Genome-Wide Association Analysis of Protein-Coding Variants in IgA Nephropathy.

SIGNIFICANCE STATEMENT: Genome-wide association studies have identified nearly 20 IgA nephropathy susceptibility loci. However, most nonsynonymous coding variants, particularly ones that occur rarely or at a low frequency, have not been well investigated. The authors performed a chip-based association study of IgA nephropathy in 8529 patients with the disorder and 23,224 controls. They identified a rare variant in the gene encoding vascular endothelial growth factor A (VEGFA) that was significantly associated with a two-fold increased risk of IgA nephropathy, which was further confirmed by sequencing analysis. They also identified a novel common variant in PKD1L3 that was significantly associated with lower haptoglobin protein levels. This study, which was well-powered to detect low-frequency variants with moderate to large effect sizes, helps expand our understanding of the genetic basis of IgA nephropathy susceptibility. BACKGROUND: Genome-wide association studies have identified nearly 20 susceptibility loci for IgA nephropathy. However, most nonsynonymous coding variants, particularly those occurring rarely or at a low frequency, have not been well investigated. METHODS: We performed a three-stage exome chip-based association study of coding variants in 8529 patients with IgA nephropathy and 23,224 controls, all of Han Chinese ancestry. Sequencing analysis was conducted to investigate rare coding variants that were not covered by the exome chip. We used molecular dynamic simulation to characterize the effects of mutations of VEGFA on the protein's structure and function. We also explored the relationship between the identified variants and the risk of disease progression. RESULTS: We discovered a novel rare nonsynonymous risk variant in VEGFA (odds ratio, 1.97; 95% confidence interval [95% CI], 1.61 to 2.41; P = 3.61×10 -11 ). Further sequencing of VEGFA revealed twice as many carriers of other rare variants in 2148 cases compared with 2732 controls. We also identified a common nonsynonymous risk variant in PKD1L3 (odds ratio, 1.16; 95% CI, 1.11 to 1.21; P = 1.43×10 -11 ), which was associated with lower haptoglobin protein levels. The rare VEGFA mutation could cause a conformational change and increase the binding affinity of VEGFA to its receptors. Furthermore, this variant was associated with the increased risk of kidney disease progression in IgA nephropathy (hazard ratio, 2.99; 95% CI, 1.09 to 8.21; P = 0.03). CONCLUSIONS: Our study identified two novel risk variants for IgA nephropathy in VEGFA and PKD1L3 and helps expand our understanding of the genetic basis of IgA nephropathy susceptibility.

Cloning, Synthesis and Functional Characterization of a Novel α-Conotoxin Lt1.3.

α-Conotoxins (α-CTxs) are small peptides composed of 11 to 20 amino acid residues with two disulfide bridges. Most of them potently and selectively target nicotinic acetylcholine receptor (nAChR) subtypes, and a few were found to inhibit the GABAB receptor (GABABR)-coupled N-type calcium channels (Cav2.2). However, in all of α-CTxs targeting both receptors, the disulfide connectivity arrangement "C¹-C³, C²-C4" is present. In this work, a novel α4/7-CTx named Lt1.3 (GCCSHPACSGNNPYFC-NH2) was cloned from the venom ducts of Conus litteratus (C. litteratus) in the South China Sea. Lt1.3 was then chemically synthesized and two isomers with disulfide bridges "C¹-C³, C²-C4" and "C¹-C4, C²-C³" were found and functionally characterized. Electrophysiological experiments showed that Lt1.3 containing the common disulfide bridges "C¹-C³, C²-C4" potently and selectively inhibited α3ß2 nAChRs and not GABABR-coupled Cav2.2. Surprisingly, but the isomer with the disulfide bridges "C¹-C4, C²-C³" showed exactly the opposite inhibitory activity, inhibiting only GABABR-coupled Cav2.2 and not α3ß2 nAChRs. These findings expand the knowledge of the targets and selectivity of α-CTxs and provide a new structural motif to inhibit the GABABR-coupled Cav2.2.

Systematic Microbiome Dysbiosis Is Associated with IgA Nephropathy.

IgA nephropathy (IgAN) is reportedly associated with microbial dysbiosis. However, the microbiome dysregulation of IgAN patients across multiple niches remains unclear. To gain a systematic understanding of microbial dysbiosis, we conducted large-scale 16S rRNA gene sequencing in IgAN patients and healthy volunteers across 1,732 oral, pharynx, gut, and urine samples. We observed a niche-specific increase of several opportunistic pathogens, including Bergeyella and Capnocytophaga in the oral and pharynx, whereas some beneficial commensals decreased in IgAN patients. Similar alterations were also observed in the early versus advanced stage of chronic kidney disease (CKD) progression. Moreover, Bergeyella, Capnocytophaga, and Comamonas in the oral and pharynx were positively associated with creatinine and urea, indicating renal lesions. Random forest classifiers were developed by using the microbial abundance to predict IgAN, achieving an optimal accuracy of 0.879 in the discovery phase and 0.780 in the validation phase. IMPORTANCE This study provides microbial profiles of IgAN across multiple niches and underlines the potential of these biomarkers as promising, noninvasive tools with which to differentiate IgAN patients for clinical applications.

Matrine Promotes Human Myeloid Leukemia Cells Apoptosis Through Warburg Effect Mediated by Hexokinase 2.

Matrine, an alkaloid compound isolated from the medicinal plant Sophora flavescens, inhibits many types of cancer proliferation. However, the precise mechanism of the matrine antihuman chronic myeloid leukemia remains unclear. In this study, we showed that matrine significantly inhibited the cell proliferation and induced apoptosis by regulating Warburg effect through controlling hexokinases 2 (HK2) expression in myeloid leukemia cells. Interestingly, matrine inhibited the expression of HK2 mediated by reduction in c-Myc binding to HK2 gene intron and led to downregulation of HK2, which upregulated proapoptotic protein Bad and then induced apoptosis. We further demonstrated that matrine could synergize with lonidamine, an inhibitor of HK2, for the treatment of myeloid leukemia, both in vitro and in vivo. Taken together, our findings reveal that matrine could promote human myeloid leukemia cells apoptosis via regulating Warburg effect by controlling HK2.

Targeting of N-Type Calcium Channels via GABAB-Receptor Activation by α-Conotoxin Vc1.1 Variants Displaying Improved Analgesic Activity.

α-Conotoxins exhibiting analgesic activity, such as Vc1.1, have been shown to inhibit α9α10 nicotinic acetylcholine receptors (nAChRs) and GABAB-receptor (GABABR) coupled N-type (CaV2.2) calcium channels. Here, we report two Vc1.1 variants, Vc1.1[N9R] and benzoyl-Vc1.1[N9R], that selectively inhibit CaV2.2 channels via GABABR activation but exhibit reduced inhibitory activity at α9α10 and other neuronal nAChR subtypes compared with Vc1.1. Surprisingly, the analgesic activity of Vc1.1[N9R] and benzoyl-Vc1.1[N9R] was more potent than that of Vc1.1 when tested in partial sciatic nerve ligation injury and chronic constriction injury models. Vc1.1[N9R] and benzoyl-Vc1.1[N9R] exhibited either similar or tenfold higher activity of GABABR-mediated CaV2.2 inhibition but no activity at CaV2.2 alone; however, the mechanism of increased analgesic activity is unknown. The effects on analgesic activity and α9α10 nAChR of other Vc1.1 variations at position 9 and the N-terminus were also determined. Our findings provide new insights for designing potent inhibitors for GABABR-coupled N-type (CaV2.2) calcium channels.