Tales of tails: regulation of telomere length and telomerase activity during lymphocyte development, differentiation, activation, and aging

Summary: Telomerase activity and the regulation of telomere length are factors which have been implicated in the control of cellular replication. These variables have been examined during human lymphocyte development, differentiation, activation, and aging. It was found that telomere length of peripheral blood CD4⁺ T cells decreases with age as well as with differentiation from naive to memory cells in vivo , and decreases with cell division in vitro. These results provide evidence that telomere length correlates with lymphocyte replicative history and residual replicative potential. In contrast, telomere length appears to increase during tonsil B-cell differentiation and germinal center (GC) formation in vivo. It was also found that telomerase activity is highly regulated during T-cell development and B-cell differentiation in vivo , with high levels of telomerase activity expressed in thymocytes and GC B cells, and low levels of telomerase activity in resting mature peripheral blood lymphocytes. Finally, resting lymphocytes retain the ability to upregulate telomerase activity upon activation, and this capacity does not appear to decline with age. Although the precise role of telomerase in lymphocyte function remains to be elucidated, telomerase may contribute to protection from telomere shortening in T and B lymphocytes, and may thus play a critical role in lymphocyte development, differentiation and activation. The future study of study telomerase and its regulation of telomere length may enhance our understanding of bow the replicative lifespan is regulated in lymphocytes.     

A selective effect of naloxone on heterosynaptic C-fibre-mediated inhibitions in the rat dorsal horn

The effect of naloxone on C-primary afferent-mediated inhibitions of C-fibre-evoked activity in deep dorsal horn neurones has been examined in decerebrate-spinal rats. The same C-afferents that evoke activity in a given neurone can inhibit that C-evoked activity (homosynaptic inhibition), and C-afferent input can also inhibit the activity evoked in dorsal horn neurones by other C-afferents (heterosynaptic inhibition). Naloxone was found to selectively reverse heterosynaptic C-mediated inhibitions without affecting homosynaptic inhibitions. In several neurones the heterosynaptic inhibitions were completely abolished by naloxone. These results show that homo- and heterosynaptic C-mediated inhibitions operate by different mechanisms and that, at least in some neurones, endogenous opioids are likely to be the major inhibitory transmitters involved in producing the heterosynaptic inhibition of the activity evoked by one C-input by another C-input.     

Effects of lesions of the histaminergic tuberomammillary nucleus on spontaneous sleep in rats

STUDY OBJECTIVES: Extensive evidence suggests that histaminergic neurons promote wakefulness. Histaminergic neurons are found exclusively in the tuberomammillary nucleus (TMN), and electrolytic lesions of the posterior hypothalamus, where the TMN resides, produce intense hypersomnolence. However, electrolytic lesions disrupt fibers of passage, and the effects of fiber-sparing, cell-specific TMN lesions on sleep and wakefulness are unknown. Hence, we placed cell-specific lesions in the TMN to determine its role in spontaneous wakefulness. DESIGN: TMN neurons in rats are relatively resistant to excitotoxins. Hence, we ablated them using saporin conjugated to hypocretin 2, which ablates hypocretin receptor-bearing neurons such as TMN neurons. One to 2 weeks after bilateral injections of Hcrt2-SAP into Sprague-Dawley rats, we correlated loss of TMN neurons with changes in sleep. SETTING: N/A PARTICIPANTS: N/A INTERVENTIONS: N/A MEASUREMENTS AND RESULTS: Four days after injections with hypocretin-2-saporin, the number of TMN neurons was markedly decreased, and most were lost after 12 days, as determined by immunohistochemistry for adenosine deaminase, a marker of TMN neurons. Nearby nonhistaminergic neurons were similarly ablated. Rats with an average 82.5% loss of TMN cells (determined 2 weeks after injection) did not have marked changes in total sleep amounts compared to saline-treated rats 1 or 2 weeks following the injection, except for a slight decrease in rapid eye movement sleep during the lights-on period for the first week only. The percentage of remaining TMN neurons positively correlated with the average duration of wake bouts during the lights-off period. CONCLUSION: The absence of gross changes in sleep after extensive loss of histaminergic neurons suggests that this system is not critical for spontaneous wakefulness.     

The Src kinase Lyn is a negative regulator of mast cell proliferation

Previous investigators have reported that deletion of the protein tyrosine kinase Lyn alters mast cell (MC) signaling responses but does not affect or reduces the cytokine-mediated proliferation of mouse bone marrow-derived MC (BMMC) precursors and of mature MC. We observed that Lyn-deficient mice have more peritoneal MC than wild-type (WT) mice. Studies to explore this unexpected result showed that Lyn(-/-) BM cells expand faster than WT cells in response to interleukin (IL)-3 and stem-cell factor over the 4-5 weeks required to produce a >95% pure population of granular, receptor with high affinity for immunoglobulin E-positive BMMC. Furthermore, differentiated Lyn(-/-) BMMC continue to proliferate more rapidly than WT BMMC and undergo less apoptosis in response to cytokine withdrawal. Additionally, Lyn(-/-) BMMC support greater IL-3-mediated phosphorylation of the prosurvival kinase, Akt, and the proliferative kinase, extracellular-regulated kinase 1/2. These results identify Lyn as a negative regulator of murine MC survival and proliferation.     

Skeletal muscle mitochondrial function and lean body mass in healthy exercising elderly

BACKGROUND: The decline in muscle mass (sarcopenia) with aging may be related to a decline in mitochondrial function. However, investigators have yet to reach a consensus as to whether a decline in mitochondrial function can be attenuated by physical activity has yet to reach a consensus. METHODS: Using dynamic 31PMRS to measure mitochondrial function, we measured baseline Phosphocreatine (PCr), inorganic phosphate (Pi), phosphodiester (PDE), [ADP], pH and recovery times (t(1/2)) for PCr and [ADP] following exercise, in 45 older (73+/-4 years, SD), and 20 younger subjects (25+/-4 years, SD) who were matched for body mass across high and low activity levels and within age and sex groupings. RESULTS: Baseline PCr, and Pi, were lower, and PDE higher in the older subjects compared to younger subjects (all P<0.01). The t(1/2)(ADP) was longer in older subjects (P<0.001) controlling for age and sex in the low activity group (P=0.02). In the older low activity groups, t(1/2)(PCr) was longer than high activity groups. Higher PDE levels were positively correlated with longer t(1/2)(PCr) in the older low activity females (both P<0.05). CONCLUSIONS: Our data suggests that mitochondrial function declines with age in healthy, exercising elderly adults and that the decline appears to be influenced by the level of physical activity.     

Sunday Canyon virus, a new ungrouped agent from the tick Argas (A.) cooleyi in Texas.

A new arbovirus was isolated from Texas, U.S.A., populations of the Cliff Swallow parasits Argas (Argas) cooleyi Kohls and Hoogstraal, 1960. The virus, named Sunday Canyon, is serological urelated to any of 185 arbovirus strains or 20 other viral agents with which it was compared. Morphologically it resembles Bunyamwera viruses and, in common with them, is sensitive to lipid solvents and acid pH, and apparently possesses RNA. Although considerably resistant to a temperature of 41.5 degrees C, it rapidly loses infectivity when incubated at 56 degrees C. It is lethal for newborn white mice and infective for the Vero and Antheraea eucalypti cell lines. Sundays Canyon virus is the second tick-associated, Bunyamwera virus-like agent known from North America and the third virus to be reported from A. cooleyi in Texas.     

Wheat germ agglutinin enhances EPSCs in cultured postnatal rat hippocampal neurons by blocking ionotropic quisqualate receptor desensitization.

1. The effect of the lectin wheat germ agglutinin (WGA), an inhibitor of ionotropic quisqualate receptor desensitization, on both evoked and spontaneous fast excitatory postsynaptic events was examined in cultured postnatal rat hippocampal neurons with the use of whole cell recordings. 2. WGA, at 580 nM, potentiated evoked fast excitatory postsynaptic currents (EPSCs) by increasing the amplitudes by 100 +/- 27% (mean +/- SE) and the time constant of decay from 5.8 +/- 0.6 to 7.9 +/- 0.5 ms. The increases in these parameters were not accompanied by changes in the current-voltage (I-V) relationship or pharmacological profile of the fast EPSCs. 3. WGA did not alter the amplitude or time course of decay of inhibitory postsynaptic currents (IPSCs), and it did not alter neuronal input resistance or action potentials. 4. WGA increased the amplitude of spontaneous fast miniature EPSCs (MEPSCs), defined as spontaneous EPSCs recorded in the presence of tetrodotoxin, by 53 +/- 11% and increased the time required to decay to 50% of the peak amplitude by 48 +/- 23%. These changes were not associated with a change in the rate of MEPSC occurrence. 5. These results suggest that WGA augments hippocampal excitatory postsynaptic events via a postsynaptic mechanism. The results further imply that ionotropic quisqualate receptor desensitization can modulate the amplitude and time course of decay of fast excitatory synaptic events. Thus desensitization may be one factor that regulates fast excitatory synaptic transmission.     

Functional differences between human cutaneous mast cells and basophils: a comparison of morphine-induced histamine release

Intravenous administration of morphine sulfate often produces urticarial and hypotensive reactions associated with elevations in plasma histamine. The source of this histamine and mechanisms controlling its release are poorly understood. Previous studies of morphine-induced histamine release compared human leukocytes to rat peritoneal mast cells. The effects of morphine on human cutaneous mast cells has not been examined. We studiedin vitro histamine release from human basophils and human skin preparations containing cutaneous mast cells to evaluate their relative, contribution to the pharmacologic effects of morphine.Human skin mast cell preparations showed dosedependent histamine release over a morphine concentration range of 1.5×10^–5 to 4.5×10^–3 M, with peak release occurring at 5×10^–4 M, with peak release occurring at 5×10^–4 M. Clinically, morphine sulfate is usually injected as a 1.5×10^–2 M solution. Histamine release was calcium dependent and equivalent to that obtained with 3 and 10 mM strontium. Morphologic examination revealed degranulation and exocytosis occurring in morphine-stimulated tissue but not in specimens exposed to buffer alone. Lactate dehydrogenase levels did not increase following morphine incubation, thus supporting a noncytolytic mechanism of histamine release.Basophils, in contrast, showed no significant histamine release from exposure to morphine up to 10^–2 M. Concanavalin A, as a positive control in these same preparations, produced a mean histamine release of 21.0%.Our studies indicate distinct functional differences between human skin mast cell and human blood basophil responses to morphine sulfate. We conclude that the cutaneous and systemic reactions to morphine sulfate probably result from the release of histamine from mast cells rather than from basophils.This study was supported by: National Institutes of Health Grants 2-T32 AMO7153, 5-RO1 AI18615, AI 15557, HL 25831, American Society of Anesthesiologists Starter Grant 1283, and a grant from the Bramble Foundation.     

The dexamethasone suppression test and pituitary-adrenocortical function

The dexamethasone suppression test (DST) as now commonly carried out in psychiatric settings yields "abnormal" results in many conditions including the healthy state. To determine whether the DST accurately identifies patients with physiologically meaningful increases in pituitary-adrenocortical activity, we compared DST results to baseline urinary cortisol level. Thirty-four psychiatric inpatients underwent a 24-hour urine collection and then a DST using 1 or 2 mg of dexamethasone. With the common 1-mg DST, 24-hour urinary cortisol levels in nonsuppressors and suppressors did not differ. With the 2-mg DST, however, nonsuppressors had significantly higher urinary cortisol levels than suppressors, and all nonsuppressors had urinary cortisol levels above the normal range. Thus, the 1-mg DST may not identify the heuristically important subgroup of psychiatric patients who have a pathophysiologically meaningful alteration in pituitary-adrenal regulation.