Are platelets more than a model of brain neurons?

For many years, the brain was considered as a closed system protected by the blood-brain barrier (BBB), where only the hormones produced by the body can mediate the interplay between the brain and the blood. Indeed, hormones, crossing the BBB and binding to specific receptors on the brain cells, regulates neuronal and synaptic plasticity and neurogenesis [...]

Role of amyloid peptides in vascular dysfunction and platelet dysregulation in Alzheimer’s disease

Alzheimer’s disease (AD) is the most common neurodegenerative cause of dementia in the elderly. AD is accompanied by the accumulation of amyloid peptides in the brain parenchyma and in the cerebral vessels. The sporadic form of the AD accounts for about 95% of all cases. It is characterized by a late onset, typically after the age of 65, with a complex and still poorly understood aetiology. Several observations point towards a central role of cerebrovascular dysfunction in the onset of sporadic AD. According to the vascular hypothesis, AD may be initiated by vascular dysfunctions that precede and promote the neurodegenerative process. In accordance to this, AD patients show increased hemorragic or ischemic stroke risks. It is now clear that multiple bidirectional connections exist between AD and cerebrovascular disease, and in this new scenario, the effect of amyloid peptides on vascular cells and blood platelets appear to be central to AD. In this review we analyse the effect of amyloid peptides on vascular function and platelet activation and its contribution to the cerebrovascular pathology associated with AD and the progression of this disease

Increased platelet adhesion and thrombus formation in a mouse model of Alzheimer's disease

Vascular dysfunctions and Alzheimer's disease show significant similarities and overlaps. Cardiovascular risk factors (hypercholesterolemia, hypertension, obesity, atherosclerosis and diabetes) increase the risk of vascular dementia and Alzheimer's disease. Conversely, Alzheimer's patients have considerably increased predisposition of ischemic and hemorrhagic strokes. Platelets are major players in haemostasis and thrombosis and are involved in inflammation. We have investigated morphology and function of platelets in 3xTg-AD animals, a consolidate murine model for Alzheimer's disease. Platelets from aged 3xTg-AD mice are normal in number and glycoprotein expression, but adhere more avidly on matrices such as fibrillar collagen, von Willebrand factor, fibrinogen and amyloid peptides compared to platelets from age-matching wild type mice. 3xTg-AD washed platelets adherent to collagen also show increased phosphorylation of selected signaling proteins, including tyrosine kinase Pyk2, PI3 kinase effector Akt, p38MAP kinase and myosin light chain kinase, and increased ability to form thrombi under shear. In contrast, aggregation and integrin αIIbβ3 activation induced by several agonists in 3xTg-AD mice are similar to wild type platelets. These results demonstrated that Alzheimer's mutations result in a significant hyper-activated state of circulating platelets, evident with the progression of the disease

5′UTR point substitutions and N-terminal truncating mutations of ANKRD26 in acute myeloid leukemia

Thrombocytopenia 2 (THC2) is an inherited disorder caused by monoallelic single nucleotide substitutions in the 5'UTR of the ANKRD26 gene. Patients have thrombocytopenia and increased risk of myeloid malignancies, in particular, acute myeloid leukemia (AML). Given the association of variants in the ANKRD26 5'UTR with myeloid neoplasms, we investigated whether, and to what extent, mutations in this region contribute to apparently sporadic AML. To this end, we studied 250 consecutive, non-familial, adult AML patients and screened the first exon of ANKRD26 including the 5'UTR. We found variants in four patients. One patient had the c.-125T>G substitution in the 5'UTR, while three patients carried two different variants in the 5' end of the ANKRD26 coding region (c.3G>A or c.105C>G). Review of medical history showed that the patient carrying the c.-125T>G was actually affected by typical but unrecognized THC2, highlighting that some apparently sporadic AML cases represent the evolution of a well-characterized familial predisposition disorder. As regards the c.3G>A and the c.105C>G, we found that both variants result in the synthesis of N-terminal truncated ANKRD26 isoforms, which are stable and functional in cells, in particular, have a strong ability to activate the MAPK/ERK signaling pathway. Moreover, investigation of one patient with the c.3G>A showed that mutation was associated with strong ANKRD26 overexpression in vivo, which is the proposed mechanism for predisposition to AML in THC2 patients. These data provide evidence that N-terminal ANKRD26 truncating mutations play a potential pathogenetic role in AML. Recognition of AML patients with germline ANKRD26 pathogenetic variants is mandatory for selection of donors for bone marrow transplantation

Blood platelets: Circulating mirrors of neurons?

Blood platelets and resident neurons are fundamentally different cells, with peculiar features in embryological origin, function, and localization. However, they share common characteristics in subcellular organization and in protein composition.1 One of the most intriguing observations is that several proteins are typically expressed in both neurons and circulating platelets. In the latter, their concentrations are unusually high, and they are found to regulate processes such as platelet activation, hemostasis, and thrombosis

PI3K/Akt in platelet integrin signaling and implications in thrombosis

Blood platelets are anucleated circulating cells that play a critical role in hemostasis and are also implicated in arterial thrombosis, a major cause of death worldwide. The biological function of platelets strongly relies in their reactiveness to a variety of extracellular agonists that regulate their adhesion to extracellular matrix at the site of vascular injury and their ability to form rapidly growing cell aggregates. Among the membrane receptors expressed on the cell surface, integrins are crucial for both platelet activation, adhesion and aggregation. Integrin affinity for specific ligands is regulated by intracellular signaling pathways activated in stimulated platelets, and, once engaged, integrins themselves generate and propagate signals inside the cells to reinforce and consolidate platelet response and thrombus formation. Phosphatidylinositol 3-Kinases (PI3Ks) have emerged as crucial players in platelet activation, and they are directly implicated in the regulation of integrin function. This review will discuss the contribution of PI3Ks in platelet integrin signaling, focusing on the role of specific members of class I PI3Ks and their downstream effector Akt on both integrin inside-out and outside-in signaling. The contribution of the PI3K/Akt pathways stimulated by integrin engagement and platelet activation in thrombus formation and stabilization will also be discussed in order to highlight the possibility to target these enzymes in effective anti-thrombotic therapeutic strategies