Alpha-granule membrane mirrors the platelet plasma membrane and contains the glycoproteins Ib, IX, and V

Abstract

We have recently shown that several components from the platelet plasma membrane were also present at different rates in the alpha-granule membrane. This is the case for the glycoprotein (GP) IIb-IIIa (CD41), CD36, CD9, PECAM1, and Rap1b, while the GPIB-IX-V complex was considered to escape the rule. In this investigation, we studied the subcellular localization of GPIb, GPIX, and GPV in the resting platelets of normal subjects, patients with Bernard-Soulier syndrome, patients with Gray platelet syndrome, and human cultured megakaryocytes. Ultra-thin sections of the cells were labeled with antibodies directed against glycocalicin, GPIb, GPIX, and GPV. We have shown that a significant and reproducible labeling for the three GPs was associated with the alpha-granule membrane, accounting for approximately 10% of the total labeling. Furthermore, GPIb labeling appears Willebrand factor (vWF). After thrombin activation, vWF remained close to the limiting membrane of the open canalicular system (OCS), suggesting an early association of both receptor and ligand. Plasma membrane and alpha-granule labeling was virtually absent from the Bernard-Soulier platelets (characterized by a GPIb deficiency), thus proving the specificity of the reaction. In Gray platelets (storage granule deficiency syndrome), the small residual alpha- granules were also occasionally labeled for GPIb, GPIX, and GPIX. Cultured megakaryocytes that displayed the classical GPIb distribution, eg, demarcation and plasma membranes, exhibited also a discrete labeling associated to the alpha-granules. In conclusion, this study shows that, evenly for these three GPs, the alpha-granule membrane mirrors the plasma membrane composition. This might occur through an endocytotic process affecting each plasma membrane protein to a different extent and could have a physiologic relevance in further presentation of a receptor bound to its alpha-granule ligand to the platelet surface.

Intracellular localization of glycoprotein VI in human platelets and its surface expression upon activation

“…Interestingly, the localization of GPVI in resting platelets was quite similar to that of the major platelet GPs such as GPIb, GPIIb-IIIa and GPIV, with distribution observed not only on the surface plasma membrane but also on the membranes of the OCS and a-granules (Suzuki et al, 1992(Suzuki et al, , 1996aBerger et al, 1993Berger et al, , 1996Wencel-Drake et al, 1993;Nurden et al, 1994Nurden et al, , 1996Nurden et al, , 1999. In the present study, the rate of intracellular distribution of GPVI was estimated to be 35AE4 ± 3AE2% (mean ± SD) of the total and may be larger than that of GPIIb-IIIa (Woods et al, 1986).…”

Activation during preparation of therapeutic platelets affects deterioration during storage: a comparative flow cytometric study of different production methods

“…Two previous studies found a small increase in GPIba expression on PRP-PC platelets immediately after preparation which subsequently fell (Bode, 1990;Michelson et al, 1988). Whether this represents a redistribution of GPIba from intracellular pools (Berger et al, 1996), as suggested by Michelson (1988), or whether it is an artefact of the analysis, is unclear. Both groups reported the simultaneous appearance of a GPIba-negative population, and exclusion of these platelets from the flow cytometric analysis could give an apparent rise in the overall level of GPIba per platelet in the residual GPIba-positive population.…”

Ultrastructural analysis of the distribution of the vitronectin receptor (αvβ3) in human platelets and megakaryocytes reveals an intracellular pool and labelling of the α‐granule membrane

“…Studies performed on the platelets of a patient with type I Glanzmann's thrombasthenia also confirmed that VnR distribution was not influenced by the presence of GP IIb-IIIa complexes. It should be noted that Berger et al (1996) recently showed that membranes of a-granules contain GP Ib, GP IIb, GP IIIa, GP IV, GP V and GP IX, and represent a mirror image of the plasma membrane. Our results suggest that VnR should be added to this list.…”