Circadian cell cycle variations of erythro- and myelopoiesis in humans

The Autonomic Nervous System Pulls the Strings to Coordinate Circadian HSC Functions

As for many other adult stem cells, the behavior of hematopoietic stem and progenitor cells (HSPCs) is subjected to circadian regulatory patterns. Multiple HSPC functions, such as proliferation, differentiation or trafficking exhibit time-dependent patterns that require a tight coordination to ensure daily blood cell production. The autonomic nervous system, together with circulating hormones, relay circadian signals from the central clock-the suprachiasmatic nucleus in the brain-to synchronize HSC niche physiology according to light/darkness cycles. Research over the last 20 years has revealed how specific neural signals modulate certain aspects of circadian HSC biology. However, only recently some studies have started to decipher the cellular and molecular mechanisms that orchestrate this complex regulation in a time-dependent fashion. Here we firstly review some of the recent key findings illustrating how different neural signals (catecholaminergic or cholinergic) regulate circadian HSC egress, homing, maintenance, proliferation, and differentiation. In particular, we highlight the critical role of different neurotransmitter receptors in the bone marrow microenvironment to channel these neural signals and regulate antagonistic processes according to circadian cues and organismal demands. Then, we discuss the potential biological meaning of HSC circadian regulation and its possible utility for clinical purposes. Finally, we offer our perspective on emerging concepts in HSC chronobiology.

Daily light and darkness onset and circadian rhythms metabolically synchronize hematopoietic stem cell differentiation and maintenance: The role of bone marrow norepinephrine, tumor necrosis factor, and melatonin cycles

Hematopoietic stem and progenitor cells (HSPCs) are essential for daily mature blood cell production, host immunity, and osteoclast-mediated bone turnover. The timing at which stem cells give rise to mature blood and immune cells while maintaining the bone marrow (BM) reservoir of undifferentiated HSPCs and how these opposite tasks are synchronized are poorly understood. Previous studies revealed that daily light onset activates norepinephrine (NE)-induced BM CXCL12 downregulation, followed by CXCR4⁺ HSPC release to the circulation. Recently, we reported that daily light onset induces transient elevations of BM NE and tumor necrosis factor (TNF), which metabolically program BM HSPC differentiation and recruitment to replenish the blood. In contrast, darkness onset induces lower elevations of BM NE and TNF, activating melatonin production, which metabolically reprograms HSPCs, increasing their short- and long-term repopulation potential, and BM maintenance. How the functions of BM-retained HSPCs are influenced by daily light and darkness cycles and their clinical potential are further discussed.

Storage Iron Turnover from a New Perspective

BACKGROUND/AIMS

Storage iron turnover has remained poorly understood since 1953. In addition, errors in measurements of the storage iron turnover rate (SIT) by ferrokinetics have been detected and the causes of those errors need to be elucidated.

METHODS

A new, computer-assisted method, "serum ferritin kinetics," was introduced for the quantitation of ferritin iron and hemosiderin iron. Ferrokinetics and non-ferrokinetic methods were used to determine the body iron turnover rate.

RESULTS AND CONCLUSION

Using serum ferritin kinetics, patients with normal iron stores and iron overload were found to have 2 iron pathways between ferritin and hemosiderin: recovery of ferritin taking iron from hemosiderin in iron mobilization and iron transformation from ferritin to hemosiderin in iron deposition. In addition, underestimation of the SIT by ferrokinetics was confirmed by comparing SIT by ferrokinetics with the standard SIT as the sum of SIT of 3 major iron-storing cells. This underestimation was caused by extra radio-iron fixation to red cells. Ferrokinetics does not give the actual body iron turnover due to the behavioral difference between radio-iron and pre-existing body iron. Recent findings on ferritin and hemosiderin iron turnover will be a potential tool for the diagnosis and therapy of hematological disorders.

Circadian Influence on Metabolism and Inflammation in Atherosclerosis

Many aspects of human health and disease display daily rhythmicity. The brain's suprachiasmic nucleus, which interprets recurring external stimuli, and autonomous molecular networks in peripheral cells together, set our biological circadian clock. Disrupted or misaligned circadian rhythms promote multiple pathologies including chronic inflammatory and metabolic diseases such as atherosclerosis. Here, we discuss studies suggesting that circadian fluctuations in the vessel wall and in the circulation contribute to atherogenesis. Data from humans and mice indicate that an impaired molecular clock, disturbed sleep, and shifting light-dark patterns influence leukocyte and lipid supply in the circulation and alter cellular behavior in atherosclerotic lesions. We propose that a better understanding of both local and systemic circadian rhythms in atherosclerosis will enhance clinical management, treatment, and public health policy.

Measuring stem cell circadian rhythm

Circadian rhythms are biological rhythms that occur within a 24-h time cycle. Sleep is a prime example of a circadian rhythm and with it melatonin production. Stem cell systems also demonstrate circadian rhythms. This is particularly the case for the proliferating cells within the system. In fact, all proliferating cell populations exhibit their own circadian rhythm, which has important implications for disease and the treatment of disease. Stem cell chronobiology is particularly important because the treatment of cancer can be significantly affected by the time of day a drug is administered. This protocol provides a basis for measuring hematopoietic stem cell circadian rhythm for future stem cell chronotherapeutic applications.

The Cinderella syndrome: why do malaria-infected cells burst at midnight?

An interesting quirk of many malaria infections is that all parasites within a host – millions of them – progress through their cell cycle synchronously. This surprising coordination has long been recognized, yet there is little understanding of what controls it or why it has evolved. Interestingly, the conventional explanation for coordinated development in other parasite species does not seem to apply here. We argue that for malaria parasites, a critical question has yet to be answered: is the coordination due to parasites bursting at the same time or at a particular time? We explicitly delineate these fundamentally different scenarios, possible underlying mechanistic explanations and evolutionary drivers, and discuss the existing corroborating data and key evidence needed to solve this evolutionary mystery.

Minor diurnal and activity-induced variations in daytime peripheral blood platelet counts do not have any major impact on platelet yield by platelet apheresis

Physical activity alters systemic levels of several angioregulatory cytokines that affect microvascular endothelial cells and can be assumed to influence vascular permeability. This may alter platelet release to the bone marrow microcirculation and thereby the levels of circulating platelets. We investigated effects of physical activity on angioregulatory chemokines (CXCL8, 9, 10 and 11) and peripheral blood platelet counts before and after intensive physical activity in young adults, and also compared platelet yields obtained by platelet apheresis performed in the morning and in the afternoon in 20 healthy donors. Physical activity increased serum CXCL10 levels and platelet counts but did not alter the other chemokine concentrations. In the apheresis donors, there was only a minor increase in platelet counts during the day, and the platelet yields did not differ significantly between platelet concentrates collected early in the morning and late in the afternoon. In conclusion, minor intra-individual variations in platelet counts do not seem to have major influence on platelet yields by platelet apheresis.

The 4th dimension and adult stem cells: Can timing be everything?

The rotation of the earth on its axis influences the physiology of all organisms. A highly conserved set of genes encoding the core circadian regulatory proteins (CCRP) has evolved across species. The CCRP acts through transcriptional and post-transcriptional mechanisms to direct the oscillatory expression of genes essential for key metabolic events. In addition to the light:dark cycle, the CCRP expression can be entrained by changes in feeding and physical activity patterns. While mammalian CCRP were originally associated with the central clock located within the suprachiasmatic nucleus of the brain, there is a growing body of evidence documenting the presence of the CCRP in peripheral tissues. It is now evident that the CCRP play a role in regulating the proliferation, differentiation, and function of adult stem cells in multiple organs. This concise review highlights findings concerning the role of the CCRP in modulating the adult stem cell activities. Although the manuscript focuses on hematopoietic stem cells (HSCs), bone marrow-derived mesenchymal stem cells (BMSCs), adipose-derived stem cells (ASCs) and cancer stem cells, it is likely that the contribution of the CCRP merits consideration and evaluation in all stem cell pathways.

Circadian rhythms influence hematopoietic stem cells

PURPOSE OF REVIEW

Hematopoiesis is tightly regulated in the bone marrow through the microenvironment, soluble factors from the circulation, and neural inputs from the autonomic nervous system. Most physiological processes are not uniform but rather vary according to the time of day. There is increasing evidence showing the impact of biological rhythms on the traffic of hematopoietic stem cells (HSCs) and their proliferation and differentiation capacities.

RECENT FINDINGS

Recent evidence supports the role of the sympathetic nervous system in the regulation of HSC behavior, both directly and through supporting stromal cells. In addition, the sympathetic nervous system transduces circadian information from the central pacemaker in the brain, the suprachiasmatic nucleus, to the bone marrow microenvironment, directing circadian oscillations in hematopoiesis and HSC migration.

SUMMARY

HSC traffic and hematopoiesis do not escape the circadian regulation that controls most physiological processes. Clinically, the timing of stem cell harvest or infusion may impact the yield or engraftment, respectively, and may result in better therapeutic outcomes.

Induction of circadian rhythm in cultured human mesenchymal stem cells by serum shock and cAMP analogs in vitro

Circadian clocks have been shown to operate developmentally in mouse and human hematopoietic stem and progenitor cells in vivo, but little is known about their possible oscillations in vitro. Here, we show that repeated circadian oscillations could be induced in both cultured bone marrow-derived mesenchymal- and adipose-derived stem cells (MSCs and ASCs, respectively) by serum shock. In particular, the novel finding of rhythmic clock gene expression induced by cAMP analogs showed similarities as well as differences to serum-induced oscillations. Rhythmic PER1 expression was found in serum-shocked MSCs, suggesting the phosphorylation status of PER1 is important for its activity in circadian rhythms. Furthermore, immunofluoresent staining showed that the localization of PER1 was dependent on the level of PER1 expression. These inducible self-sustained circadian clocks in primary cultures of human MSCs in vitro with rhythmic changes in expression levels, phosphorylation, and localization of clock protein, PER1, may be of importance for maintaining the induced oscillations in stem cells. Therefore, the established cell models described here appear to be valuable for studying the molecular mechanism driving and coordinating the circadian network between stem and stromal cells.

Circadian variations in clock gene expression of human bone marrow CD34+ cells

Time-dependent variations in clock gene expression have recently been observed in mouse hematopoietic cells, but the activity of these genes in human bone marrow (BM) has so far not been investigated. Since such data can be of considerable clinical interest for monitoring the dynamics in stem/progenitor cells, the authors have studied mRNA expression of the clock genes hPer1 , hPer2, hCry1, hCry2, hBmal1, hRev-erb alpha, and hClock in human hematopoietic CD34-positive (CD34( +)) cells. CD34(+) cells were isolated from the BM samples obtained from 10 healthy men at 6 times over 24 h. In addition, clock gene mRNA expression was analyzed in the whole BM in 3 subjects. Rhythms in serum cortisol, growth hormone, testosterone, and leukocyte counts documented that subjects exhibited standardized circadian patterns. All 7 clock genes were expressed both in CD34(+) cells and the whole BM, with some differences in magnitude between the 2 cell populations. A clear circadian rhythm was shown for hPer1, hPer2, and hCry2 expression in CD34(+) cells and for hPer1 in the whole BM, with maxima from early morning to midday. Similar to mouse hematopoietic cells, h Bmal1 was not oscillating rhythmically. The study demonstrates that clock gene expression in human BM stem/progenitor cells may be developmentally regulated, with strong or weaker circadian profiles as compared to those reported in other mature tissues.

Circadian expression of clock genes in purified hematopoietic stem cells is developmentally regulated in mouse bone marrow

OBJECTIVE

Clock genes are known to mediate circadian rhythms in the central nervous system and peripheral organs. Although they are expressed in mouse hematopoietic progenitor and stem cells, it is unknown if they are related to circadian rhythms in these cells. We therefore investigated the 24-hour patterns in the activity of several clock genes in the bone marrow (BM) side population (SP) primitive stem cells, and compared these 24-hour patterns to clock gene variations in the whole BM and liver.

METHODS

Cells were obtained from 84 B6D2F(1) mice in three replicate experiments on the second day after release into constant darkness from a standardizing light-dark schedule. mRNA expression of clock genes was measured with quantitative reverse transcriptase polymerase chain reaction.

RESULTS

mPer2 displayed circadian rhythms in SP cells, whole BM, and liver cells. mPer1 and mRev-erb alpha showed a circadian rhythm in whole BM and liver, but not SP cells. mBmal1 was not expressed rhythmically in SP cells, nor in the whole BM, contrary to rhythms observed in the liver.

CONCLUSIONS

With the exception of mPer2, most clock genes studied in primitive hematopoietic SP stem cells were not oscillating in a fully organized circadian manner, which is similar to immature cells in rapidly proliferating organs, such as the testis and thymus. These findings indicate that circadian clock gene expression variations in BM are developmentally regulated.

Circadian regulation of cell cycle and apoptosis proteins in mouse bone marrow and tumor

Proapoptotic drugs such as docetaxel displayed least toxicity and highest antitumor efficacy following dosing during the circadian rest phase in mice, suggesting that cell cycle and apoptotic processes could be regulated by the circadian clock. In study 1, mouse bone marrow and/or tumor were obtained every 4 h for 24 h in C3H/HeN mice with or without MA13/C mammary adenocarcinoma in order to determine the circadian patterns in cell-cycle phase distribution and BCL-2 anti-apoptotic protein expression. In study 2, mouse bone marrow from B6D2F1 mice was sampled every 3 h for 24 h in order to confirm the BCL-2 rhythm and to study its relation with 24 h changes in the expression of proapoptotic BCL-2-associated X protein (BAX) protein and clock genes mPer2, mBmal1, mClock, and mTim mRNAs. The rhythms in G1-, S- or G2/M-phase cells were shifted in tumor compared with bone marrow. In the tumor, the mean proportion of G2/M-phase cells increased by 75% from late rest to late activity span (P from cosinor = 0.001). No 24 h rhythm was found for BCL-2 in tumors. In contrast to this, in the bone marrow, mean BCL-2 expression varied 2.8-fold in B6D2F1 mice (P=0.025) and 3- or 4.5-fold in tumor-bearing and nontumor-bearing C3H/HeN mice, with a peak during the early rest span (P=0.024 and P<0.001, respectively). BAX varied fivefold during the 24 h span with a major peak occurring near mid-activity (P=0.007). The mean mRNAs of mPer2, mClock, and mBmal1 varied twofold to threefold over the 24 h, with high values during the activity span (P<0.05). In the tumor, the circadian organization in cell-cycle phase distribution was shifted and BCL2 rhythm was ablated. Conversely, a molecular circadian clock likely regulated BCL-2 and BAX expression in the bone marrow, increasing cellular protection against apoptosis during the rest span.

Circatidal variation in epithelial cell proliferation in the mussel digestive gland and stomach

Epithelial cell renewal in mussel ( Mytilus galloprovincialis, Lmk) digestive gland and stomach was investigated by bromodeoxyuridine (BrdU) immunohistochemistry. Mussels were exposed to 4 mg BrdU/l seawater continuously. Starting at 6 h after treatment, samples were collected every 2 h for 2 days and BrdU labelling was estimated by direct counting at the light microscope, with values being noted per thousand BrdU-positive cells. BrdU-positive reaction was observed in the nuclei of digestive, basophilic, duct and stomach cells, and in haemocytes. Cell renewal in digestive diverticula was synchronised following a circatidal pattern: BrdU labelling increased during low tide and decreased during high tide. Clearcut mitotic figures were identified in digestive cells, thereby confirming that mature cell types proliferate, in agreement with results from immunohistochemistry for proliferating cell nuclear antigen and BrdU. Epithelial cell renewal in the stomach also appeared to be synchronised.

Rhythms in human bone marrow and blood cells

In 24h studies of bone marrow (BM), circadian stage-dependent variations were demonstrated in the proliferative activity of BM cells from subsets of 35 healthy diurnally active men. On an average, the percentage of total BM cells in deoxyribonucleic acid (DNA) synthesis phase was 188% greater at midday than at midnight (circadian rhythm: p = 0.018; acrophase or peak time of 13: 16h). Patients with malignant disease (n = 15) and a normal cortisol circadian rhythm showed higher fractions of BM cells in S-phase at midday. Colony-forming units--granulocyte/macrophage (CFU-GM), an indicator of myeloid progenitor cells, showed the same circadian variation as DNA S-phase (average range of change or ROC = 136%; circadian rhythm: p < 0.001; acrophase of 12:09h). Deoxyribonucleic acid S-phase and CFU-GM in BM both showed a circannual rhythm (p = 0.015 and 0.008) with an identical acrophase of August 12. The daily peak in BM glutathione content, a tripeptide involved in cellular defense against cytotoxic damage, preceded BM proliferative peaks by 4-5 h (ROC = 31-90%; circadian rhythm: p = 0.05; acrophase of 08:30h). Myeloid (ROC = 57%; circadian rhythm: p = 0.056; acrophase at 08:40h) and erythroid (ROC = 26%; circadian rhythm: p = 0.01; acrophase of 13:01h) precursor cells were positively correlated (r = 0.41; p < 0.001), indicating a circadian temporal relationship and equal influence on S-phase of total BM cells. Yield of positive selected CD34+ progenitor stem cells also showed significant circadian variation (ROC = 595%; circadian rhythm: p = 0.02; acrophase of 12:40h). Thus, the temporal synchrony in cell cycling renders BM cells more sensitive at specific times to hematopoietic growth factors and cell cycle-specific cytotoxic drugs. Moreover, proper timing of BM harvesting may improve progenitor cell yield. When using marker rhythms in the blood to allow for individualized timing of BM procedures, the times of low values in white blood corpuscles, neutrophils, and lymphocytes and high values in cortisol were predictive of the times of highest BM erythroid, myeloid, and total S-phase numbers occurring in the following 12 h.

Cyclic red blood cell destruction in thalassemia

A retrospective analysis of time series of hemoglobin (Hb) destruction of 24 children (11 males and 13 females) with thalassemia from the age of 6 to 12 years showed that the Hb destruction rate typically oscillated with an average period of 50 days. A possible relation between the periodism and the severity of the disease is also suggested.

Expression of mPer1 and mPer2, two mammalian clock genes, in murine bone marrow

Although circadian variations in hematopoiesis have been well documented, the molecular mechanism of the circadian rhythms remains elusive. To determine if a clock system exists in bone marrow to mediate the circadian rhythms, we analyzed the expression of mPer1 and mPer2, both mouse homologues of the Drosophila period gene and known regulators of the clock system, in murine bone marrow by relative quantitative reverse transcriptase-polymerase chain reaction (RT-PCR). We demonstrated that both genes were expressed in bone marrow. Furthermore, the expression patterns of mPer1 and mPer2 in total bone marrow cells exhibited two peaks over a 24-h period. In contrast, the expression patterns of these two genes in the Gr-1-positive cells isolated from bone marrow mainly contributed to one of the two peaks. These results indicate that a clock system exists in bone marrow and suggest that the circadian rhythms in bone marrow are lineage- and/or differentiation stage-dependent.

Variation in cell yield and proliferative activity of positive selected human CD34+ bone marrow cells along the circadian time scale

Variations in cell yield and proliferative activity of human bone marrow (BM) progenitor cells were determined with flow cytometry along the 24-h (circadian) time scale. Equal volumes of BM were aspirated every 5 h, altogether 5 times in 5 healthy men. An average 6-fold higher yield of positive selected CD34+ cells occurred in each subject when BM was aspirated during the daytime and late afternoon, while a lower yield occurred during the night. Using all CD34+ cell yield data normalized to percentage of mean, a significant time-effect was found by ANOVA (p = 0.02) and a significant circadian rhythm was detected by the least-squares fit of a 24 h cosine (p = 0.02). The 95% confidence limits of the acrophase (time of highest values) were computed to be at midday between 10:24 and 14:48 h. A highly significant correlation (p = 0.001) was found between proliferation of positive selected CD34+ cells and the more mature myeloid precursor cells from the same BM aspirates, suggesting a common temporal pattern along the circadian time scale. However, no correlation was demonstrated between proliferation and cell yield of CD34+ selected cells, suggesting that mechanisms other than variation in proliferation may cause the circadian rhythm in stem cell yield. These circadian variations in stem cell yield and proliferation suggest that proper timing within 24 h may potentially be important regarding outcome from progenitor cell harvesting and treatment with haematopoietic growth factors.