Global knockout of VEGFB improves lipoprotein lipase activity leading to an improved lipid profile during diabetes
Diabetes affects over half a billion people worldwide, with cardiovascular disease Q7 being its leading cause of death, either occurring secondary to atherosclerosis or due to an intrinsic defect in heart muscle (diabetic cardiomyopathy, DbCM). One instigator for DbCM is impaired cardiac metabolism characterized by excessive fatty acid (FA) delivery and utilization by the heart, causing oxidative stress and toxic lipid accumulation. Inhibition of vascular endothelial growth factor B (VEGFB) has been shown to counter these factors associated with abnormal cardiac metabolism by inducing metabolic flexibility and preventing cardiac lipid accumulation in Type 2 diabetes. However, its impact on lipoprotein lipase (LPL) and the sources of FA for cardiac use in Type 1 diabetes is unknown. Global Vegfb knockout (VegfbKO) in rats caused limited phenotype and cardiac transcriptome changes under normal conditions but notably reduced cardiac LPL activity, probably by impeding LPL translocation from cardiomyocyte to the coronary vasculature. Under streptozotocin (STZ)-induced diabetes, VegfbKO rats exhibited increased cardiac LPL activity, protecting animals from dyslipidemia, decreased plasma saturated FA, and provided a safer cardiac FA source, LPL-derived FA. Knockout of Vegfb also protected animals from DbCM by inhibiting excess FA oxidation, preserving angiogenesis and alleviating cell death in the heart. Inhibiting VEGFB may offer a promising therapeutic approach to address the current lack of mechanism-based treatments for DbCM. Overall design: VEGFB knockout (KO) rats were created on a Sprague Dawley background rats by inserting a beta-glucosidase gene to disrupt the VEGFB gene using zinc-finger nucleases. Wildtype and global VEGFB KO rats were housed until 7 weeks of age. Diabetes was induced by intravenous administration of streptozotocin (55 mg/kg) to kill insulin production beta cell. Given the sex differences in the susceptibility to STZ diabetes, only male rats were used for this study. All animals injected with STZ developed hyperglycemia and hypoinsulinemia within 24 hours. Animals were monitored for 4 days. On day 4 of diabetes, cardiac tissue was collected from diabetic rats and their littermate-matched controls. So we have four experimental groups: wildtype control (WTC), wildtype diabetic (WTD), VEGFB KO control (KOC), and VEGFB KO diabetic (KOD)(n = 5 for each group).  Total RNA was extracted from frozen ventricular tissue using TRIzol reagent according to the manufacturer's protocol. The concentration and purity of the RNA samples were checked by Qubit fluorometer. And the RNA integrity of the RNA samples was checked by Bioanalyzer. Then, we sent our qualified RNA sample to Sequencing Core Facility for library preparation and sequencing. The sequencing library was prepared using NEBNext Ultra II Directional RNA library Prep Kit and sequenced using Illumina Nextseq 500 platform to generate paired-end reads.