested that the complement system is a potential molecular target for such amelioration. In the study here, in vivo (male ICR mice) and in vitro (HK-2 cells) models of DDP-induced AKI were established to investigate the potential therapeutic effects of Vitamin D (VD) against this form of AKI. Endpoints assessed in vivo/in vitro included overall renal function, degree of renal damage, and complement receptor C5aR expression using histology, immunohistochemistry, immunofluorescence, RT-PCR, and Western blots. The data indicated that the use of VD treatment could reduce renal pathological damage along with expression of TNFα, IL-1β, IL-18, and C5aR; however, an over-expression of C5aR weakened the protective effects of VD/VD receptor (VDR) against oxidative damage and inflammatory cell infiltration. Using a luciferase reporter gene assay and ChIP analysis, it was demonstrated that C5aR was transcriptionally inhibited by VDR. In conclusion, VD/VDR could delay DDP-induced AKI by inhibiting the expression of C5aR through transcriptional regulation and reducing the production of downstream pro-inflammatory cytokines. The present study revealed the regulatory mechanism of VD/VDR in acute renal inflammation and provides new insights into its therapeutic function in DDP-induced AKI.

The potential mechanism of gut microbiota-microbial metabolites-mitochondrial axis in progression of diabetic kidney disease

Diabetic kidney disease (DKD), has become the main cause of end-stage renal disease (ESRD) worldwide. Lately, it has been shown that the onset and advancement of DKD are linked to imbalances of gut microbiota and the abnormal generation of microbial metabolites. Similarly, a body of recent evidence revealed that biological alterations of mitochondria ranging from mitochondrial dysfunction and morphology can also exert significant effects on the occurrence of DKD. Based on the prevailing theory of endosymbiosis, it is believed that human mitochondria originated from microorganisms and share comparable biological characteristics with the microbiota found in the gut. Recent research has shown a strong correlation between the gut microbiome and mitochondrial function in the occurrence and development of metabolic disorders. The gut microbiome's metabolites may play a vital role in this communication. However, the relationship between the gut microbiome and mitochondrial function in the development of DKD is not yet fully understood, and the role of microbial metabolites is still unclear. Recent studies are highlighted in this review to examine the possible mechanism of the gut microbiota-microbial metabolites-mitochondrial axis in the progression of DKD and the new therapeutic approaches for preventing or reducing DKD based on this biological axis in the future.

Ulinastatin ameliorated streptozotocin-induced diabetic nephropathy: Potential effects via modulating the components of gut-kidney axis and restoring mitochondrial homeostasis

Growing evidence supports the role of the gut-kidney axis and persistent mitochondrial dysfunction in the pathogenesis of diabetic nephropathy (DN). Ulinastatin (UTI) has a potent anti-inflammatory effect, protecting the kidney and the gut barrier in sepsis, but its effect on DN has yet to be investigated. This study aimed to assess the potential mitigating effect of UTI on DN and investigate the possible involvement of gut-kidney axis and mitochondrial homeostasis in this effect. Forty male Wistar rats were divided equally into four groups: normal; UTI-treated control; untreated DN; and UTI-treated DN. At the end of the experiment, UTI ameliorated DN by modulating the gut-kidney axis as it improved serum and urinary creatinine, urine volume, creatinine clearance, blood urea nitrogen, urinary albumin, intestinal morphology including villus height, crypt depth, and number of goblet cells, with upregulating the expression of intestinal tight-junction protein claudin-1, and counteracting kidney changes as indicated by significantly decreasing glomerular tuft area and periglomerular and peritubular collagen deposition. In addition, it significantly reduced intestinal and renal nuclear factor kappa B (NF-κB), serum Complement 5a (C5a), renal monocyte chemoattractant protein-1 (MCP-1), renal intercellular adhesion molecule 1 (ICAM1), and renal signal transducer and activator of transcription 3 (STAT3), mitochondrial dynamin related protein 1 (Drp1), mitochondrial fission 1 protein (FIS1), mitochondrial reactive oxygen species (ROS), renal hydrogen peroxide (H2O2), and 8-hydroxy-2'-deoxyguanosine (8-OHdG) levels. Furthermore, it significantly increased serum short chain fatty acids (SCFAs), and mitochondrial ATP levels and mitochondrial transmembrane potential. Moreover, there were significant correlations between measured markers of gut components of the gut-kidney axis and renal function tests in UTI-treated DN group. In conclusion, UTI has a promising therapeutic effect on DN by modulating the gut-kidney axis and improving renal mitochondrial dynamics and redox equilibrium.

Novel insights into STAT3 in renal diseases

Signal transducer and activator of transcription 3 (STAT3) is a cell-signal transcription factor that has attracted considerable attention in recent years. The stimulation of cytokines and growth factors can result in the transcription of a wide range of genes that are crucial for several cellular biological processes involved in pro- and anti-inflammatory responses. STAT3 has attracted considerable interest as a result of a recent upsurge in study because of their role in directing the innate immune response and sustaining inflammatory pathways, which is a key feature in the pathogenesis of many diseases, including renal disorders. Several pathological conditions which may involve STAT3 include diabetic nephropathy, acute kidney injury, lupus nephritis, polycystic kidney disease, and renal cell carcinoma. STAT3 is expressed in various renal tissues under these pathological conditions. To better understand the role of STAT3 in the kidney and provide a theoretical foundation for STAT3-targeted therapy for renal disorders, this review covers the current work on the activities of STAT3 and its mechanisms in the pathophysiological processes of various types of renal diseases.

JAK/STAT signaling in diabetic kidney disease

Diabetic kidney disease (DKD) is the most important microvascular complication of diabetes and the leading cause of end-stage renal disease (ESRD) worldwide. The Janus kinase/signal transducer and activator of the transcription (JAK/STAT) signaling pathway, which is out of balance in the context of DKD, acts through a range of metabolism-related cytokines and hormones. JAK/STAT is the primary signaling node in the progression of DKD. The latest research on JAK/STAT signaling helps determine the role of this pathway in the factors associated with DKD progression. These factors include the renin-angiotensin system (RAS), fibrosis, immunity, inflammation, aging, autophagy, and EMT. This review epitomizes the progress in understanding the complicated explanation of the etiologies of DKD and the role of the JAK/STAT pathway in the progression of DKD and discusses whether it can be a potential target for treating DKD. It further summarizes the JAK/STAT inhibitors, natural products, and other drugs that are promising for treating DKD and discusses how these inhibitors can alleviate DKD to explore possible potential drugs that will contribute to formulating effective treatment strategies for DKD in the near future.

C5a drives the inflammatory response with bacterial dose effect by binding to C5aR1 in zebrafish infected with Aeromonas hydrophila

The complement system is essential to host defense, but its excessive activation caused by severe pathogen invasion is a driving force in adverse inflammatory. The binding of complement component 5a (C5a) and complement component 5a receptor 1 (C5aR1) is the key to trigger complement-mediated inflammatory response in mammals. However, the role of C5a-C5aR1 axis in fish immune response remains obscure. In this study, the role of C5a-C5aR1 axis of zebrafish (Danio rerio) after serious infection with Aeromonas hydrophila was investigated. C5a and C5aR1 of zebrafish were cloned, with CDS sequences of 228 and 1041 bp, respectively, and they were widely expressed in various tissues with the highest expression in the liver and spleen, respectively. The survival of zebrafish was closely correlated to the dose of A. hydrophila. The cytokine storm occurred at high concentrations of A. hydrophila infection. At 24 h post infection (hpi), the expression of C5a and C5aR1 in the spleen increased 26.8-fold and 9.9-fold in treatment group 1 (TG1, 3.0 × 107 CFU/mL) (P < 0.01), and 4.7-fold and 3.4-fold in treatment group 2 (TG2, 1.0 × 107 CFU/mL) (P < 0.05), respectively. Correspondingly, proinflammatory cytokines interleukin-1β (IL-1β), interleukin-8 (IL-8), and interleukin-17 (IL-17) were positively correlated to C5a and C5aR1 at mRNA and protein expression levels. The expression of IL-1β was significantly increased in the spleen at 6 hpi, with a 599.2-fold and 203.2-fold upregulation in TG1 and TG2 (P < 0.001), respectively. Moreover, after inhibition of C5a-C5aR1 binding treated with C5aR1 antagonist (W-54011), zebrafish showed lower expression of C5a, C5aR1, and cytokines, less intestinal damage, and significantly enhancement of survival (P < 0.05) after A. hydrophila challenge. This study revealed that the inflammatory effect of C5a was achieved by binding to C5aR1 in zebrafish, providing novel insights into using C5a-C5aR1 axis as an effective target to reduce bacterial inflammation and disease in fish.

The roles of gut microbiota and its metabolites in diabetic nephropathy

Diabetic nephropathy (DN) is a severe microvascular complication of diabetes, which increases the risk of renal failure and causes a high global disease burden. Due to the lack of sustainable treatment, DN has become the primary cause of end-stage renal disease worldwide. Gut microbiota and its metabolites exert critical regulatory functions in maintaining host health and are associated with many pathogenesis of aging-related chronic diseases. Currently, the theory gut-kidney axis has opened a novel angle to understand the relationship between gut microbiota and multiple kidney diseases. In recent years, accumulating evidence has revealed that the gut microbiota and their metabolites play an essential role in the pathophysiologic processes of DN through the gut-kidney axis. In this review, we summarize the current investigations of gut microbiota and microbial metabolites involvement in the progression of DN, and further discuss the potential gut microbiota-targeted therapeutic approaches for DN.

Therapeutic Potential of Targeting Complement C5a Receptors in Diabetic Kidney Disease

Diabetic kidney disease (DKD) affects 30-40% of patients with diabetes and is currently the leading cause of end-stage renal disease (ESRD). The activation of the complement cascade, a highly conserved element of the innate immune system, has been implicated in the pathogenesis of diabetes and its complications. The potent anaphylatoxin C5a is a critical effector of complement-mediated inflammation. Excessive activation of the C5a-signalling axis promotes a potent inflammatory environment and is associated with mitochondrial dysfunction, inflammasome activation, and the production of reactive oxygen species. Conventional renoprotective agents used in the treatment of diabetes do not target the complement system. Mounting preclinical evidence indicates that inhibition of the complement system may prove protective in DKD by reducing inflammation and fibrosis. Targeting the C5a-receptor signaling axis is of particular interest, as inhibition at this level attenuates inflammation while preserving the critical immunological defense functions of the complement system. In this review, the important role of the C5a/C5a-receptor axis in the pathogenesis of diabetes and kidney injuries will be discussed, and an overview of the status and mechanisms of action of current complement therapeutics in development will be provided.

The anaphylatoxin C5a: Structure, function, signaling, physiology, disease, and therapeutics

The complement system is one of the oldest known tightly regulated host defense systems evolved for efficiently functioning cell-based immune systems and antibodies. Essentially, the complement system acts as a pivot between the innate and adaptive arms of the immune system. The complement system collectively represents a cocktail of ∼50 cell-bound/soluble glycoproteins directly involved in controlling infection and inflammation. Activation of the complement cascade generates complement fragments like C3a, C4a, and C5a as anaphylatoxins. C5a is the most potent proinflammatory anaphylatoxin, which is involved in inflammatory signaling in a myriad of tissues. This review provides a comprehensive overview of human C5a in the context of its structure and signaling under several pathophysiological conditions, including the current and future therapeutic applications targeting C5a.

Complement as a vital nexus of the pathobiological connectome for acute respiratory distress syndrome: An emerging therapeutic target

The hallmark of acute respiratory distress syndrome (ARDS) pathobiology is unchecked inflammation-driven diffuse alveolar damage and alveolar-capillary barrier dysfunction. Currently, therapeutic interventions for ARDS remain largely limited to pulmonary-supportive strategies, and there is an unmet demand for pharmacologic therapies targeting the underlying pathology of ARDS in patients suffering from the illness. The complement cascade (ComC) plays an integral role in the regulation of both innate and adaptive immune responses. ComC activation can prime an overzealous cytokine storm and tissue/organ damage. The ARDS and acute lung injury (ALI) have an established relationship with early maladaptive ComC activation. In this review, we have collected evidence from the current studies linking ALI/ARDS with ComC dysregulation, focusing on elucidating the new emerging roles of the extracellular (canonical) and intracellular (non-canonical or complosome), ComC (complementome) in ALI/ARDS pathobiology, and highlighting complementome as a vital nexus of the pathobiological connectome for ALI/ARDS via its crosstalking with other systems of the immunome, DAMPome, PAMPome, coagulome, metabolome, and microbiome. We have also discussed the diagnostic/therapeutic potential and future direction of ALI/ARDS care with the ultimate goal of better defining mechanistic subtypes (endotypes and theratypes) through new methodologies in order to facilitate a more precise and effective complement-targeted therapy for treating these comorbidities. This information leads to support for a therapeutic anti-inflammatory strategy by targeting the ComC, where the arsenal of clinical-stage complement-specific drugs is available, especially for patients with ALI/ARDS due to COVID-19.

Cathepsin S Knockdown Suppresses Endothelial Inflammation, Angiogenesis, and Complement Protein Activity under Hyperglycemic Conditions In Vitro by Inhibiting NF-κB Signaling

Hyperglycemia plays a key role in the development of microvascular complications, endothelial dysfunction (ED), and inflammation. It has been demonstrated that cathepsin S (CTSS) is activated in hyperglycemia and is involved in inducing the release of inflammatory cytokines. We hypothesized that blocking CTSS might alleviate the inflammatory responses and reduce the microvascular complications and angiogenesis in hyperglycemic conditions. In this study, we treated human umbilical vein endothelial cells (HUVECs) with high glucose (HG; 30 mM) to induce hyperglycemia and measured the expression of inflammatory cytokines. When treated with glucose, hyperosmolarity could be linked to cathepsin S expression; however, many have mentioned the high expression of CTSS. Thus, we made an effort to concentrate on the immunomodulatory role of the CTSS knockdown in high glucose conditions. We validated that the HG treatment upregulated the expression of inflammatory cytokines and CTSS in HUVEC. Further, siRNA treatment significantly downregulated CTSS expression along with inflammatory marker levels by inhibiting the nuclear factor-kappa B (NF-κB) mediated signaling pathway. In addition, CTSS silencing led to the decreased expression of vascular endothelial markers and downregulated angiogenic activity in HUVECs, which was confirmed by a tube formation experiment. Concurrently, siRNA treatment reduced the activation of complement proteins C3a and C5a in HUVECs under hyperglycemic conditions. These findings show that CTSS silencing significantly reduces hyperglycemia-induced vascular inflammation. Hence, CTSS may be a novel target for preventing diabetes-induced microvascular complications.

An environmentally relevant concentration of antibiotics impairs the immune system of zebrafish (Danio rerio) and increases susceptibility to virus infection

In this work, we analysed the transcriptome and metatranscriptome profiles of zebrafish exposed to an environmental concentration of the two antibiotics most frequently detected in European inland surface water, sulfamethoxazole (SMX) and clarithromycin (CLA). We found that those animals exposed to antibiotics (SMX+CLA) for two weeks showed a higher bacterial load in both the intestine and kidney; however, significant differences in the relative abundance of certain bacterial classes were found only in the intestine, which also showed an altered fungal profile. RNA-Seq analysis revealed that the complement/coagulation system is likely the most altered immune mechanism, although not the only one, in the intestine of fish exposed to antibiotics, with numerous genes inhibited compared to the control fish. On the other hand, the effect of SMX+CLA in the kidney was more modest, and an evident impact on the immune system was not observed. However, infection of both groups with spring viremia of carp virus (SVCV) revealed a completely different response to the virus and an inability of the fish exposed to antibiotics to respond with an increase in the transcription of complement-related genes, a process that was highly activated in the kidney of the untreated zebrafish after SVCV challenge. Together with the higher susceptibility to SVCV of zebrafish treated with SMX+CLA, this suggests that complement system impairment is one of the most important mechanisms involved in antibiotic-mediated immunosuppression. We also observed that zebrafish larvae exposed to SMX+CLA for 7 days showed a lower number of macrophages and neutrophils.

Platelets promote CRC by activating the C5a/C5aR1 axis via PSGL-1/JNK/STAT1 signaling in tumor-associated macrophages

Rationale: Platelets can influence the progression and prognosis of colorectal cancer (CRC) through multiple mechanisms, including crosstalk with tumor-associated macrophages (TAMs). However, the mechanisms underlying the crosstalk between platelets and TAMs remain unclear. The present study aimed to investigate the role of intratumoral platelets in regulating the function of TAMs and to identify the underlying mechanisms. Methods: The interaction of platelets with macrophages was assessed in the presence or absence of the indicated compounds in vivo. An azoxymethane/dextran sodium sulfate (AOM/DSS)-induced CRC mouse model was used to investigate the role of platelets in controlling CRC development. Multiplexed immunofluorescence staining, fluorescence-activated cell sorting (FACS), and RNA sequence analysis were used to examine the changes in TAMs. TAMs and bone marrow-derived macrophages (BMDMs) were treated with the indicated compounds or siRNA against specific targets, and the expression levels of signal transducer and activator of transcription 1 (STAT1), c-Jun N-terminal kinase (JNK), and P-selectin glycoprotein ligand-1 (PSGL-1) were measured by Western blotting. The mRNA expression levels of complement 5 (C5), complement 5a receptor 1 (C5ar1), Arginase 1 (Arg1) and Il10 were measured by real-time RT-PCR, and the complement 5a (C5a) concentration was measured by ELISA. The dual-luciferase reporter assay and ChIP assay were performed to examine the potential regulatory mechanisms of platelet induction of C5 transcription in TAMs. Results: In our study, we found that an increase in platelets exacerbated CRC development, while inhibiting platelet adhesion attenuated tumor growth. Platelets signal TAMs through P-selectin (CD62P) binding to PSGL-1 expressed on TAMs and activating the JNK/STAT1 pathway to induce the transcription of C5 and the release of C5a, shifting TAMs toward a protumor phenotype. Inhibiting the C5a/C5aR1 axis or PSGL-1 significantly reduced CRC growth. Conclusions: An increase in intratumoral platelets promoted CRC growth and metastasis by CD62P binding to PSGL-1 expressed on TAMs, leading to JNK/STAT1 signaling activation, which promoted C5 transcription and activated the C5a/C5aR1 axis in TAMs. Our study examined the mechanism of the crosstalk between platelets and TAMs to exacerbate CRC development and proposed a potential therapeutic strategy for CRC patients.

The role and mechanism of the gut microbiota in the development and treatment of diabetic kidney disease

Diabetic kidney disease (DKD) is a common complication in patients with diabetes mellitus (DM). Increasing evidence suggested that the gut microbiota participates in the progression of DKD, which is involved in insulin resistance, renin-angiotensin system (RAS) activation, oxidative stress, inflammation and immunity. Gut microbiota-targeted therapies including dietary fiber, supplementation with probiotics or prebiotics, fecal microbiota transplantation and diabetic agents that modulate the gut microbiota, such as metformin, glucagon-like peptide-1 (GLP-1) receptor agonists, dipeptidyl peptidase-4 (DPP-4) inhibitors, and sodium-glucose transporter-2 (SGLT-2) inhibitors. In this review, we summarize the most important findings about the role of the gut microbiota in the pathogenesis of DKD and the application of gut microbiota-targeted therapies.

The Complement Pathway: New Insights into Immunometabolic Signaling in Diabetic Kidney Disease

Significance: The metabolic disorder, diabetes mellitus, results in microvascular complications, including diabetic kidney disease (DKD), which is partly believe to involve disrupted energy generation in the kidney, leading to injury that is characterized by inflammation and fibrosis. An increasing body of evidence indicates that the innate immune complement system is involved in the pathogenesis of DKD; however, the precise mechanisms remain unclear. Recent Advances: Complement, traditionally thought of as the prime line of defense against microbial intrusion, has recently been recognized to regulate immunometabolism. Studies have shown that the complement activation products, Complement C5a and C3a, which are potent pro-inflammatory mediators, can mediate an array of metabolic responses in the kidney in the diabetic setting, including altered fuel utilization, disrupted mitochondrial respiratory function, and reactive oxygen species generation. In diabetes, the lectin pathway is activated via autoreactivity toward altered self-surfaces known as danger-associated molecular patterns, or via sensing altered carbohydrate and acetylation signatures. In addition, endogenous complement inhibitors can be glycated, whereas diet-derived glycated proteins can themselves promote complement activation, worsening DKD, and lending support for environmental influences as an additional avenue for propagating complement-induced inflammation and kidney injury. Critical Issues: Recent evidence indicates that conventional renoprotective agents used in DKD do not target the complement, leaving this web of inflammatory stimuli intact. Future Directions: Future studies should focus on the development of novel pharmacological agents that target the complement pathway to alleviate inflammation, oxidative stress, and kidney fibrosis, thereby reducing the burden of microvascular diseases in diabetes. Antioxid. Redox Signal. 37, 781-801.

The role and mechanisms of gut microbiota in diabetic nephropathy, diabetic retinopathy and cardiovascular diseases

Type 2 diabetes mellitus (T2DM) and T2DM-related complications [such as retinopathy, nephropathy, and cardiovascular diseases (CVDs)] are the most prevalent metabolic diseases. Intriguingly, overwhelming findings have shown a strong association of the gut microbiome with the etiology of these diseases, including the role of aberrant gut bacterial metabolites, increased intestinal permeability, and pathogenic immune function affecting host metabolism. Thus, deciphering the specific microbiota, metabolites, and the related mechanisms to T2DM-related complications by combined analyses of metagenomics and metabolomics data can lead to an innovative strategy for the treatment of these diseases. Accordingly, this review highlights the advanced knowledge about the characteristics of the gut microbiota in T2DM-related complications and how it can be associated with the pathogenesis of these diseases. Also, recent studies providing a new perspective on microbiota-targeted therapies are included.

The Complement System in Metabolic-Associated Kidney Diseases

Metabolic syndrome (MS) is a group of clinical abnormalities characterized by central or abdominal obesity, hypertension, hyperuricemia, and metabolic disorders of glucose or lipid. Currently, the prevalence of MS is estimated about 25% in general population and is progressively increasing, which has become a challenging public health burden. Long-term metabolic disorders can activate the immune system and trigger a low-grade chronic inflammation named “metaflammation.” As an important organ involved in metabolism, the kidney is inevitably attacked by immunity disequilibrium and “metaflammation.” Recently, accumulating studies have suggested that the complement system, the most important and fundamental component of innate immune responses, is actively involved in the development of metabolic kidney diseases. In this review, we updated and summarized the different pathways through which the complement system is activated in a series of metabolic disturbances and the mechanisms on how complement mediate immune cell activation and infiltration, renal parenchymal cell damage, and the deterioration of renal function provide potential new biomarkers and therapeutic options for metabolic kidney diseases.

Hypoglycaemic and anti-ageing activities of green alga Ulva lactuca polysaccharide via gut microbiota in ageing-associated diabetic mice

Ageing-related type 2 diabetes is a significant public health problem. Particularly, the number of cases and fatality rates of ageing-associated diabetes increase with population ageing. This study aimed to investigate the structural characterisation of Ulva lactuca polysaccharide (ULP) and the hypoglycaemic effect on ageing-associated diabetic mice using gut microbiota variation. Sugar residuals analysis showed that the purified ULP (ULP-1) comprised β-D-Xylp-(1→3)-β-D-Arap-(1→6)-β-D-Galp-(1→6)-β-D-Glcp linked to [→α-L-Rhap-(1→4)-β-D-GlcpA→]_n and α-D-Manp-(1→4)-α-L-Rhap(2SO₃^-)-(1→2)-α-L-Rhap(4SO₃^-)-(1→2)-α-L-Arap-(1→2)-α-L-Rhap-(1→ as its side chains at β-D-Glcp. Moreover, ULP modulated the expression levels of p16^Ink4a, MMP2, FoxO1, GLP-1/GLP-1R, STAT3, and GLUT4 to improve the status of ageing and diabetes, which was concurrent with the increased abundance of Dubosiella, Enterococcus, Romboutsia, Bifidobacterium, Kurthia, Clostridium_sensu_stricto_1, Corynebacterium, Faecalibaculum, Aerococcus and Vibrio. Notably, Dubosiella, Romboutsia, Bifidobacterium, Turicibacter and Clostridium_sensu_stricto_1 could serve as important intermediates for delaying ageing and diabetes. Additionally, the ULP-1 structure is strongly binding interaction with the target protein through hydrogen bonding and Van der Waals force, especially for GLP-1 (-10.34 kcal/mol), p16^Ink4a (-10.51 kcal/mol) and GLP-1R (-8.57 kcal/mol). Moreover, the average length of the hydrogen bond was observed to be 2.36 MPa, which is smaller than that of the traditional hydrogen bond. Therefore, ULP has the potential to function as a nutraceutical to delay or prevent the development of ageing-related type 2 diabetes.

Complement C5a induces the generation of neutrophil extracellular traps by inhibiting mitochondrial STAT3 to promote the development of arterial thrombosis

Background

Thrombotic events cannot be completely prevented by antithrombotics, implicating a therapeutic gap due to inflammation, a not yet sufficiently addressed mechanism. Neutrophil extracellular traps (NETs) are an essential interface between inflammation and thrombosis, but exactly how the NETotic process is initiated and maintained during arterial thrombosis remains incompletely understood.

Methods and results

We found that the plasma concentrations of C5a were higher in patients with ST-elevation myocardial infarction (STEMI) than in patients with angina and higher in mice with left common carotid artery (LCCA) thrombosis induced by FeCl₃ than in control mice. We observed that the thrombus area and weight were decreased and that NET formation in the thrombi was reduced in the group treated with the selective C5aR1 receptor inhibitor PMX53 compared with the NaCl group. In vitro, NETosis was observed when C5a was added to neutrophil cultures, and this effect was reversed by PMX53. In addition, our data showed that C5a increased the production of mitochondrial reactive oxygen species (ROS) and that the promotion of NET formation by C5a was mitochondrial ROS (Mito-ROS) dependent. Furthermore, we found that C5a induced the production of Mito-ROS by inhibiting mitochondrial STAT3 activity.

Conclusions

By inhibiting mitochondrial STAT3 to elicit Mito-ROS generation, C5a triggers the generation of NETs to promote the development of arterial thrombosis. Hence, our study identifies complement C5a as a potential new target for the treatment and prevention of thrombosis.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12959-022-00384-0.

Mannan-binding lectin exacerbates the severity of psoriasis by promoting plasmacytoid dendritic cell differentiation via the signal transducer and activator of transcription 3-interferon regulatory factor 8 axis

Psoriasis is a chronic inflammatory skin disease mediated by host immune responses. Plasmacytoid dendritic cells (pDC) and interferon (IFN)-α secreted by pDC are involved in the initiation of psoriasis. Mannan-binding lectin (MBL), a vital component of the complement pathway, plays a critical role in innate immune defense and the inflammatory response. Our previous study found that MBL could exacerbate skin inflammation in psoriatic mice, but the effect of MBL on pDC remains unstudied. Herein, we revealed that the circulating level of MBL was elevated in patients with psoriasis compared with the healthy controls. Moreover, the MBL level was positively correlated with disease severity, relative inflammatory cytokine levels, and peripheral blood (PB) pDC frequency in psoriasis. An in vitro study determined that the MBL protein could promote the differentiation of human pDC and upregulate the production of relative inflammatory cytokines and chemokines. Additionally, MBL-deficient (MBL^-/- ) mice exhibited decreased accumulation of pDC in lymph nodes, spleens, and skin lesions with reduced secretion of pDC-related cytokines compared with wild-type (WT) mice in the preliminary stage of psoriasis induced by imiquimod. Notably, the differentiation of pDC from bone marrow (BM) cells derived from MBL^-/- mice was weakened compared with that from WT mice upon Fms-like tyrosine kinase 3 ligand (Flt3L) incubation. Mechanistic research indicated that the signal transducer and activator of transcription 3 (STAT3)-interferon regulatory factor 8 (IRF8) axis was responsible for MBL-modulated pDC differentiation. In summary, these results suggest that MBL exacerbates the severity of psoriasis by enhancing pDC differentiation and pDC-related cytokine secretion via the STAT3-IRF8 axis, thus providing a new target for psoriasis treatment.

Pathogenesis and Clinical Significance of In-Stent Restenosis in Patients with Diabetes

Diabetes mellitus (DM) is a strong risk factor for the development of cardiovascular diseases such as coronary heart disease, cerebrovascular disease, and peripheral arterial disease (PAD). In the population of people living with DM, PAD is characterised by multi-level atherosclerotic lesions as well as greater involvement of the arteries below the knee. DM is also a factor that significantly increases the risk of lower limb amputation. Percutaneous balloon angioplasty with or without stent implantation is an important method of the treatment for atherosclerotic cardiovascular diseases, but restenosis is a factor limiting its long-term effectiveness. The pathogenesis of atherosclerosis in the course of DM differs slightly from that in the general population. In the population of people living with DM, more attention is drawn to such factors as inflammation, endothelial dysfunction, platelet dysfunction, blood rheological properties, hypercoagulability, and additional factors stimulating vascular smooth muscle cell proliferation. DM is a risk factor for restenosis. The purpose of this paper is to provide a review of the literature and to present the most important information on the current state of knowledge on mechanisms and the clinical significance of restenosis and in-stent restenosis in patients with DM, especially in association with the endovascular treatment of PAD. The role of such processes as inflammation, neointimal hyperplasia and neoatherosclerosis, allergy, resistance to antimitotic drugs used for coating stents and balloons, genetic factors, and technical and mechanical factors are discussed. The information on restenosis collected in this publication may be helpful in planning further research in this field, which may contribute to the formulation of more and more precise recommendations for the clinical practice.

Gut microbiota, key to unlocking the door of diabetic kidney disease

This review discusses the influence of gut microbiota dysbiosis on diabetic kidney disease through metabolite profile changes and immune and inflammatory mechanisms. We also elaborate on the mechanism of dysbiosis in the onset and development of other kidney diseases.

This review presents scientific evidence on the pathophysiologic links between gut microbiota and diabetic kidney disease (DKD), highlighting the influence of gut microbiota dysbiosis on DKD through metabolite profile changes and immunologic mechanisms.