Sphingosine-1-phosphate (S1P) is a potent lipid mediator that performs several roles [
1]. Sphingosine kinase 1 (Sphk1) or sphingosine kinase 2 produce S1P from its precursor sphingosine; meanwhile, S1P phosphatase and S1P lyase (Sgpl) revert into sphingosine and 2-hexadecenal and phospho-ethanolamine, respectively [
2]. Red blood cells (RBCs) uptake S1P [
3,
4,
5], while S1P may also be produced within the cells through Sphk1 [
2]. Since RBCs contain Sphk1 but no S1P-degrading enzymes [
6], S1P is abundantly stored in RBCs [
7], as well as in platelets [
8] and the endothelium [
9,
10]. S1P performs several functions and regulates many cellular processes, including cell growth, proliferation, migration, and apoptosis [
11,
12,
13,
14]. In recent papers, S1P has been discussed concerning the RBC adaptation mechanism to SARS-COVID-19 infection [
15]. In RBCs, S1P promotes deoxygenated haemoglobin (deoxyHb), which anchors to band 3, the most abundant membrane protein in RBCs, thereby increasing glycolysis flux, 2,3-diphosphoglycerate (2,3 DPG) levels [
16], and ATP release [
17]. RBCs release ATP under reduced oxygen tensions and following deformation, to modulate vasodilation [
18]. The pathway underlying ATP release from RBCs involves several proteins, such as G proteins, adenylyl cyclase (AC) and cyclic AMP-dependent protein kinase A [
18], which are a cystic fibrosis transmembrane conductance regulator and protein pannexin, respectively [
19,
20]. Alzheimer's disease (AD) is a pathology characterised by senile plaques in several regions of the central nervous system (CNS), which are frequently correlated with areas of neurodegeneration [
21]. Amyloid beta (Aβ) peptides, which are major protein components in the plaques, consist of 39–43 amino acid peptides that originate from a more significant transmembrane protein, amyloid precursor protein (APP). Aβ neurotoxicity has been associated with peptide self-aggregation, which leads to the formation of amyloid-like fibrils [
22] and eventually to neuronal cell death through apoptosis. However, recent studies have shown that soluble forms of Aβ exhibit stronger neurotoxicity, and in the monomeric form, Aβ may be responsible for the neurodegeneration observed in AD [
23,
24]. Aβ has been found in blood at nanomolar concentrations and is abundantly produced by platelets [
25]. RBCs encounter Aβ peptides at the luminal surface level of brain capillaries [
26] and seem to only interact with monomeric Aβ peptides [
27]. Aβ alters RBC metabolism and induces RBC death [
28,
29,
30,
31,
32,
33,
34] through a signaling pathway involving protein kinase C [
35,
36]. Evidence from epidemiological data indicates a close association between vascular and AD pathology [
37]. However, experimental studies suggest that Aβ can reduce cerebral blood flow (CBF), inducing neurovascular dysfunction and increasing the brain's susceptibility to ischemia [
38]. Therefore, we are interested in determining whether RBCs contribute to the AD pathogenesis. Previous studies have reported decreased S1P levels in AD tissues and plasma [
39,
40]. S1P protects neuronal cells from apoptosis [
41], notably in response to Aβ [
42]. Moreover, a recent paper demonstrated that S1P abrogates neuronal Ca2+ dyshomeostasis induced by toxic Aβ cells [
43].
Based on the importance of vascular dysfunction in AD pathology, in this study, we investigated the protective role of S1P against Aβ peptides on ATP release in RBCs.