Hypoxia induces purinergic receptor signaling to disrupt endothelial barrier function

P2Y1 receptor in Alzheimer's disease

Alzheimer's disease is the most frequent form of dementia characterized by the deposition of amyloid-beta plaques and neurofibrillary tangles consisting of hyperphosphorylated tau. Targeting amyloid-beta plaques has been a primary direction for developing Alzheimer's disease treatments in the last decades. However, existing drugs targeting amyloid-beta plaques have not fully yielded the expected results in the clinic, necessitating the exploration of alternative therapeutic strategies. Increasing evidence unravels that astrocyte morphology and function alter in the brain of Alzheimer's disease patients, with dysregulated astrocytic purinergic receptors, particularly the P2Y1 receptor, all of which constitute the pathophysiology of Alzheimer's disease. These receptors are not only crucial for maintaining normal astrocyte function but are also highly implicated in neuroinflammation in Alzheimer's disease. This review delves into recent insights into the association between P2Y1 receptor and Alzheimer's disease to underscore the potential neuroprotective role of P2Y1 receptor in Alzheimer's disease by mitigating neuroinflammation, thus offering promising avenues for developing drugs for Alzheimer's disease and potentially contributing to the development of more effective treatments.

LPS induces SGPP2 to participate metabolic reprogramming in endothelial cells

Sepsis often causes organ dysfunction and is manifested in increased endothelial cell permeability in blood vessels. Early-stage inflammation is accompanied by metabolic changes, but it is unclear how the metabolic alterations in the endothelial cells following lipopolysaccharide (LPS) stimulation affect endothelial cell function. In this study, the effects of 1 μg/ml of LPS on the metabolism of human umbilical vein endothelial cells (HUVECs) were investigated, and the metabolic changes after LPS stimulation were explained from the perspective of mRNA expression, chromatin openness and metabolic flux. We found changes in the central metabolism of endothelial cells after LPS stimulation, such as enhanced glycolysis function, decreased mitochondrial membrane potential, and increased production of reactive oxygen species (ROS). Sphingolipid metabolic pathways change at the transcriptome level, and sphingosine-1-phosphatase 2 (SGPP2) was upregulated in LPS-stimulated endothelial cells and zebrafish models. Overexpression of SGPP2 improved cell barrier function, enhanced mitochondrial respiration capacity, but also produced oxidative respiration chain uncoupling. In addition, SGPP2 overexpression inhibited the degradation of HIF-1α protein. The molecular and biochemical processes identified in this study are not only beneficial for understanding the metabolic-related mechanisms of LPS-induced endothelial injury, but also for the discovery of general therapeutic targets for inflammation and inflammation-related diseases.

Could hypoxia rehabilitate the osteochondral diseased interface? Lessons from the interplay of hypoxia and purinergic signals elsewhere

The osteochondral unit comprises the articular cartilage (90%), subchondral bone (5%) and calcified cartilage (5%). All cells present at the osteochondral unit that is ultimately responsible for matrix production and osteochondral homeostasis, such as chondrocytes, osteoblasts, osteoclasts and osteocytes, can release adenine and/or uracil nucleotides to the local microenvironment. Nucleotides are released by these cells either constitutively or upon plasma membrane damage, mechanical stress or hypoxia conditions. Once in the extracellular space, endogenously released nucleotides can activate membrane-bound purinoceptors. Activation of these receptors is fine-tuning regulated by nucleotides' breakdown by enzymes of the ecto-nucleotidase cascade. Depending on the pathophysiological conditions, both the avascular cartilage and the subchondral bone subsist to significant changes in oxygen tension, which has a tremendous impact on tissue homeostasis. Cell stress due to hypoxic conditions directly influences the expression and activity of several purinergic signalling players, namely nucleotide release channels (e.g. Cx43), NTPDase enzymes and purinoceptors. This review gathers experimental evidence concerning the interplay between hypoxia and the purinergic signalling cascade contributing to osteochondral unit homeostasis. Reporting deviations to this relationship resulting from pathological alterations of articular joints may ultimately unravel novel therapeutic targets for osteochondral rehabilitation. At this point, one can only hypothesize how hypoxia mimetic conditions can be beneficial to the ex vivo expansion and differentiation of osteo- and chondro-progenitors for auto-transplantation and tissue regenerative purposes.

Purinergic signaling: A gatekeeper of blood-brain barrier permeation

This review outlined evidence that purinergic signaling is involved in the modulation of blood-brain barrier (BBB) permeability. The functional and structural integrity of the BBB is critical for maintaining the homeostasis of the brain microenvironment. BBB integrity is maintained primarily by endothelial cells and basement membrane but also be regulated by pericytes, neurons, astrocytes, microglia and oligodendrocytes. In this review, we summarized the purinergic receptors and nucleotidases expressed on BBB cells and focused on the regulation of BBB permeability by purinergic signaling. The permeability of BBB is regulated by a series of purinergic receptors classified as P2Y₁, P2Y₄, P2Y₁₂, P2X4, P2X7, A₁, A_2A, A_2B, and A₃, which serve as targets for endogenous ATP, ADP, or adenosine. P2Y₁ and P2Y₄ antagonists could attenuate BBB damage. In contrast, P2Y₁₂-mediated chemotaxis of microglial cell processes is necessary for rapid closure of the BBB after BBB breakdown. Antagonists of P2X4 and P2X7 inhibit the activation of these receptors, reduce the release of interleukin-1 beta (IL-1β), and promote the function of BBB closure. In addition, the CD39/CD73 nucleotidase axis participates in extracellular adenosine metabolism and promotes BBB permeability through A₁ and A_2A on BBB cells. Furthermore, A_2B and A₃ receptor agonists protect BBB integrity. Thus, the regulation of the BBB by purinergic signaling is complex and affects the opening and closing of the BBB through different pathways. Appropriate selective agonists/antagonists of purinergic receptors and corresponding enzyme inhibitors could modulate the permeability of the BBB, effectively delivering therapeutic drugs/cells to the central nervous system (CNS) or limiting the entry of inflammatory immune cells into the brain and re-establishing CNS homeostasis.