A Circadian Rhythm in both Complement Cascade (ComC) Activation and Sphingosine-1-Phosphate (S1P) Levels in Human Peripheral Blood Supports a Role for the ComC–S1P Axis in Circadian Changes in the Number of Stem Cells Circulating in Peripheral Blood

Abstract

The number of hematopoietic stem/progenitor cells (HSPCs) circulating in peripheral blood (PB) is regulated by a circadian rhythm, and more HSPCs circulate in PB in the morning hours than at night. Different mechanisms have been proposed that might regulate this process, including changes in tonus of β-adrenergic innervation of bone marrow (BM) tissue. Our group reported that in mice circadian changes in the number of HSPCs circulating in PB correlates with diurnal activation of the complement cascade (ComC) and that the mice deficient in C5 component of ComC (C5-KO mice) do not show circadian changes in the number of circulating HSPCs in PB. We also reported the existence of a gradient between PB and BM of a bioactive phosphosphingolipid, sphingosine-1-phosphate (S1P), which is a major PB chemottractant for BM-residing HSPCs. Based on these observations, we investigated activation of the ComC and the level of S1P in the PB of 66 healthy volunteers. We found that both ComC activation and the S1P level undergo changes in a circadian cycle. While the ComC becomes highly activated during deep sleep at 2 am, S1P becomes activated later, and its highest level is observed at 8 am, which precedes circadian egress of HSPCs from BM into PB. In sum, circadian activation of the ComC–S1P axis releases HSPCs from BM into PB.

Plasma levels of melatonin in dilated cardiomyopathy

“…Melatonin levels in plasma samples were measured by using an enzyme-linked immunoassay (enzyme-linked immunosorbent assay kit, Cloud-clone Corp., Houston, TX) according to the manufacturer's protocol. 20 Briefly, 50 μL of the plasma samples and the serially diluted standards were applied into the each well, and each reagent was added and incubated and then measured at 450 nm with a microplate reader (SpectraMax i3, Molecular Devices, Sunnyvale, CA). The concentrations of the melatonin were calculated by using the standard curve.…”

Novel Evidence that Purinergic Signaling - Nlrp3 Inflammasome Axis Regulates Circadian Rhythm of Hematopoietic Stem/Progenitor Cells Circulation in Peripheral Blood

“…Interestingly, we also demonstrated that the plasma level of S1P fluctuates in patients in a circadian rhythm-dependent manner, with the peak in the early morning hours and the nadir late at night [8]. This fluctuation in S1P level can be explained by activation of the ComC due to hypoxia during deep sleep, which by generating C5b-C9 (also known as membrane attack complex, MAC) releases S1P from red blood cells and activated platelets [8].…”

“…The circadian changes in the number of circulating HSPCs in PB were the subject of several excellent studies showing a peak in the early morning hours and a nadir at night [5][6][7][8][9][10][11][12][13]. This phenomenon has been attributed to diurnal changes in tonus of the vegetative nerves that innervate BM tissue as a result of external light and dark cycles [4,9,10].…”

“…Circadian rhythms are internal processes that regulate the sleepwake cycle and repeat every 24 h. These processes are driven by a circadian clock and have been evolutionarily established in plants, fungi, bacteria, and animals, including mice and humans [1][2][3][4][5]. It is well known that this intrinsic circadian clock regulates all aspects of diurnal behavior and physiology, which includes melatonin secretion by the pineal gland, body temperature, and the plasma level of cortisol in mammals [5][6][7][8].…”

“…However, diurnal release of HSPCs from bone marrow (BM) into PB is also regulated by three evolutionarily ancient serum proteolytic cascades, the complement cascade (ComC), the coagulation cascade (CoaC), and the fibrinolytic cascade (FibC), whose activation is triggered in a circadian manner during deep-sleep hypoxia in the late-night hours [1,8,[11][12][13]. This pattern of activation correlates with diurnal fluctuations in the level of the bioactive phosphosphingolipid sphingosine-1-phosphate in PB, which is a potent chemoattractant for HSPCs and mediates their egress from BM into the circulation [8,14]. Recent evidence from our laboratories indicates that an important role in triggering stress-related or pharmacological mobilization of HSPCs is played by extracellular adenosine triphosphate (ATP), a crucial mediator of the purinergic signaling network [15][16][17].…”