Integrin beta3 Deficiency Results in Hypertriglyceridemia Via Disrupting LPL (Lipoprotein Lipase) Secretion.

OBJECTIVE: Integrin beta3 is implicated in numerous biological processes such as its relevance to blood triglyceride, yet whether beta3 deficiency affects this metabolic process remains unknown. Approach and Results: We showed that the Chinese patients with beta3-deficient Glanzmann thrombasthenia had a 2-fold higher serum triglyceride level together with a lower serum LPL (lipoprotein lipase) level than those with an alphaIIb deficiency or healthy subjects. The beta3 knockout mice recapitulated these phenotypic features. The elevated plasma triglyceride level was due to impaired LPL-mediated triglyceride clearance caused by a disrupted LPL secretion. Further analysis revealed that beta3 directly bound LPL via a juxtamembrane TIH(720)(-722) motif in its cytoplasmic domain and functioned as an adaptor protein by interacting with LPL and PKD (protein kinase D) to form the PKD/beta3/LPL complex that is required for beta3-mediated LPL secretion. Furthermore, the impaired triglyceride clearance in beta3 knockout mice could be corrected by adeno-associated virus serotype 9 (AAV9)-mediated delivery of wild-type but not TIH(720-)(722)-mutated beta3 genes. CONCLUSIONS: This study reveals a hypertriglyceridemia in both beta3-deficient Chinese patients and mice and provides novel insights into the molecular mechanisms of the significant roles of beta3 in LPL secretion and triglyceride metabolism, drawing attention to the metabolic consequences in patients with beta3-deficient Glanzmann thrombasthenia.