LGR6 ameliorates diabetic adipose dysfunction via inhibiting ferroptosis

Technical Summary: LGR6 Ameliorates Diabetic Adipose Dysfunction via Inhibiting Ferroptosis

Problem Statement
Type 2 diabetes mellitus (T2DM) is characterized by chronic hyperglycemia and systemic metabolic dysregulation, with adipose tissue (AT) dysfunction serving as a cornerstone of disease progression. While the roles of glucotoxicity and lipotoxicity in cellular stress are recognized, the specific molecular mechanisms driving adipocyte death and dysfunction under high-glucose conditions remain incompletely understood. Specifically, the role of ferroptosis—an iron-dependent form of regulated cell death driven by lipid reactive oxygen species (ROS)—in diabetic adipose tissue has not been fully elucidated. Furthermore, the physiological function of Leucine-rich repeat-containing G-protein-coupled receptor 6 (LGR6), a known enhancer of the Wnt/β-catenin signaling pathway, within adipose tissue and its potential link to ferroptosis in the context of T2DM is unknown.

Methodology
This study employed a multi-level experimental design integrating human clinical samples, animal models, and in vitro cell systems:

• Human Transcriptomics and Histology: Comparative transcriptomic analysis was performed on visceral adipose tissue from 10 T2DM patients and 10 healthy controls. This was supplemented by histological analysis (H&E, immunofluorescence, immunohistochemistry) to assess adipocyte morphology, inflammation, and LGR6 protein expression.
• Animal Models: A streptozotocin (STZ)-induced diabetic mouse model (C57BL/6J) was utilized. To modulate LGR6 expression in vivo, adeno-associated virus serotype 9 (AAV9) for overexpression (AAV9-LGR6) and adenovirus for knockdown (Ad-shLGR6) were locally injected into epididymal fat pads.
• In Vitro Models: Adipose-derived stem cells (ADSCs) were isolated from human and mouse tissues and cultured under high-glucose (25 mmol/L) conditions to mimic the diabetic microenvironment.
• Molecular and Functional Assays: Techniques included qRT-PCR, Western blotting, and transcriptomic sequencing (RNA-seq) to analyze gene expression. Ferroptosis markers were assessed via intracellular iron assays, ROS detection (DHE staining), and lipid accumulation (BODIPY staining). Bioinformatics tools (GO, KEGG, GSEA, PPI networks) were used to interpret transcriptomic data.

Key Contributions and Results

1. LGR6 Downregulation in Diabetes: Transcriptomic analysis of human and mouse adipose tissues revealed a significant downregulation of LGR6 in diabetic groups compared to controls. This downregulation correlated with the activation of inflammatory pathways (e.g., JAK-STAT, TNF signaling) and the suppression of the Wnt signaling pathway.
2. Correlation with Adipose Dysfunction: In diabetic patients and STZ-induced mice, reduced LGR6 expression was associated with marked adipocyte hypertrophy, impaired adipogenic capacity (reduced expression of PPARγ, CEBPA, FABP4), and elevated inflammation. In vitro, high-glucose conditions suppressed LGR6 expression in ADSCs, leading to impaired differentiation and increased ferroptosis markers.
3. Ferroptosis Activation: The study identified ferroptosis as a significantly enriched pathway in diabetic adipose tissue. Diabetic conditions led to increased intracellular iron, lipid ROS accumulation, and upregulation of ferroptosis-related genes (TFR1, p53) while downregulating protective markers (GPX4, FTH1).
4. Mechanistic Role of LGR6:
   • Loss-of-Function: Knockdown of LGR6 in diabetic mice exacerbated adipocyte hypertrophy, inflammation, and ferroptosis (increased iron and ROS).
   • Gain-of-Function: Overexpression of LGR6 in diabetic mice and high-glucose-treated ADSCs reversed these effects. It restored adipogenic markers (PPARγ), suppressed ferroptosis (reduced TFR1, p53, and ROS), and maintained cellular homeostasis.
   • Signaling Axis: The study proposes that LGR6 maintains adipogenic capacity and inhibits ferroptosis via the Wnt/β-catenin/p53 signaling axis. Specifically, LGR6 appears to suppress p53 levels (which otherwise promote ferroptosis by repressing SLC7A11 and depleting glutathione), thereby raising the threshold for oxidative damage.

Significance and Claims
The authors claim to have identified a novel LGR6 signaling pathway that critically regulates ferroptosis and adipogenic disorders in diabetic adipose tissue. The study provides the first evidence linking LGR6 signaling to the suppression of ferroptosis in adipocytes.

The paper posits that the downregulation of LGR6 in diabetes triggers a p53-associated ferroptotic cascade characterized by iron accumulation and lipid peroxidation, which drives adipose tissue inflammation and dysfunction. Consequently, the authors suggest that strategies aimed at potentiating the LGR6-Wnt signaling axis could offer a therapeutic strategy for diabetic adiposopathy by simultaneously blocking pathological ferroptosis and preserving adipocyte adipogenic capacity.

The authors acknowledge limitations, including the use of an STZ-induced model which may not fully recapitulate the insulin-resistant state of early T2DM, the relatively small human sample size, and the need for further validation of the precise molecular intermediates between LGR6 and p53. They conclude that while their findings are promising, the therapeutic potential of targeting LGR6 requires further investigation in more physiologically relevant models.