LRG1 Human

What is the molecular structure of human LRG1?

LRG1 is a member of the highly conserved protein family containing leucine-rich-repeat (LRR) domains. The crystal structure reveals that LRG1 has a horseshoe-like solenoid structure with four N-glycosylation sites . The protein has a molecular weight of approximately 50,000 Da and contains multiple leucine-rich repeats that facilitate protein-protein interactions . These structural features are critical for understanding LRG1's binding properties and interactions with various biomolecules.

Where is LRG1 primarily expressed in humans?

While LRG1 mRNA has been detected in various human tissues, protein expression demonstrates tissue specificity. LRG1 is predominantly expressed in human adipose tissue compared to liver . Within adipose tissue, LRG1 is primarily produced by adipocytes rather than stromal vascular fractions (SVFs) . Additionally, LRG1 can be synthesized in primary human neutrophils during neutrophilic granulocyte differentiation and subsequently released extracellularly . Hepatocytes are also recognized as primary producers of circulating LRG1 .

What are normal concentration ranges of LRG1 in human samples?

In normal human plasma, LRG1 has a concentration range of 21-50 μg/mL . This baseline concentration serves as an important reference point for researchers investigating LRG1 in pathological conditions. Significant deviations from this range often correlate with various disease states, making LRG1 a potential biomarker for several conditions.

How does LRG1 function in metabolic disorders?

LRG1 has been identified as an obesity-associated adipokine that exacerbates high fat diet-induced hepatosteatosis and insulin resistance . Serum levels of LRG1 are markedly elevated in obese humans compared with lean individuals, and LRG1 mRNA levels positively correlate with body mass index (BMI) in human subcutaneous white adipose tissue . Mechanistically, LRG1 binds with high selectivity to the liver and promotes hepatosteatosis by increasing de novo lipogenesis and suppressing fatty acid β-oxidation . It also inhibits hepatic insulin signaling by downregulating insulin receptor substrates 1 and 2, contributing to insulin resistance .

What is the role of LRG1 in vascular biology and angiogenesis?

LRG1 has been identified as an important factor involved in pathogenic angiogenesis . It can promote both angiogenic and neurotrophic processes under hyperglycemic conditions by interacting with LPHN2 . Interestingly, LRG1 also demonstrates anti-inflammatory effects on endothelial cells. It inhibits TNF-α-induced activation of NF-κB signaling, expression of VCAM-1 and ICAM-1, and monocyte capture, firm adhesion, and transendothelial migration . This dual functionality makes LRG1 a complex target in vascular research.

What are validated methods for purifying and producing recombinant human LRG1?

Researchers have successfully developed protocols for recombinant human LRG1 (rhLRG1) production. One validated approach involves transfecting LRG1 plasmid into HEK293F cells using Lipofectamine 3000, followed by selection with G418 to establish a stable LRG1-overexpressing cell line . The conditioned medium can be concentrated using Amicon Ultra-15 Centrifugal Units, and rhLRG1 can be purified using Ni Sepharose beads . After elution, buffer exchange into phosphate-buffered saline (PBS) is performed using Amicon Ultra-15 Centrifugal Units, and protein concentration is determined by Bradford protein assay .

How can researchers effectively study LRG1 glycosylation patterns?

Studying LRG1 glycosylation is critical as the glycan composition significantly impacts its function. Research has shown that deglycosylation of LRG1, particularly the removal of glycans on N325, is critical for high-affinity binding of LRG1 to LPHN2 . This modification promotes LRG1/LPHN2-mediated angiogenic and neurotrophic processes in mouse tissue explants, even under normal glucose conditions . Researchers can study these patterns using techniques such as mass spectrometry, lectin binding assays, and site-directed mutagenesis of glycosylation sites followed by functional assays.

What cellular models are appropriate for studying LRG1 function?

Several cellular models have been validated for LRG1 research. For endothelial studies, human umbilical vein endothelial cells (HUVECs) and human aortic endothelial cells (HAECs) have been effectively used to investigate LRG1's role in endothelial activation . These cells can be cultured in Endothelial Cell Growth Basal Medium-2 (EBM-2) supplemented with appropriate growth factors . For adipocyte-related studies, both brown adipocytes and 3T3-L1 white adipocytes have been used to study LRG1 expression during differentiation .

How does LRG1 interact with different signaling pathways?

LRG1 modulates various signaling cascades, primarily TGFβ signaling . It exerts its function on TNFR1 shedding via the ALK5-SMAD2 pathway and subsequent activation of ADAM10 . This mechanism has been established through inhibitor studies using compounds such as GI254023X (ADAM10 inhibitor), LDN193189 (ALK1 inhibitor), and SB431542 (ALK5 inhibitor) . LRG1 also inhibits NF-κB signaling in endothelial cells, suggesting an anti-inflammatory role in vascular biology .

What is the significance of LRG1 in inflammatory diseases?

LRG1 functions as an acute phase protein with levels elevated in patients with bacterial infections. Interestingly, during inflammatory responses, LRG1 levels do not correlate with C-reactive protein (CRP) levels, suggesting independent regulation . LRG1 has been found to be highly expressed in endothelial cells of stenotic but not normal arteries, and its concentrations in serum of patients with critical limb ischemia (CLI) are elevated compared to healthy controls . There is a positive correlation between LRG1 and soluble TNFR1 in CLI patients, and causality between LRG1 and TNFR1 shedding has been established in mouse models .

What therapeutic strategies targeting LRG1 are being developed?

Antibody blockade of LRG1 has shown promise as a therapeutic approach in multiple pathologies associated with aberrant vascularization and vascular destabilization . A humanized monoclonal antibody called Magacizumab has been developed with therapeutic potential . This antibody was derived from a mouse monoclonal antibody (15C4) that, due to its specificity and near-irreversible picomolar affinity, was humanized for potential clinical trials .

How might LRG1 modulation impact metabolic disorders?

LRG1 deficiency in mice greatly alleviates diet-induced hepatosteatosis, obesity, and insulin resistance . This suggests that inhibiting LRG1 might be a potential therapeutic strategy for obesity-related metabolic disorders. The specific mechanisms through which LRG1 promotes metabolic dysfunction—increasing de novo lipogenesis, suppressing fatty acid β-oxidation, and inhibiting hepatic insulin signaling—provide multiple potential intervention points for therapeutic development .

What is the potential of LRG1 as a biomarker in clinical applications?

Beyond its roles in cancer detection, elevated levels of LRG1 in cerebrospinal fluid are being studied as markers for the early diagnosis of Parkinson's disease and progressive supranuclear palsy . Additionally, serum LRG1 levels correlate with diabetic complications, making it a potential prognostic marker in diabetes management . The relationship between LRG1 and soluble TNFR1 in critical limb ischemia patients suggests potential applications in monitoring inflammatory vascular diseases .