Zahraei Ali, Guo George, Varnava Kyriakos G, Demarais Nicholas J, Donaldson Paul J, Grey Angus C
Department of Physiology in the School of Medical Sciences, Auckland, New Zealand.
Mass Spectrometry Hub, Auckland, New Zealand.
Front Physiol. 2022 May 31;13:901407. doi: 10.3389/fphys.2022.901407. eCollection 2022.
To spatially correlate the pattern of glucose uptake to glucose transporter distributions in cultured lenses and map glucose metabolism in different lens regions. bovine lenses were incubated in artificial aqueous humour containing normoglycaemic stable isotopically-labelled (SIL) glucose (5 mM) for 5 min-20 h. Following incubations, lenses were frozen for subsequent matrix-assisted laser desorption/ionisation (MALDI) imaging mass spectrometry (IMS) analysis using high resolution mass spectrometry. Manually dissected, SIL-incubated lenses were subjected to gas chromatography-mass spectrometry (GC-MS) to verify the identity of metabolites detected by MALDI-IMS. Normal, unincubated lenses were manually dissected into epithelium flat mounts and fibre cell fractions and then subjected to either gel-based proteomic analysis (Gel-LC/MS) to detect facilitative glucose transporters (GLUTs) by liquid chromatography tandem mass spectrometry (LC-MS/MS). Indirect immunofluorescence and confocal microscopy of axial lens sections from unincubated fixed lenses labelled with primary antibodies specific for GLUT 1 or GLUT 3 were utilised for protein localisation. SIL glucose uptake at 5 min was concentrated in the equatorial region of the lens. At later timepoints, glucose gradually distributed throughout the epithelium and the cortical lens fibres, and eventually the deeper lens nucleus. SIL glucose metabolites found in glycolysis, the sorbitol pathway, the pentose phosphate pathway, and UDP-glucose formation were mapped to specific lens regions, with distinct regional signal changes up to 20 h of incubation. Spatial proteomic analysis of the lens epithelium detected GLUT1 and GLUT3. GLUT3 was in higher abundance than GLUT1 throughout the epithelium, while GLUT1 was more abundant in lens fibre cells. Immunohistochemical mapping localised GLUT1 to epithelial and cortical fibre cell membranes. The major uptake site of glucose in the bovine lens has been mapped to the lens equator. SIL glucose is rapidly metabolised in epithelial and fibre cells to many metabolites, which are most abundant in the metabolically more active cortical fibre cells in comparison to central fibres, with low levels of metabolic activity observed in the nucleus.
为了在空间上关联培养晶状体中葡萄糖摄取模式与葡萄糖转运蛋白分布,并绘制不同晶状体区域的葡萄糖代谢图谱,将牛晶状体在含有正常血糖稳定同位素标记(SIL)葡萄糖(5 mM)的人工房水中孵育5分钟至20小时。孵育后,将晶状体冷冻,以便随后使用高分辨率质谱进行基质辅助激光解吸/电离(MALDI)成像质谱(IMS)分析。对经SIL孵育的手动解剖晶状体进行气相色谱-质谱(GC-MS)分析,以验证MALDI-IMS检测到的代谢物的身份。将正常未孵育的晶状体手动解剖为上皮平铺片和纤维细胞部分,然后进行基于凝胶的蛋白质组学分析(凝胶液相色谱/质谱),通过液相色谱串联质谱(LC-MS/MS)检测易化葡萄糖转运蛋白(GLUTs)。利用针对GLUT 1或GLUT 3的一抗标记的未孵育固定晶状体轴向切片的间接免疫荧光和共聚焦显微镜进行蛋白质定位。5分钟时SIL葡萄糖摄取集中在晶状体赤道区域。在随后的时间点,葡萄糖逐渐分布到整个上皮和皮质晶状体纤维,最终到达更深的晶状体核。在糖酵解、山梨醇途径、磷酸戊糖途径和UDP-葡萄糖形成中发现的SIL葡萄糖代谢物被映射到特定的晶状体区域,在长达20小时的孵育过程中具有明显的区域信号变化。晶状体上皮的空间蛋白质组学分析检测到GLUT1和GLUT3。在整个上皮中,GLUT3的丰度高于GLUT1,而GLUT1在晶状体纤维细胞中更丰富。免疫组织化学图谱将GLUT1定位在上皮和皮质纤维细胞膜上。牛晶状体中葡萄糖的主要摄取部位已被映射到晶状体赤道。SIL葡萄糖在上皮和纤维细胞中迅速代谢为许多代谢物,与中央纤维相比,这些代谢物在代谢活性更高的皮质纤维细胞中最为丰富,在晶状体核中观察到的代谢活性较低。