A lack of positive effect of enhanced vegetative nervous system tonus on mobilization of hematopoietic stem and progenitor cells in patients suffering from acute psychotic syndromes

It has been demonstrated in mice that enhanced tonus of vegetative nervous system regulates mobilization of hematopoietic stem and progenitor cells (HSPCs) into peripheral blood (PB). It is well known that HSPCs circulate under steady-state conditions at detectable levels in PB, with their numbers increasing in response to stress, inflammation, and tissue and organ injury.^1–3 Circulation of these cells under normal steady-state conditions is regulated by a circadian rhythm, with the peak of these circulating cells occurring in the early morning hours and the nadir at night.^1–4 As observed in mice exposed to daylight changes, this oscillation in HSPC levels is affected as postulated by changes in tonus of the vegetative nervous system.^4,5

HSPCs can be also mobilized into PB in an enforced manner by administration of granulocyte-colony stimulating factor (G-CSF), and it has also been shown in mice that release of these cells into PB depends critically on the vegetative nervous system.^4,5 Moreover, UDP-galactose:ceramide galactosyltransferase-deficient mice, which exhibit aberrant nerve conduction and do not release norepinephrine (NE) into the BM microenvironment, do not mobilize HSPCs in response to G-CSF. ⁴ To explain how NE signaling influences HSPC mobilization, it has been postulated that it modulates expression of stromal derived factor-1 (SDF-1) in the BM microenvironment, and such a mechanism would be consistent with the finding that administration of β2-adrenergic agonists enhances mobilization of HSPCs in both control and NE-deficient mice. ⁴ In a recent study, it has also been proposed that G-CSF increases sympathetic tonus directly via G-CSF receptors that are expressed on peripheral sympathetic neurons, which would reduce NE reuptake and increase NE availability in the BM microenvironment.⁵

However, as recently reported modification of sympathetic output does not affect G-CSF-induced mobilization in humans, as would be predicted.⁶ Specifically, normal human HSPC volunteer donors who were receiving NE reuptake inhibitors (NRI) for depression or β2-blockers because of hypertension mobilize in a similar manner as normal controls.⁶ Mobilization in these patients was neither enhanced by NRI administration nor suppressed by β2-blockers, as one would expect based on murine data reported in the literature. ^4,5

To address this intriguing issue, we analyzed levels of circulating HSPCs in patients suffering from acute psychosis, which was assessed using the MINI psychiatric examination ⁷ and The International Classification of Diseases 10^th Revision criteria (ICD-10, 1998). Enrolled in this study were 30 unrelated individuals of Polish descent, with a diagnosis of the first-episode psychosis (F20, F22, or F23) according to ICD-10, with no history of axis I psychiatric disorders other than the above mentioned psychosis, drug-naïve. The patients were compared with an ethnic- and gender-matched control group of 35 healthy volunteers without psychiatric disorders, which were excluded according to an examination by a specialist psychiatrist. The study protocol was approved by the Ethics Committee of the Pomeranian Medical University, and written informed consent was obtained from all the participants. Patients with a history of serious lifetime medical events, organic brain injuries, or drug/alcohol dependence were excluded from the study. Demographic data, family history, and history of symptoms were assessed by means of a structured interview with the patient and his/her family. Psychometric evaluation of patients was performed with Polish versions of the positive and negative syndrome scale (PANSS).⁸

Mobilization of HSPCs was evaluated by i) FACS to enumerate the number of CD34⁺, CD133⁺, CD34⁺CD45⁺Lin⁻, and CD133⁺CD45⁺Lin⁻ cells circulating in PB, which are enriched for HSPCs, as well as by ii) functional in vitro assays to detect the number of CFU-GM and BFU-E clonogenic progenitors circulating in PB, as previously described. ⁹ These cells were enumerated in psychotic patients before treatment and compared with age- and sex-matched controls.

Figure 1 A shows the number of CD34⁺, CD133⁺, CD34⁺CD45⁺Lin⁻ and CD133⁺CD45⁺Lin⁻ cells circulating in PB, and Figure 1 B shows the number of circulating CFU-GM and BFU-E clonogenic progenitors. We did not observe any significant differences in the numbers of these cells between normal controls and psychotic patients. Moreover, we employed the PANSS scale to measure the severity of psychosis and found that the number of CD34⁺CD45⁺Lin⁻ HSPCs circulating in PB (Figure 2) was negatively correlated with the score of the PANSS subscale of positive psychotic symptoms.

Figure 1. The number of HSPCs circulating in peripheral blood in patients with acute psychosis and matched controls.

Panel A – The number of CD34⁺, CD133⁺, CD34⁺CD45⁺Lin⁻ and CD133⁺CD45⁺Lin⁻ cells circulating in PB. Panel B – The number of circulating CFU-GM and BFU-E clonogenic progenitors.

Figure 2. A lack of correlation between PANSS score and the number of HSPCs circulating in peripheral blood.

PANNS score, which measures the severity of psychosis, is negatively correlated with the number of CD34⁺CD45⁺Lin⁻ HSPCs circulating in PB.

Thus, our preliminary data argue against an effect of enhanced vegetative nervous system tone on the number of HSPCs circulating in PB. Our negative data performed on patients suffering from acute psychoses somewhat corroborate data reported for normal HSPC volunteer donors that were previously treated with NRI because of depression or with β2-blockers because of high blood pressure and mobilized with G-CSF.⁶ This finding suggests that there are some clear differences between rodents and humans in the effect of the vegetative nervous system on HSPC mobilization.

During acute psychotic syndromes, patients are under the influence of several neural mediators, and it is well known that the levels of NE and dopamine are elevated in peripheral tissues and blood.¹⁰ Moreover, results from other group ¹¹ showed a higher NE turnover rate in first-episode schizophrenic patients.

However, tonus of the vegetative nervous system may play some role in circadian release of HSPCs into PB, and thus it would be interesting to study whether there are any circadian changes in the numbers of these circulating cells in patients suffering from acute psychotic syndromes compared with normal controls. Furthermore, a similar analysis of circadian circulation of HSPCs could be performed in patients medicated with NRI and β2-blockers. However, these studies should also be supported by measuring the secretion of NE and its metabolites in 24-hour-collected urine.

While considering the circadian circulation of HSPCs, one should also remember that the level of these cells in PB could be affected not only by circadian changes in vegetative nervous system tonus but also by changes in activation of the complement and coagulation cascades. These two important evolutionarily conserved cascades follow circadian changes due to a decrease in blood pH during deep sleep. ^12,13 In support of this possibility, the complement cascade is an important modulator of HSPC trafficking. ² Furthermore, there is vigorous crosstalk between the coagulation and complement cascades, which are usually simultaneously activated. In particular, it has been demonstrated that thrombin, the final product of coagulation cascade activation, is a potent activator of the C5 component of the complement cascade ¹⁴ and mobilization of HSPCs is severely impaired in C5-deficient mice. ^{9, 15}

Finally, we cannot exclude a possibility that vegetative nervous system may still affect in a positive way mobilization of HSPCs when other pro-mobilization factors are present - such as for example enhanced patient psychomotor activity or prolonged hypoxia. Nevertheless, as demonstrated in this paper enhanced vegetative tonus of nervous system alone, did not provide such pro-mobilizing stimulus for HSPCs in our patients suffering from acute psychotic syndrome. Thus our data somehow support recently published work ⁶ that mobilization of HSPCs may be differently regulated by vegetative nervous system in small rodents and humans.