Association of Genetic Variants for Plasma LRG1 With Rapid Decline in Kidney Function in Patients With Type 2 Diabetes

LRG1 Contributes to the Pathogenesis of Multiple Kidney Diseases: A Comprehensive Review

Background

The increasing prevalence of kidney diseases has become a significant public health issue, with a global prevalence exceeding 10%. In order to accurately identify biochemical changes and treatment outcomes associated with kidney diseases, novel methods targeting specific genes have been discovered. Among these genes, leucine-rich α-2 glycoprotein 1 (LRG1) has been identified to function as a multifunctional pathogenic signaling molecule in multiple diseases, including kidney diseases. This study aims to provide a comprehensive overview of the current evidence regarding the roles of LRG1 in different types of kidney diseases.

Summary

Based on a comprehensive review, it was found that LRG1 was upregulated in the urine, serum, or renal tissues of patients or experimental animal models with multiple kidney diseases, such as diabetic nephropathy, kidney injury, IgA nephropathy, chronic kidney diseases, clear cell renal cell carcinoma, end-stage renal disease, canine leishmaniosis-induced kidney disease, kidney fibrosis, and aristolochic acid nephropathy. Mechanistically, the role of LRG1 in kidney diseases is believed to be detrimental, potentially through its regulation of various genes and signaling cascades, i.e., fibronectin 1, GPR56, vascular endothelial growth factor (VEGF), VEGFR-2, death receptor 5, GDF15, HIF-1α, SPP1, activin receptor-like kinase 1-Smad1/5/8, NLRP3-IL-1b, and transforming growth factor β pathway.

Key Messages

Further research is needed to fully comprehend the molecular mechanisms by which LRG1 contributes to the pathogenesis and pathophysiology of kidney diseases. It is anticipated that targeted treatments focusing on LRG1 will be utilized in clinical trials and implemented in clinical practice in the future.

The disruptive role of LRG1 on the vasculature and perivascular microenvironment

The establishment of new blood vessels, and their subsequent stabilization, is a critical process that facilitates tissue growth and organ development. Once established, vessels need to diversify to meet the specific needs of the local tissue and to maintain homeostasis. These processes are tightly regulated and fundamental to normal vessel and tissue function. The mechanisms that orchestrate angiogenesis and vessel maturation have been widely studied, with signaling crosstalk between endothelium and perivascular cells being identified as an essential component. In disease, however, new vessels develop abnormally, and existing vessels lose their specialization and function, which invariably contributes to disease progression. Despite considerable research into the vasculopathic mechanisms in disease, our knowledge remains incomplete. Accordingly, the identification of angiocrine and angiopathic molecules secreted by cells within the vascular microenvironment, and their effect on vessel behaviour, remains a major research objective. Over the last decade the secreted glycoprotein leucine-rich α-2 glycoprotein 1 (LRG1), has emerged as a significant vasculopathic molecule, stimulating defective angiogenesis, and destabilizing the existing vasculature mainly, but not uniquely, by altering both canonical and non-canonical TGF-β signaling in a highly cell and context dependent manner. Whilst LRG1 does not possess any overt homeostatic role in vessel development and maintenance, growing evidence provides a compelling case for LRG1 playing a pleiotropic role in disrupting the vasculature in many disease settings. Thus, LRG1 has now been reported to damage vessels in various disorders including cancer, diabetes, chronic kidney disease, ocular disease, and lung disease and the signaling processes that drive this dysfunction are being defined. Moreover, therapeutic targeting of LRG1 has been widely proposed to re-establish a quiescent endothelium and normalized vasculature. In this review, we consider the current status of our understanding of the role of LRG1 in vascular pathology, and its potential as a therapeutic target.

Variants within the LPL gene confer susceptility to diabetic kidney disease and rapid decline in kidney function in Chinese patients with type 2 diabetes

AIM

To examine the association between lipoprotein lipase (LPL) polymorphisms and susceptibility to diabetic kidney disease (DKD) and early renal function decline in Chinese patients with type 2 diabetes (T2D).

METHODS

The association of eight LPL single nucleotide polymorphisms (SNPs) with DKD was analysed in 2793 patients with T2D from the third China National Stroke Registry. DKD was defined as either an urine albumin-to-creatinine ratio (UACR) of 30 mg/g or higher at baseline and 3 months, or an estimated glomerular filtration rate (eGFR) of less than 60 mL/min/1.73 m2 at baseline and 3 months. Rapid decline in kidney function (RDKF) was defined as a reduction in the eGFR of 3 mL/min/1.73 m2 or greater per year. Logistic regression models were used to evaluate the association of LPL SNP and DKD with an additive model.

RESULTS

The SNPs rs285 C>T (OR = 1.40, P = .0154), rs328 C>G (OR = 2.24, P = .0104) and rs3208305 A>T (OR = 1.85, P = .0015) were identified to be significantly associated with DKD defined by eGFR. Among 1241 participants with follow-up data, 441 (35.5%) showed RDKF over a mean follow-up period of 1 year, and the rs285 C allele was associated with higher odds of RDKF (OR = 1.31, 95% CI 1.04-1.66; P = .025) after adjustment for multiple variables.

CONCLUSIONS

These results suggest that LPL-related SNPs are new candidate factors for conferring susceptibility to DKD and may promote rapid loss of renal function in Chinese patients with T2D.

Genetic Risk Score for Plasma Uric Acid Levels Is Associated With Early Rapid Kidney Function Decline in Type 2 Diabetes

CONTEXT

Observational studies have shown that elevated uric acid (UA) is associated with chronic kidney disease (CKD). However, whether the relationship is causal remains unclear.

OBJECTIVE

To determine the association of plasma UA and incident CKD and the causal relationship between plasma UA and rapid decline in kidney function (RDKF) in patients with type 2 diabetes (T2D).

METHODS

Multivariable Cox regression was conducted to evaluate the hazard ratio (HR) between plasma UA and incident CKD among 1300 normoalbuminuric patients in 2 T2D study cohorts (DN, n = 402; SMART2D, n = 898). A weighted genetic risk score (wGRS) was calculated based on 10 single nucleotide polymorphism (SNPs) identified in genome-wide association studies of UA in East Asians. Mendelian randomization (MR) analysis was performed among 1146 Chinese T2D patients without CKD (estimated glomerular filtration rate [eGFR] > 60 mL/min/1.73m2) at baseline (DN, 478; SMART2D, 668). The wGRS and individual SNPs were used as genetic instruments and RDKF was defined as eGFR decline of 5 mL/min/1.73m2/year or greater.

RESULTS

During mean follow-up of 5.2 and 5.4 years, 81 (9%) and 46 (11%) participants in SMART2D and DN developed CKD, respectively. A 1-SD increment in plasma UA conferred higher risk of incident CKD (DN, adjusted-HR = 1.40 [95% CI, 1.02-1.91], P = 0.036; SMART2D, adjusted-HR = 1.31 [95% CI, 1.04-1.64], P = 0.018). Higher wGRS was associated with increased odds for RDKF (meta-adjusted odds ratio = 1.12 [95% CI, 1.01-1.24], P = 0.030, Phet = 0.606).

CONCLUSION

Elevated plasma UA is an independent risk factor for incident CKD. Furthermore, plasma UA potentially has a causal role in early eGFR loss in T2D patients.

Research Progress on Leucine-Rich Alpha-2 Glycoprotein 1: A Review

Leucine-rich alpha⁃2 glycoprotein 1 (LRG1) is an important member of the leucine-rich repetitive sequence protein family. LRG1 was mainly involved in normal physiological activities of the nervous system, such as synapse formation, synapse growth, the development of nerve processes, neurotransmitter transfer and release, and cell adhesion molecules or ligand-binding proteins. Also, LRG1 affected the development of respiratory diseases, hematological diseases, endocrine diseases, tumor diseases, eye diseases, cardiovascular diseases, rheumatic immune diseases, infectious diseases, etc. LRG1 was a newly discovered important upstream signaling molecule of transforming growth factor⁃β (TGF⁃β) that affected various pathological processes through the TGF⁃β signaling pathway. However, research on LRG1 and its involvement in the occurrence and development of diseases was still in its infancy and the current studies were mainly focused on proteomic detection and basic animal experimental reports. We could reasonably predict that LRG1 might act as a new direction and strategy for the treatment of many diseases.

LRG1: an emerging player in disease pathogenesis

The secreted glycoprotein leucine-rich α-2 glycoprotein 1 (LRG1) was first described as a key player in pathogenic ocular neovascularization almost a decade ago. Since then, an increasing number of publications have reported the involvement of LRG1 in multiple human conditions including cancer, diabetes, cardiovascular disease, neurological disease, and inflammatory disorders. The purpose of this review is to provide, for the first time, a comprehensive overview of the LRG1 literature considering its role in health and disease. Although LRG1 is constitutively expressed by hepatocytes and neutrophils, Lrg1-/- mice show no overt phenotypic abnormality suggesting that LRG1 is essentially redundant in development and homeostasis. However, emerging data are challenging this view by suggesting a novel role for LRG1 in innate immunity and preservation of tissue integrity. While our understanding of beneficial LRG1 functions in physiology remains limited, a consistent body of evidence shows that, in response to various inflammatory stimuli, LRG1 expression is induced and directly contributes to disease pathogenesis. Its potential role as a biomarker for the diagnosis, prognosis and monitoring of multiple conditions is widely discussed while dissecting the mechanisms underlying LRG1 pathogenic functions. Emphasis is given to the role that LRG1 plays as a vasculopathic factor where it disrupts the cellular interactions normally required for the formation and maintenance of mature vessels, thereby indirectly contributing to the establishment of a highly hypoxic and immunosuppressive microenvironment. In addition, LRG1 has also been reported to affect other cell types (including epithelial, immune, mesenchymal and cancer cells) mostly by modulating the TGFβ signalling pathway in a context-dependent manner. Crucially, animal studies have shown that LRG1 inhibition, through gene deletion or a function-blocking antibody, is sufficient to attenuate disease progression. In view of this, and taking into consideration its role as an upstream modifier of TGFβ signalling, LRG1 is suggested as a potentially important therapeutic target. While further investigations are needed to fill gaps in our current understanding of LRG1 function, the studies reviewed here confirm LRG1 as a pleiotropic and pathogenic signalling molecule providing a strong rationale for its use in the clinic as a biomarker and therapeutic target.

Association of Plasma Leucine-Rich Alpha-2 Glycoprotein 1 (LRG1) with All-Cause and Cause-Specific Mortality in Individuals with Type 2 Diabetes

BACKGROUND

Leucine-rich alpha-2 glycoprotein 1 (LRG1) is a circulating protein in the transforming growth factor-beta superfamily. We sought to study whether LRG1 might predict risk for all-cause and cause-specific mortality in individuals with type 2 diabetes.

METHODS

2012 outpatients with type 2 diabetes were followed for a median of 7.2 years and 188 death events were identified. Association of LRG1 with risk for mortality was assessed by multivariable Cox regression models.

RESULTS

Participants with a higher concentration of LRG1 had an increased risk for all-cause mortality [HR (95% CI), 1.76 (1.03-3.01), 1.75 (1.03-2.98), and 4.37 (2.72-7.02) for quartiles 2, 3, and 4, respectively, compared to quartile 1]. The association remained significant after adjustment for known cardio-renal risk factors including estimated glomerular filtration rate and albuminuria [adjusted HR 2.76 (1.66-4.59), quartile 4 versus 1]. As a continuous variable, a 1-SD increment in LRG1 was associated with 1.34 (1.14-1.57)-fold adjusted risk for all-cause mortality. High plasma LRG1 was independently associated with mortality attributable to cardiovascular disease, infection, and renal diseases. Adding LRG1 into a clinical variable-based model improved discrimination (c statistics from 0.828 to 0.842, P = 0.006) and reclassification (net reclassification improvement 0.47, 95% CI 0.28-0.67) for prediction of 5-year all-cause mortality.

CONCLUSION

Plasma LRG1 predicts risk for all-cause mortality and mortality attributable to cardiovascular disease, infection, and renal disease independent of known cardio-renal risk factors. It may be a potential novel biomarker to improve risk stratification in individuals with type 2 diabetes.

Association of Genetic Variants for Plasma LRG1 With Rapid Decline in Kidney Function in Patients With Type 2 Diabetes

CONTEXT

Elevated levels of plasma leucine-rich α-2-glycoprotein 1 (LRG1), a component of transforming growth factor beta signaling, are associated with development and progression of chronic kidney disease in patients with type 2 diabetes (T2D). However, whether this relationship is causal is uncertain.

OBJECTIVES

To identify genetic variants associated with plasma LRG1 levels and determine whether genetically predicted plasma LRG1 contributes to a rapid decline in kidney function (RDKF) in patients with T2D.

DESIGN AND PARTICIPANTS

We performed a genome-wide association study of plasma LRG1 among 3694 T2D individuals [1881 (983 Chinese, 420 Malay, and 478 Indian) discovery from Singapore Study of Macro-angiopathy and Micro-vascular Reactivity in Type 2 Diabetes cohort and 1813 (Chinese) validation from Diabetic Nephropathy cohort]. One- sample Mendelian randomization analysis was performed among 1337 T2D Chinese participants with preserved glomerular filtration function [baseline estimated glomerular filtration rate (eGFR) ≥60 mL/min/1.73 m2)]. RDKF was defined as an eGFR decline of 3 mL/min/1.73 m2/year or greater.

RESULTS

We identified rs4806985 variant near LRG1 locus robustly associated with plasma LRG1 levels (meta P = 6.66 × 10-16). Among 1337 participants, 344 (26%) developed RDKF, and the rs4806985 variant was associated with higher odds of RDKF (meta odds ratio = 1.23, P = 0.030 adjusted for age and sex). Mendelian randomization analysis provided evidence for a potential causal effect of plasma LRG1 on kidney function decline in T2D (P < 0.05).

CONCLUSION

We demonstrate that genetically influenced plasma LRG1 increases the risk of RDKF in T2D patients, suggesting plasma LRG1 as a potential treatment target. However, further studies are warranted to elucidate underlying pathways to provide insight into diabetic kidney disease prevention.