Abnormal expression and subcellular distribution of subunit proteins of the AP-3 adaptor complex lead to platelet storage pool deficiency in the pearl mouse.
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The pearl mouse is a model for Hermansky Pudlak Syndrome (HPS), whose symptoms include hypopigmentation, lysosomal abnormalities, and prolonged bleeding due to platelet storage pool deficiency (SPD). The gene for pearl has recently been identified as the beta3A subunit of the AP-3 adaptor complex. The objective of these experiments was to determine if the expression and subcellular distribution of the AP-3 complex were altered in pearl platelets and other tissues. The beta3A subunit was undetectable in all pearl cells and tissues. Also, expression of other subunit proteins of the AP-3 complex was decreased. The subcellular distribution of the remaining AP-3 subunits in platelets, macrophages, and a melanocyte-derived cell line of pearl mice was changed from the normal punctate, probably endosomal, pattern to a diffuse cytoplasmic pattern. Ultrastructural abnormalities in mutant lysosomes were likewise apparent in mutant kidney and a cultured mutant cell line. Genetically distinct mouse HPS models had normal expression of AP-3 subunits. These and related experiments strongly suggest that the AP-3 complex regulates the biogenesis/function of organelles of platelets and other cells and that abrogation of expression of the AP-3 complex leads to platelet SPD. (+info)
Morphological changes of platelets following platelet aggregation induced by collagen in Japanese Black cattle with delta-storage pool deficiency.
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Electron microscopic observation was performed on platelets activated by collagen stimulation in Japanese Black cattle with delta-storage pool deficiency (delta-SPD) to identify their morphological and functional abnormalities compared from normal bovine platelets. Platelets of normal Japanese Black cattle changed their shapes to spherical and were in the phase of release reactions 5 min after the collagen (90.9 microg/ml) stimulation, and most of platelets were aggregated. On the other hand, in GSPD cattle, most of a granules were still dispersed in activated platelets, although the spherical shape change of the platelets was observed. These results suggested that there are abnormalities in the release reactions in platelets of delta-SPD cattle. (+info)
Platelet ultrastructural morphometry for diagnosis of partial delta-storage pool disease in patients with mild platelet dysfunction and/or thrombocytopenia of unknown origin. A study of 24 cases.
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BACKGROUND AND OBJECTIVE: Exact diagnosis is sometimes difficult in patients presenting with a slight bleeding diathesis, prolonged bleeding times, non-specific aggregometric abnormalities, and/or mild thrombocytopenia. The objective of this study was to evaluate the use of platelet ultrastructural morphometry in detecting a partial d-storage pool disease in such patients. DESIGN AND METHODS: Platelets from 52 patients and 15 controls were fixed immediately in glutaraldehyde in White's saline without anticoagulant and processed for transmission electron microscopy. Using computer-assisted morphometry, the size and shape of the platelets were measured, as were the size and number per platelet of the dense- and a-granules. Ultrastructural morphology of the above and other intraplatelet structures was observed. RESULTS: Twenty-four cases were diagnosed as having a partial d-storage pool disease. Mean platelet area (2.28 microm(2)) and maximum diameter (2.58 microm) were significantly greater in patients than in control subjects (1.64 microm(2) and 2. 25 microm, respectively) but discoid shape was preserved. Mean dense-granule number was decreased, both per platelet and per microm(2) of platelet area (patients 0.22 and 0.09; controls 0.42 and 0.24). Seven patients also had a marked decrease in a-granules, resulting in a significantly lower mean number of granules per microm(2 )(patients 2.43; controls 3.15). Additionally, the patients' platelets had significant increases in both lipid droplets and surface-connected canalicular system. INTERPRETATION AND CONCLUSIONS: A partial dense-granule deficiency, sometimes associated with partial a-granule deficiency, should be borne in mind faced with patients who have a slight bleeding diathesis, non-specific platelet dysfunction tests and/or mild thrombocytopenia of unknown origin. Platelet ultrastructural morphometry is useful in diagnosing this condition. (+info)
Hermansky-Pudlak syndrome type 3 in Ashkenazi Jews and other non-Puerto Rican patients with hypopigmentation and platelet storage-pool deficiency.
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Hermansky-Pudlak syndrome (HPS), consisting of oculocutaneous albinism and a bleeding diathesis due to the absence of platelet dense granules, displays extensive locus heterogeneity. HPS1 mutations cause HPS-1 disease, and ADTB3A mutations cause HPS-2 disease, which is known to involve abnormal intracellular vesicle formation. A third HPS-causing gene, HPS3, was recently identified on the basis of homozygosity mapping of a genetic isolate of HPS in central Puerto Rico. We now describe the clinical and molecular characteristics of eight patients with HPS-3 who are of non-Puerto Rican heritage. Five are Ashkenazi Jews; three of these are homozygous for a 1303+1G-->A splice-site mutation that causes skipping of exon 5, deleting an RsaI restriction site and decreasing the amounts of mRNA found on northern blotting. The other two are heterozygous for the 1303+1G-->A mutation and for either an 1831+2T-->G or a 2621-2A-->G splicing mutation. Of 235 anonymous Ashkenazi Jewish DNA samples, one was heterozygous for the 1303+1G-->A mutation. One seven-year-old boy of German/Swiss extraction was compound heterozygous for a 2729+1G-->C mutation, causing skipping of exon 14, and resulting in a C1329T missense (R396W), with decreased mRNA production. A 15-year-old Irish/English boy was heterozygous for an 89-bp insertion between exons 16 and 17 resulting from abnormal splicing; his fibroblast HPS3 mRNA is normal in amount but is increased in size. A 12-year-old girl of Puerto Rican and Italian background has the 3,904-bp founder deletion from central Puerto Rico on one allele. All eight patients have mild symptoms of HPS; two Jewish patients had received the diagnosis of ocular, rather than oculocutaneous, albinism. These findings expand the molecular diagnosis of HPS, provide a screening method for a mutation common among Jews, and suggest that other patients with mild hypopigmentation and decreased vision should be examined for HPS. (+info)
Phosphotyrosine proteins in platelets from patients with storage pool disease: direct relation between granule defects and defective signal transduction.
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BACKGROUND AND OBJECTIVES: Storage pool diseases (SPD) are heterogeneous disorders associated with an abnormal presence of intraplatelet granules, which cause mild to moderate bleeding diathesis. We investigated signaling through tyrosine phosphorylation of proteins occurring in platelets with total or partial absence of dense- and alpha-granules in response to activation. DESIGN AND METHODS: We included a patient with severe delta-SPD, a patient with severe alpha-SPD or gray platelet syndrome, and six patients with partial deficiency of dense or a-granules. SPD was confirmed by electron microscopy evaluation of platelet ultrastructure. Platelet function was evaluated by bleeding time determination and conventional aggregometry. Platelet suspensions were activated with collagen and thrombin to analyze changes in tyrosine phosphorylation of proteins by electrophoresis and Western-blotting. RESULTS: Bleeding times were prolonged in all the patients included. Aggregation responses were slightly decreased in delta-SPD and normal in the rest of patients. Tyrosine phosphorylation in platelets from patients with partial forms of SPD was equivalent to that observed in control platelets, absent in response to collagen and thrombin activation in delta-SPD, and deficient only to thrombin activation in alpha-SPD. INTERPRETATION AND CONCLUSIONS: Tyrosine phosphorylation of proteins in activated platelets is highly dependent on the substances contained in the dense-granules and moderately dependent on those contained in the alpha-granules. A minimum amount of intraplatelet granules ensures signaling through tyrosine phosphorylation of proteins. (+info)
The regulation of platelet-dense granules by Rab27a in the ashen mouse, a model of Hermansky-Pudlak and Griscelli syndromes, is granule-specific and dependent on genetic background.
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The ashen (ash) mouse, a model for Hermansky-Pudlak syndrome (HPS) and for a subset of patients with Griscelli syndrome, presents with hypopigmentation, prolonged bleeding times, and platelet storage pool deficiency due to a mutation which abrogates expression of the Rab27a protein. Platelets of mice with the ashen mutation on the C3H/HeSnJ inbred strain background have greatly reduced amounts of dense granule components such as serotonin and adenine nucleotides though near-normal numbers of dense granules as enumerated by the dense granule-specific fluorescent dye mepacrine. Thus, essentially normal numbers of platelet dense granules are produced but the granule interiors are abnormal. Collagen-mediated aggregation of mutant platelets is significantly depressed. No abnormalities in the concentrations or secretory rates of 2 other major platelet granules, lysosomes and alpha granules, were apparent. Similarly, no platelet ultrastructural alterations other than those involving dense granules were detected. Therefore, Rab27a regulates the synthesis and secretion of only one major platelet organelle, the dense granule. There were likewise no mutant effects on levels or secretion of lysosomal enzymes of several other tissues. Together with other recent analyses of the ashen mouse, these results suggest a close relationship between platelet dense granules, melanosomes of melanocytes and secretory lysosomes of cytotoxic T lymphocytes, all mediated by Rab27a. Surprisingly, the effects of the ashen mutation on platelet-dense granule components, platelet aggregation, and bleeding times were highly dependent on genetic background. This suggests that bleeding tendencies may likewise vary among patients with Griscelli syndrome and HPS with Rab27a mutations. (+info)
A clinical variant of familial Hermansky-Pudlak syndrome.
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Hermansky-Pudlak syndrome (HPS) is an autosomal recessive inherited disease consisting of (1) partial oculocutaneous albinism (with nystagmus, strabism, and visual acuity loss), (2) platelet storage pool deficiency (with bleeding diathesis), and (3) disorder of "ceroid" metabolism with a multisystem tissue lysosomal ceroid deposition. HPS is less uncommon in Puerto Rico, where the most important studies have been performed, but is a very rare disease in Europe. HPS basic defect remains unknown, even if an HPS-causing gene was identified in chromosome segment 10q23-q23.3, and several mutations have been reported. The aim of this article is to discuss, on the basis of a review of relevant literature, a new familial HPS clinical variant observed in 2 young sisters (aged 16 and 23 years old, respectively), characterized by the typical symptoms of this syndrome. Our patients also suffered from diffuse interstitial pulmonary disease and an unexpectedly increased platelet aggregation and were prone to bacterial infections. Interestingly, we observed urinary tract abnormality in the younger HPS sister and a porencephalic cyst in the older HPS sister; both of these developmental defects have been reported in the Cross syndrome (or oculocerebral hypopigmentation syndrome). It seems that in our patients, an overlapping of the phenotypic manifestations of different rare syndromes may be present. The presence of ceroid-like autofluorescent material in urinary sediment together with the histologic aspects and the autofluorescence of oral mucosa biopsy are consistent with a ceroid-like lipofuscin storage. HPS should be carefully tested for in suspected cases to prevent the severe visual impairment, rapidly progressive pulmonary fibrosis, and other complications associated with this disorder. (+info)
Mutation analysis of HPS1, the gene mutated in Hermansky-Pudlak syndrome, in patients with isolated platelet dense-granule deficiency.
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BACKGROUND AND OBJECTIVES: Isolated platelet dense granule (PDG) deficiency is a heterogeneous disorder frequently found among patients with mild to moderate bleeding diatheses. However, the molecular basis of this disorder is unknown. Genes involved in other rare bleeding disorders with associated reduction in the numbers of platelet dense-granules may play a role in isolated PDG deficiency. Among such genes, HPS1 is known to play a key role in the genesis of PDG and as many as 18 different HPS1 mutations have been identified in patients with Hermansky-Pudlak syndrome. Recently, we have identified subjects with one HPS1 heterozygous mutation displaying significant reductions in PDG without the clinical phenotype of Hermansky-Pudlak syndrome. This suggested that HPS1 mutations could be involved in isolated PDG deficiency. DESIGN AND METHODS: We sequenced all coding exons, and flanking intron regions of HPS1 in 16 patients with mild to severe PDG deficiency, most of whom had mild bleeding episodes. Nine patients reported a familial history of bleeding diathesis with PDG deficiency. We also evaluated the prevalence of HPS1 variations in 215 controls. Transmission electron microscopy was used to evaluate the number and morphology of PDG from patients and selected controls. RESULTS: No patient with PDG deficiency carried severe mutations of the HPS1 gene. We identified 6 previously described and 5 new polymorphisms in the HPS1 gene. Platelet electron microscopy in controls carrying these polymorphisms revealed that they did not significantly modify the number or morphology of PDG. INTERPRETATION AND CONCLUSIONS: Mutations affecting the HPS1 gene play a minor role in isolated PDG deficiency. These results support a molecular heterogeneity responsible for the number and morphology of PDG. (+info)