The mystery and magic of glia: a perspective on their roles in health and disease

In this perspective, I review recent evidence that glial cells are critical participants in every major aspect of brain development, function, and disease. Far more active than once thought, glial cells powerfully control synapse formation, function, and blood flow. They secrete many substances whose roles are not understood, and they are central players in CNS injury and disease. I argue that until the roles of nonneuronal cells are more fully understood and considered, neurobiology as a whole will progress only slowly.     

Caffeine promotes ultraviolet B-induced apoptosis in human keratinocytes without complete DNA repair

In response to ultraviolet B damage, keratinocytes undergo apoptosis to eliminate damaged cells, thereby preventing tumorigenic transformation. Caffeine, the most widely consumed psychoactive substance, produces complex pharmacological actions; it has been shown to be chemopreventive in non-melamona skin cancer in mice through increasing apoptosis. Here we have investigated the molecular and cellular mechanisms in the pro-apoptotic effect of caffeine on UVB-irradiated human HaCaT keratinocytes. Pretreatment with caffeine increased UVB-induced apoptosis in HaCaT cells. Caffeine blocked UVB-induced Chk1 phosphorylation. In addition, similar to the effect of the PI3K inhibitor LY294002, caffeine also inhibited phosphorylation of AKT and up-regulation of COX-2, two critical oncogenic pathways in skin tumorigenesis. However, phosphorylation of EGFR or ERK was unaffected. Inhibiting ATR pathways by siRNA targeting ATR had little effect on UVB-induced apoptosis or AKT activation, indicating that the inhibitory effect of caffeine on apoptosis and the AKT pathway does not require the ATR pathway. Inhibiting AKT by caffeine blocked UVB-induced COX-2 up-regulation. Expression of constitutively active AKT that was not inhibited by caffeine was found to protect cells from caffeine-promoted apoptosis post-UVB irradiation, indicating that AKT is an essential inhibitory target for caffeine to promote apoptosis. Caffeine specifically sensitized cells with unrepaired DNA damage to UVB-induced apoptosis. These findings indicate that in HaCaT keratinocytes, inhibiting the AKT/COX-2 pathways through an ATR-independent pathway is a critical molecular mechanism by which caffeine promotes UVB-induced apoptosis of unrepaired keratinocytes for elimination.     

DNA strand break metabolism in human lymphocytes: a reevaluation

Recent findings concerning the presumed existence of single-strand breaks (SSB) in quiescent human peripheral blood lymphocytes (PBL) are discussed in relation to the role of poly(ADP-ribosyl)ation in DNA strand break metabolism. It is argued that the activation of poly(ADP-ribose)polymerase (ADPRP) by a DNA-damaging agent is not indicative of an obligatory role of poly(ADP-ribosyl)ation in DNA repair. From this it follows that SSB induced by different strand-breaking agents might be removed by either ADPRP-dependent or ADPRP-independent DNA repair pathways.     

Caffeine, performance, and metabolism during repeated Wingate exercise tests

Investigations examining the ergogenicand metabolic influence of caffeine during short-term high-intensityexercise are few in number and have produced inconsistent results. Thisstudy examined the effects of caffeine on repeated bouts ofhigh-intensity exercise in recreationally active men. Subjects(n = 9) completed four 30-s Wingate(WG) sprints with 4 min of rest between each exercise bout on twoseparate occasions. One hour before exercise, either placebo (Pl;dextrose) or caffeine (Caf; 6 mg/kg) capsules were ingested. Caf ingestion did not have any effect on poweroutput (peak or average) in the first two WG tests and had a negative effect in the latter two exercise bouts. Plasmaepinephrine concentration was significantly increased 60 min after Cafingestion compared with Pl; however, this treatment effect disappearedonce exercise began. Caf ingestion had no significant effect on bloodlactate, O₂ consumption, oraerobic contribution at any time during the protocol. After the secondWingate test, plasma NH₃concentration increased significantly from the previous WG test and wassignificantly higher in the Caf trial compared with Pl. These datademonstrate no ergogenic effect of caffeine on power output duringrepeated bouts of short-term, intense exercise. Furthermore, there was no indication of increased anaerobic metabolism after Caf ingestion with the exception of an increase inNH₃ concentration.

     

The mystery of Etruscan origins: novel clues from Bos taurus mitochondrial DNA

The Etruscan culture developed in Central Italy (Etruria) in the first millennium BC and for centuries dominated part of the Italian Peninsula, including Rome. The history of the Etruscans is at the roots of Mediterranean culture and civilization, but their origin is still debated: local or Eastern provenance? To shed light on this mystery, bovine and human mitochondrial DNAs (mtDNAs) have been investigated, based on the well-recognized strict legacy which links human and livestock populations. In the region corresponding to ancient Etruria (Tuscany, Central Italy), several Bos taurus breeds have been reared since historical times. These breeds have a strikingly high level of mtDNA variation, which is found neither in the rest of Italy nor in Europe. The Tuscan bovines are genetically closer to Near Eastern than to European gene pools and this Eastern genetic signature is paralleled in modern human populations from Tuscany, which are genetically close to Anatolian and Middle Eastern ones. The evidence collected corroborates the hypothesis of a common past migration: both humans and cattle reached Etruria from the Eastern Mediterranean area by sea. Hence, the Eastern origin of Etruscans, first claimed by the classic historians Herodotus and Thucydides, receives strong independent support. As the Latin philosopher Seneca wrote: Asia Etruscos sibi vindicat (Asia claims the Etruscans back).     

Caffeine and human cerebral blood flow: a positron emission tomography study

Positron emission tomography (PET) was used to quantify the effect of caffeine on whole brain and regional cerebral blood flow (CBF) in humans. A mean dose of 250 mg of caffeine produced approximately a 30% decrease in whole brain CBF; regional differences in caffeine effect were not observed. Pre-caffeine CBF strongly influenced the magnitude of the caffeine-induced decrease. Caffeine decreased paCO2 and increased systolic blood pressure significantly; the change in paCO2 did not account for the change in CBF. Smaller increases in diastolic blood pressure, heart rate, plasma epinephrine and norepinephrine, and subjectively reported anxiety were also observed.     

Unraveling the mystery of cancer metabolism in the genesis of tumor-initiating cells and development of cancer

Robust anaerobic metabolism plays a causative role in the origin of cancer cells; however, the oncogenic metabolic genes, factors, pathways, and networks in genesis of tumor-initiating cells (TICs) have not yet been systematically summarized. In addition, the mechanisms of oncogenic metabolism in the genesis of TICs are enigmatic. In this review, we discussed multiple cancer metabolism-related genes (MRGs) that are overexpressed in TICs and are responsible for inducing pluripotent stem cells. Moreover, we summarized that oncogenic metabolic genes and onco-metabolites induce metabolic reprogramming, which switches normal mitochondrial oxidative phosphorylation to cancer anaerobic metabolism, triggers epigenetic, genetic, and environmental alterations, drives the generation of TICs, and boosts the development of cancer. Importantly, cancer metabolism is controlled by positive and negative metabolic regulators. Positive oncogenic metabolic regulators, including key oncogenic metabolic genes, onco-metabolites, hypoxia, and an acidic environment, promote oncogenic metabolic reprogramming and anaerobic metabolism. However, dysfunction of negative metabolic regulators, including defects in p53, PTEN, and LKB1-AMPK-mTOR pathways, enhances cancer metabolism. Loss of the metabolic balance results in oncogenic metabolic reprogramming, genesis of TICs, and tumorigenesis. Collectively, this review provides new insight into the role and mechanism of these oncogenic metabolisms in the genesis of TICs and tumorigenesis. Accordingly, targeting key oncogenic genes, onco-metabolites, pathways, networks, and the acidic cancer microenvironment appears to be an attractive strategy for novel anti-tumor treatment.     

The mystery of the mystery of common genetic diseases

Common monogenic genetic diseases, ones that have unexpectedly high frequencies in certain populations, have attracted a great number of conflicting evolutionary explanations. This paper will attempt to explain the mystery of why two particularly extensively studied common genetic diseases, Tay Sachs disease and cystic fibrosis, remain evolutionary mysteries despite decades of research. I review the most commonly cited evolutionary processes used to explain common genetic diseases: reproductive compensation, random genetic drift (in the context of founder effect), and especially heterozygote advantage. The latter process has drawn a particularly large amount of attention, having so successfully explained the elevated frequency of sickle cell anemia in malaria-endemic areas. However, the empirical evidence for heterozygote advantage in other common genetic diseases is quite weak. I introduce and illustrate the significance of a hierarchy of genetic disease phenomena found within the genetic disease explanations, which include the phenomena: single mutation variants of a common genetic disease, single genetic diseases, and classes of diseases with related phenotypic effects. I demonstrate that some of the confusion over the explanations of common genetic diseases can be traced back to confusions over which phenomena are being explained. I proceed to briefly evaluate the existing evidence for two common human genetic diseases: Tay Sachs disease and cystic fibrosis. The above considerations will ultimately shed light on why these diseases’ evolutionary explanations remain so deeply unresolved after so such a great volume of research.     

Caffeine metabolism in Coffea arabica and other species of coffee

High performance liquid chromatography has been used to measure the quantities of caffeine, theobromine, and theophylline in aqueous extracts of endosperm from immature and mature fruits of Coffea arabica and six other species of Coffea. Caffeine was the alkaloid present in largest amounts and, with one exception, in concentrations that were broadly similar in immature and mature fruit. The highest concentrations of caffeine were found in C. canephora at 35.1 and 24.5 mg g⁻¹, respectively, in immature and mature endosperm. The lowest concentrations were in C. bengalensis, where caffeine was not detected in extracts from mature fruit. [8-³H]Caffeine was metabolised relatively slowly by immature endosperm of C. arabica and C. canephora. In contrast, C. dewevrei, C. eugenioides, C. stenophylla, C. salvatrix and C. bengalensis all appeared to metabolise [8-³H]caffeine much more rapidly, as the percentage recovery of the applied label was much lower and there was more extensive incorporation of radioactivity into theobromine, theophylline, 3-methylxanthine and two unidentified polar metabolites. The endogenous caffeine concentrations and the metabolism data indicate that there may be marked differences in the rate of turnover of caffeine in the various species of Coffea. Potential sources of material for the production of naturally decaffeinated coffee are discussed.     

Effect of Caffeine on DNA Synthesis in Mammalian Cells

Alkaline sucrose sedimentation studies of DNA from mouse lymphoma cells (L5178Y) treated with caffeine have demonstrated the following effects. Caffeine (at a concentration of 1.6 mM) does not introduce strand breaks into preformed DNA nor does it inhibit the rejoining of γ-ray-induced strand breaks. Although it does not affect the over-all rate of DNA synthesis, pulse labeling experiments show that the DNA strands synthesized in its presence are smaller than those made in its absence. This could be the result of (a) DNA being made in shorter replicating units or (b) small gaps in the daughter DNA strands within normal-sized replicating units. These two alternative models were indirectly distinguished as follows. After a pulse label with thymidine-³H in the presence of caffeine, cells were incubated without caffeine in bromodeoxyuridine (BrdUrd). During this incubation, growing strands are elongated and hypothetical gaps (model b) filled in with bromuracil (BrUra)-substituted DNA. The BrUra-containing DNA segments will now be of different lengths on the two models. With smaller replicating units (a) the “elongation segments” will be somewhat smaller than but the same order of magnitude as those in untreated cells, whereas with small gaps (b) the “filled-in gap segments” would be expected to be at least an order of magnitude smaller. The BrUra-containing regions of DNA can be selectively broken open by exposing the cells to light at 313 nm. The exposure required to break open the BUra-substituted regions is inversely related to, and hence gives a measure of, the size of these regions. In caffeine-treated cells these regions were found to be somewhat smaller than but of comparable size with those in untreated cells; this is consistent with the DNA being synthesized in smaller units and argues against the presence of small gaps in the daughter strands.