[Pulmonary arterial hypertension, bone marrow, endothelial cell precursors and serotonin]

Pulmonary hypertension: Pathophysiology beyond the lung

Pulmonary hypertension (PH) is classically considered a disease of pulmonary vasculature which has been the predominant target for drug development and PH therapy. Despite significant advancement in recent years in identification of new drug targets and innovative treatment strategies, the prognosis of PH remains poor, with median survival of 5 years. Recent studies have demonstrated involvement of neuroinflammation, altered autonomic and gastrointestinal functions and increased trafficking of bone marrow-derived cells in cardiopulmonary pathophysiology. This has led to the proposal that PH could be considered a systemic disease involving complex interactions among many organs. Our objectives in this review is to summarize evidence for the involvement of the brain, bone marrow and gut in PH pathophysiology. Then, to synthesize all evidence supporting a brain-gut-lung interaction hypothesis for consideration in PH pathophysiology and finally to summarize unanswered questions and future directions to move this novel concept forward. This forward-thinking view, if proven by further experiments, would provide new opportunities and novel targets for the control and treatment of PH.

The Role of Serotonin beyond the Central Nervous System during Embryogenesis

Serotonin, or 5-hydroxytryptamine (5-HT), is a well-known neurotransmitter that plays vital roles in neural activities and social behaviors. Clinically, deficiency of serotonin is linked with many psychiatric disorders. Interestingly, a large proportion of serotonin is also produced outside the central nervous system (CNS). There is increasing evidence demonstrating important roles of serotonin in the peripheral tissues. Here, we will describe the multiple biological functions of serotonin in hematopoietic system, such as development of hematopoietic stem and progenitor cells (HSPCs), differentiation of hematopoietic cells, maintenance of vascular system, and relationship with hematological diseases. The roles of serotonin in inflammatory responses mediated by hematopoietic cells as well as in liver regeneration are also discussed. Our recent understandings of the impact of serotonin on hematopoietic system, immune responses, and tissue regeneration support utilization of serotonin as a potential therapeutic target for the treatment of hematological diseases and organ repair in clinic.