Abstract / Summary
Nogo (RTN4) proteins and their receptors have emerged as candidate mediators of metabolic regulation and vascular pathology relevant to type 2 diabetes (T2D). The primary objective of this PRISMA-guided systematic review was to evaluate the clinical and cohort evidence for RTN4/RTN4R as potential biomarkers of T2D progression and vascular complications. A secondary objective was to synthesize preclinical mechanistic evidence on the effects of Nogo axis modulation on pathways relevant to the pathogenesis of T2D. We performed a PRISMA-guided systematic review. The protocol was not prospectively registered in PROSPERO. To ensure reproducibility, we provide complete search keywords, the screening log and the full-text exclusion table. PubMed/MEDLINE, EMBASE and Web of Science were searched for studies published 2000-2025; full search keywords are provided in the main text. The search strategy combined and free-text terms with Boolean operators. We included original preclinical and clinical studies, cohort/proteomic analyses, meta-analyses, and mechanistic papers reporting expression, function, signaling, or clinical associations of Nogo proteins/receptors in metabolic or vascular outcomes. Exclusion criteria: non-English articles, unclear methods, studies outside 2000-2025, and studies lacking primary data. Two reviewers independently screened records; conflicts were resolved by consensus. Study quality was appraised using established tools (SYRCLE for animal studies, Newcastle-Ottawa Scale for cohort/case-control studies). Preclinical evidence supports tissue-specific roles for RTN4 isoforms and receptors in the regulation of insulin secretion, proGCG → GLP-1 processing, ER homeostasis, and vascular permeability through the Src/PI3K/Akt and RhoA/ROCK axes. Cohort and proteomic analyses report associations between RTN4/RTN4R or serum NogoB and faster progression of T2D or vascular complications, but genetic assessment of causality (Mendelian randomization) has so far provided limited support in available data sets. Findings are heterogeneous with respect to directionality and tissue localization. RTN4 signaling exhibits tissue-specific mechanisms relevant to glucose regulation and vascular biology and warrants further translational study. However, heterogeneity across studies and limited genetic support for causality indicate that isoform-specific quantitative validation, longitudinal cohorts and integrated genetic-functional analyses are required before RTN4/RTN4R can be considered as clinical biomarkers.
Primary Source
International journal of molecular sciences
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