Microthrombotic Renal Vascular Lesions Are Associated to Increased Renal Inflammatory Infiltration in Murine Lupus Nephritis

Risk Factors and Clinical Outcomes of Renal Thrombotic Microangiopathy in Children with Lupus Nephritis in Terms of Pathological and Clinical Features

BACKGROUND

Thrombotic microangiopathy (TMA) is an important risk factor for the prognosis of lupus nephritis (LN). Patients with LN complicated with TMA tend to be critically ill with high mortality and poor prognosis. In the present study, we retrospectively analyzed the clinical manifestations, laboratory results, renal pathological manifestations, and prognosis of children with LN-TMA and analyzed the risk factors for end-stage renal disease (ESRD) in children with LN-TMA.

METHODS

Seventy-four patients with LN and renal TMA (rTMA) were selected and compared to 128 LN controls without TMA (1:2 ratio) matched according to demographics, pathological type and treatments.

RESULTS

The mean values of systolic blood pressure, diastolic blood pressure (DBP), lactate dehydrogenase (LDH), blood urea nitrogen (BUN), urinary protein quantitation (PRO), urine red blood cells, N-acetyl-β-D-glucosidase (NAG), retinol-binding protein, systemic lupus erythematosus disease activity score (SLEDAI), and activity index (AI) scores in the TMA group were all higher than those in the non-TMA group (p < 0.05 and p < 0.01). The mean values of complement C3, hemoglobin, platelets, estimated glomerular filtration rate, and chronic index (CI) score in the TMA group were all lower than those in the non-TMA group (p < 0.05 and p < 0.01). The number of cases of glomerular crescent, fibrous crescent, endocapillary proliferation, tubular atrophy, interstitial fibrosis, C3 and C1q deposition in the TMA group was higher than that in the non-TMA group (p < 0.05 and p < 0.01). The 3-year and 5-year renal survival rates in the TMA group (88.93% vs. 97.00%, p < 0.05) and TMA group (61.41% vs. 82.31%, p < 0.05) were significantly lower than those in the non-TMA group. Multivariate Cox regression analysis showed that serum creatinine before treatment (≥110 μmol/L), TMA and interstitial fibrosis were independent risk factors for the development of ESRD in LN children.

CONCLUSION

The general condition of children with TMA is critical, and the prognosis is poor. Early detection, early treatment and the development of new treatments are key to improving LN-TMA outcomes in children.

Renal Tissue-Derived Exosomal miRNA-34a in Diabetic Nephropathy Induces Renal Tubular Cell Fibrosis by Promoting the Polarization of M1 Macrophages

Background

Diabetic nephropathy (DN) is the leading cause of chronic kidney disease, and the activation and infiltration of phagocytes are critical steps of DN. This study aimed to explore the mechanism of exosomes in macrophages and diabetes nephropathy and the role of miRNA-34a, which might provide a new path for treating DN.

Materials and Methods

The DN model was established, and the success of the model establishment was confirmed by detecting general indicators, HE staining, and immunohistochemistry. Electron microscopy and NanoSight Tracking Analysis (NTA) were used to see the morphology and size of exosomes. MiRNA-34a inhibitor, miRNA-34a mimics, pc-PPARGC1A, and controls were transfected in macrophages with or without kidney exosomal. A dual-luciferase reporter gene experiment verifies the targeting relationship between miRNA-34a and PPARGC1A. After exosomal culture, macrophages are co-cultured with normal renal tubular cells to detect renal tubular cell fibrosis. Q-PCR and western blot were undertaken to detect related RNA and proteins.

Results

An animal model of diabetic nephropathy was successfully constructed. Macrophages could phagocytose exosomes. After ingesting model exosomes, M1 macrophages were activated, while M2 macrophages were weakened, indicating the model mice's kidney exosomes caused the polarization. MiRNA-34a inhibitor increased PPARGC1A expression. MiRNA-34a expressed higher in diabetic nephropathy Model-Exo. MiRNA-34a negatively regulated PPARGC1A. PPARGC1A rescued macrophage polarization and renal tubular cell fibrosis.

Conclusion

Exosomal miRNA-34a of tubular epithelial cells promoted M1 macrophage activation in diabetic nephropathy via negatively regulating PPARGC1A expression, which may provide a new direction for further exploration of DN treatment.

Macrophages in Lupus Nephritis: Exploring a potential new therapeutic avenue

Lupus nephritis (LN) is a serious complication of systemic lupus erythematosus (SLE) that occurs in about half of patients. LN is characterized by glomerular deposition of immune complexes, leading to subendothelial, mesangial and subepithelial electron dense deposits, triggering immune cell infiltration and glomerular as well as tubulointerstitial injury. Monocytes and macrophages are abundantly present in inflammatory lesions, both in glomeruli and the tubulointerstitium. Here we discuss how monocytes and macrophages are involved in this process and how monocytes and macrophages may represent specific therapeutic targets to control LN.

The role of the complement system in kidney glomerular capillary thrombosis

The complement system is part of the innate immune system. The crucial step in activating the complement system is the generation and regulation of C3 convertase complexes, which are needed to generate opsonins that promote phagocytosis, to generate C3a that regulates inflammation, and to initiate the lytic terminal pathway through the generation and activity of C5 convertases. A growing body of evidence has highlighted the interplay between the complement system, coagulation system, platelets, neutrophils, and endothelial cells. The kidneys are highly susceptible to complement-mediated injury in several genetic, infectious, and autoimmune diseases. Atypical hemolytic uremic syndrome (aHUS) and lupus nephritis (LN) are both characterized by thrombosis in the glomerular capillaries of the kidneys. In aHUS, congenital or acquired defects in complement regulators may trigger platelet aggregation and activation, resulting in the formation of platelet-rich thrombi in the kidneys. Because glomerular vasculopathy is usually noted with immunoglobulin and complement accumulation in LN, complement-mediated activation of tissue factors could partly explain the autoimmune mechanism of thrombosis. Thus, kidney glomerular capillary thrombosis is mediated by complement dysregulation and may also be associated with complement overactivation. Further investigation is required to clarify the interaction between these vascular components and develop specific therapeutic approaches.

Microarray-based analysis of renal complement components reveals a therapeutic target for lupus nephritis

Background

Screening abnormal pathways and complement components in the kidneys of patients with lupus nephritis (LN) and NZB/W mice may help to identify complement-related therapeutic targets for LN.

Methods

KEGG and GO enrichment assays were used to analyze kidney microarray data of LN patients and NZB/W mice. Immunohistochemistry and immunofluorescence assays were used to measure renal expression of complement-related proteins and TGFβ1. Cytokines were measured using RT-qPCR and ELISA.

Results

We screened the renal pathogenic pathways present in LN patients and NZB/W mice and selected the complement activation pathway for further study. The results indicated greater renal expression of C1qa, C1qb, C3, C3aR1, and C5aR1 at the mRNA and protein levels. C3 appeared to be a key factor in LN and the renal signaling downstream of C1 was inhibited. There were significant correlations between the expression of TGFβ1 and C3. Analysis of primary cell cultures indicated that TGFβ1 promoted the expression of C3 and that a TGFβ1 antagonist decreased the levels of C3 and C3aR. TGFβ1 inhibition significantly inhibited the deposition of complement-related factors in the kidneys of NZB/W mice.

Conclusions

At the onset of LN, there are significant increases in the renal levels of C3 and other complement pathway-related factors in patients with LN and NZB/W mice. C3 may lead to albuminuria and participate in the pathogenesis of LN. TGFβ1 promotes C3 synthesis, and TGFβ1 inhibition may block the progression of LN by inhibiting the synthesis of C3 and other complement components.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13075-021-02605-9.

Arachidonic Acid Metabolism and Kidney Inflammation

As a major component of cell membrane lipids, Arachidonic acid (AA), being a major component of the cell membrane lipid content, is mainly metabolized by three kinds of enzymes: cyclooxygenase (COX), lipoxygenase (LOX), and cytochrome P450 (CYP450) enzymes. Based on these three metabolic pathways, AA could be converted into various metabolites that trigger different inflammatory responses. In the kidney, prostaglandins (PG), thromboxane (Tx), leukotrienes (LTs) and hydroxyeicosatetraenoic acids (HETEs) are the major metabolites generated from AA. An increased level of prostaglandins (PGs), TxA₂ and leukotriene B4 (LTB₄) results in inflammatory damage to the kidney. Moreover, the LTB₄-leukotriene B4 receptor 1 (BLT1) axis participates in the acute kidney injury via mediating the recruitment of renal neutrophils. In addition, AA can regulate renal ion transport through 19-hydroxystilbenetetraenoic acid (19-HETE) and 20-HETE, both of which are produced by cytochrome P450 monooxygenase. Epoxyeicosatrienoic acids (EETs) generated by the CYP450 enzyme also plays a paramount role in the kidney damage during the inflammation process. For example, 14 and 15-EET mitigated ischemia/reperfusion-caused renal tubular epithelial cell damage. Many drug candidates that target the AA metabolism pathways are being developed to treat kidney inflammation. These observations support an extraordinary interest in a wide range of studies on drug interventions aiming to control AA metabolism and kidney inflammation.