Netrin-4 promotes pancreatic β-cell proliferation and insulin secretion in obesity by regulating translationally controlled tumor protein 1

BACKGROUNDNetrin-4 (NTN4) is a secreted laminin-like protein implicated in angiogenesis and tissue morphogenesis, yet its role in obesity-induced β-cell failure remains undefined.Chronic glucolipotoxicity progressively depletes β-cell mass by inducing apoptosis and impairing insulin secretion.We hypothesized that NTN4 preserves β-cell survival and function through interaction with the antiapoptotic protein translationally controlled tumor protein 1 (TPT1).AIM To determine whether NTN4 protects against obesity-induced β-cell dysfunction via TPT1.METHODS Islets from ob/ob, high-fat diet (HFD)-fed C57BL/6J mice, and palmitic acid and oleic acid mixture-treated MIN6 cells were used to assess NTN4 expression.Ntn4 wholebody knockout (Ntn4 -/-) mice (C57BL/6J, CRISPR/Cas9) received a normal chow diet (NCD) or an HFD for 20 weeks, after which the NTN4-loss phenotype, proliferation, apoptosis, and secretion were evaluated.TPT1 was identified as an NTN4 interactor by immunoprecipitation mass spectrometry, HDOCK docking, molecular dynamics, and endogenous co-immunoprecipitation. Epistasis (rescue): Eight-week-old mice received tail-vein AAV8-mIP2-NC-WPRE, AAV8-mIP2-Ntn4-WPRE with or without AAV8-mIP2-miR-E-shTpt1-WPRE, were fed an HFD for 20 weeks to assess metabolic indices, insulin indices, and proliferation/apoptosis markers. RESULTS / 45Obesity-related lipotoxic conditions reduce pancreatic NTN4 levels.Compared with wild-type mice, Ntn4 -/-mice fed an NCD exhibited no obvious phenotypic differences, but after they were fed an HFD, they gained more weight, exhibited hyperglycemia, reduced fasting insulin levels, and exhibited impaired glucose/insulin tolerance and glucose-stimulated insulin secretion.Ntn4 deficiency suppressed islet proliferation and insulin secretion while promoting apoptosis, effects exacerbated by lipotoxicity.NTN4 interacts with TPT1 and positively regulates its expression under lipotoxic stress.Mechanistically, HFD-AAV8-Ntn4 improved metabolic parameters and β-cell function, whereas concurrent Tpt1 knockdown largely reversed these protective effects, indicating that NTN4 may act via TPT1 to preserve islet function. CONCLUSIONNTN4 may protect pancreatic β-cells against obesity through TPT1, identifying the NTN4-TPT1 axis as a potential therapeutic target for diabetes.