Porphyrin accumulation in the harderian glands of female Syrian hamster results in mitochondrial damage and cell death

Analysis of constant tissue remodeling in Syrian hamster Harderian gland: intra-tubular and inter-tubular syncytial masses

The Syrian hamster Harderian gland (HG) has a marked sexual dimorphism and exhibits an extraordinary rate of porphyrinogenesis. The physiological oxidative stress, derived from constant porphyrin production, is so high that the HG needs additional survival autophagic mechanisms to fight against this chronic exposure, provoking the triggering of a holocrine secretion in female glands that forms two types of secretory masses: intra-tubular-syncytial and inter-tubular-syncytial masses. The aim of this work was to study the development of this inter-tubular holocrine secretion. To approach this task, we have considered that the steps developed during the formation of the so-called invasive masses consist of the growth of epithelial cells, cell detachment from the basal lamina and invasion of surrounding tissues. The presence of these masses, particularly in the female HG, are closely linked to sexual dimorphism in redox balance and to alterations in the expression of certain factors such as cytokeratins, P-cadherin, matrix metalloproteinases, cathepsin H, proliferating cell nuclear antigen, p53, CD-31 and vascular endothelial growth factor, which seem to be involved in tissue remodeling. The results document unusual mechanisms of secretion in Syrian hamster HG: an extraordinary system of massive secretion through the conjunctive tissue, disrupting the branched structure of the gland.

Hereditary cataract of the Nakano mouse: Involvement of a hypomorphic mutation in the coproporphyrinogen oxidase gene

The Nakano cataract (NCT) is a recessive disorder in the mouse linked to the nct locus on chromosome 16. In this study, we positionally cloned the critical gene in the nct locus. Herein, we report that cataracts in the BALB/c-nct/nct mouse are caused by a hypomorphic mutation in the coproporphyrin oxidase gene (Cpox), encoding the enzyme responsible for catalyzing oxidative decarboxylation of the heme precursor, coproporphyrinogen III, in the heme biosynthetic pathway. BALB/c-nct/nct mice are homozygous for a G to T nucleotide substitution in the Cpox gene, which results in a p.R380L amino acid substitution in the CPOX protein. The CPOX isoform with the p.R380L substitution retained only 15% of the activity of the wild type isoform. BALB/c-nct/nct mice had excessive accumulation of coproporphyrin III in the lens. The NCT phenotype was normalized by the introduction of a wild type Cpox transgene. The mechanisms by which impairment of CPOX leads to lens opacity in the NCT are elusive. However, our data illuminate a hitherto unanticipated involvement of the heme biosynthesis pathway in lens physiology.

Physiological autophagy in the Syrian hamster Harderian gland

The Syrian hamster Harderian gland (HG) displays a huge porphyrins metabolism with sexual dimorphism. Even in male Syrian hamsters with much lower porphyrins concentration than female HG, this activity is higher than in the liver. The damage derived from constant porphyrin production, displayed by reactive oxygen species, forces the gland to develop mechanisms that allow it to continue with its normal physiology. The survival strategy of the Harderian gland is mainly based on autophagic processes that are considered as a constant renovation system. Our results show different autophagy mechanisms in Syrian hamster HG, macroautophagy and other lysosomal-like processes such as chaperone-mediated autophagy, depending on sex and probably related to oxidative stress status. This chapter describes the methods used by us to characterize the autophagic processes that are being physiologically developed by this organ under normal conditions.

Proteome Profiling in the Rat Harderian Gland

The Harderian gland is an orbital gland located behind the ocular bulb in most terrestrial vertebrates probably functioning for production of lipid secretion to protect the eye. We herein present a protein reference database of the rat Harderian gland that may serve as analytical tool for future proteomic work, report lipid and porphyrin handling cascades, address sequence conflicts and report structures that have not been so far described by proteomics methods.

Recent advances in mammalian haem transport

Haem is a structural component of numerous cellular proteins and contributes greatly to iron metabolic processes in mammals. Haem-carrier protein 1 (HCP1) has recently been cloned and characterized as a putative transporter in the apical region of the duodenum, and is responsible for uptake of haem into the gut cells. Its expression is regulated pre- and post-translationally in hypoxic and iron-deficient mice, respectively. The identification of HCP1 has revealed the long-sought mechanism by which haem--an important source of dietary iron--is absorbed from the diet by the gut. Feline leukaemic virus receptor (FLCVR) and ABC transporter ABCG2, characterized in haematopoietic cells, have also recently been shown to export haem, particularly under stress. FLVCR protects developing erythroid cells from haem toxicity during the early stages of differentiation, and ABCG2 averts protoporphyrin accumulation (particularly under hypoxic conditions). These haem-efflux proteins are expressed in other cells and tissues including the intestine where they might function as apical haem exporters to prevent toxicity in the enterocytes.

Survival mechanisms in a physiological oxidative stress model

The Syrian hamster Harderian gland has as the remarkable feature of an extraordinary rate of porphyrin production, even higher than the liver. The low activity of the last enzyme of the route gives rise to the accumulation of the uncomplex porphyrins in the female glands. Moreover, due to the localization of the Harderian gland, porphyrins exposed to light produce reactive oxygen species and, thus, the gland presents a physiological oxidative stress, with a great number of sings of degeneration, but without compromising the gland integrity. The appearance of abnormal features in this gland was largely described in the past, but the significance is interpreted for the first time in this study. We have found that autophagic processes are the first result of an elevated porphyrin metabolism, as it is observed in both sexes. This mechanism is considered, in this case, as a constant renovation system that allows the normal gland activity to be sustained. Furthermore, there is a second procedure, invasive processes toward connective tissue, which even occasionally reach blood vessels with intravasation of damaged gland components into the bloodstream. This effect is a consequence of a strong oxidative stress environment that is mainly observed in the female gland, resembling to tumoral progression. Both mechanisms, autophagy and invasive processes, have to be implied in the maintenance of the gland integrity.

The Stem Cell Marker Bcrp/ABCG2 Enhances Hypoxic Cell Survival through Interactions with Heme

Our studies demonstrate that the ABC transporter and marker of stem and progenitor cells known as the breast cancer resistance protein (BCRP or ABCG2) confers a strong survival advantage under hypoxic conditions. We show that, under hypoxia, progenitor cells from Bcrp(-)/(-)mice have a reduced ability to form colonies as compared with progenitor cells from Bcrp(+/+) mice. Blocking BCRP function in Bcrp(+/+) progenitor cells markedly reduces survival under hypoxic conditions. However, blocking heme biosynthesis reverses the hypoxic susceptibility of Bcrp(-/-) progenitor cells, a finding that indicates that heme molecules (i.e. porphyrins) are detrimental to Bcrp(-/-) cells under hypoxia. BCRP specifically binds heme, and cells lacking BCRP accumulate porphyrins. Finally, Bcrp expression is up-regulated by hypoxia, and we demonstrate that this up-regulation involves the hypoxia-inducible transcription factor complex HIF-1. Collectively, our findings suggest that cells can, upon hypoxic demand, use BCRP to reduce heme or porphyrin accumulation, which can be detrimental to cells. Our findings have implications for the survival of stem cells and tumor cells in hypoxic environments.

Characterization of melatonin high-affinity binding sites in purified cell nuclei of the hamster (Mesocricetus auratus) harderian gland

In the present paper, binding of melatonin to purified cell nuclei from harderian glands of male and female hamsters was assessed. Binding of 125I-melatonin to cell nuclei fulfills the criteria for binding to a receptor site. Binding kinetics exhibit properties such as dependence on time and temperature as well as reversibility, saturability, high affinity and specificity. The dissociation constants (K(D)) and the number of binding sites (B(max)) for the binding of 125I-melatonin to harderian gland nuclei were 260 +/- 56 pm and 12.2 +/- 0.8 fmol/mg protein in male glands, and 280 +/- 43 pm and 9.8 +/- 0.6 fmol/mg protein in female glands, respectively. Competition experiments showed IC50 values for melatonin of 250 +/- 45 pm and 290 +/- 68 pm in male and female glands, respectively. Other indoleamines such as N-acetylserotonine and 5-metoxytryptamine showed IC50 values in the micromolar range, suggesting that the binding sites are specific for melatonin. Hill analyses of the data show nH values of 0.96-0.98, suggesting the existence of a single class of binding sites. These data indicate that specific 125I-melatonin binding sites exist in the cell nuclei of Harderian glands in male as well as in female hamsters, without significant differences between them. The K(D) and B(max) values obtained from the binding in both sexes correlates well with the concentration of melatonin described in these respective Harderian glands. It is hypothesized that the nuclear binding sites of melatonin here described could be a physiological melatonin receptor, which may be involved in the genomic-dependent antioxidant effects of melatonin on hamster Harderian glands elsewhere reported.

Effects of continuous light exposure on antioxidant enzymes, porphyric enzymes and cellular damage in the Harderian gland of the Syrian hamster

The Syrian hamster Harderian gland (HG), an organ present in the male two secretory cell types (type-I and type-II cells), is physiologically exposed to high oxidative stress because of high concentrations of porphyrins and their precursor, 5-aminolevulinic acid. Because of its juxtaorbital location, the HG is accessible to light, and subject to phototoxic effects of these substances. After having previously demonstrated circadian rhythms in antioxidant enzymes, porphyric enzymes and oxidative damage of proteins and lipids, as well as influences of melatonin on these parameters, we have now studied the effects of continuous light (LL), which suppresses melatonin secretion by the pineal gland. Measurements were performed in two different circadian phases, in order to detect the presence or absence of day/night differences. In LL, no differences between circadian phases of subjective day and subjective night were demonstrable for 5-aminolevulinate synthase, 5-aminolevulinate dehydratase, porphobilinogen deaminase, or superoxide dismutase; temporal differences in glutathione reductase and catalase were markedly diminished, whereas all these parameters showed marked day/night differences in the rats exposed to a light/dark cycle of 14:10. In LL, oxidative damage to lipids was minimally effected, while protein damage was enhanced. LL also caused a reduction in the percentage of type-II cells. Therefore, cell differentiation in the HG does not seem to be controlled only by the androgen, but, unexpectedly, also by melatonin.

HPLC measurement of harderoporphyrin in the harderian glands of rodents as a biomarker for sub-lethal or chronic arsenic exposure

An improved HPLC method has been established for the measurement of harderoporphyrin (HP) in the harderian gland of rats and mice. Groups of female Wistar rats were given a single oral dose of sodium arsenite at 0, 0.5 or 5.0 mg As(III)/kg body weight, or a slurry of arsenic-contaminated soil at equivalent dose rates and the animals were sacrificed 96 h after dosing. A group of C57BL/6J female mice were chronically exposed to drinking water containing 500 microg As(V)/l of sodium arsenate ad libitum for over 2 years. Porphyrins were measured in the harderian glands of rats and mice. Our results suggest that HP and the alteration of the porphyrin profile in the harderian glands of rodents is a highly sensitive biomarker for both single sub-lethal and chronic arsenic exposure.

Effects of delta-aminolevulinic acid and melatonin in the harderian gland of female Syrian hamsters

Effects of delta-aminolevulinic acid (ALA) and melatonin were investigated in the female Syrian hamster Harderian gland. This is an organ physiologically exposed to strong oxidative stress due to the highest porphyrinogenic rates known in nature. Enzyme activities of porphyrin biosynthesis and of antioxidative protection, oxidative protein modification, and histological integrity were studied. In the porphyrin biosynthetic pathway, ALA and melatonin acted synergistically by downregulating ALA synthase (ALA-S) and stimulating product formation from ALA; the combination of ALA and melatonin suppressed ALA-S activity, down to about 1% of that in controls. While ALA effects on porphyrinogenesis can be interpreted in terms of homeostasis, melatonin's actions may be seen in relation to seasonality and/or reduction of oxidative stress. Among antioxidant enzymes, superoxide dismutase (SOD) and glutathione reductase (GR) activities were diminished by ALA, presumably due to the vulnerability of their active centers to free radicals, whereas melatonin moderately increased SOD. Both ALA and melatonin strongly stimulated catalase (CAT), thereby counteracting the oxidative stress induced by ALA and its metabolites. Nevertheless, exogenous ALA caused a strong net rise in protein carbonyl and considerable damage of tissue. When given together with ALA, melatonin antagonized these effects and largely protected the integrity of glandular structures.

Effects of the circadian mutation 'tau' on the Harderian glands of Syrian hamsters

The Syrian hamster Harderian gland (HG) is an organ continually exposed to oxidative stress caused by high concentrations of porphyric metabolites. According to previous studies, melatonin, which is rhythmically secreted by the pineal gland and tonically produced by the HG, antagonizes the oxidative damage. HGs exhibit a strong gender-dependent correlation between porphyrins, melatonin, and histological appearance. In HGs of both sexes, we have investigated effects of a single gene defect in the circadian clock system (tau mutation) causing a shortened free-running period and an advanced maximum of circulating melatonin. Comparisons were made with wild-type animals, one group of which received daily pharmacological injections of melatonin in late photophase. Changes were observed in histological characteristics, porphyrin content, antioxidant enzyme activities, and damage of proteins and lipids. HGs of tau hamsters showed morphological changes which can be partially interpreted in terms of increased damage. Additionally, tau females exhibited a many-fold augmentation in the percentage of so-called type II cells, which are otherwise typical for the male glands. In tau hamsters of both sexes, major antioxidative enzyme activities (superoxide dismutase, glutathione reductase, and catalase) were markedly enhanced, a presumably compensatory response to increased oxidative stress. Higher oxidative damage in tau HGs was directly demonstrable by a many-fold increase in protein carbonyl. Rises in antioxidative enzymes were also observed upon injections of melatonin; this was, however, not accompanied by changes in protein carbonyl, so that enzyme inductions by the hormone should be understood as protective actions. Our data are not only in accordance with findings on protective effects by melatonin, but also with our earlier observation made in Drosophila that perturbations in the circadian system lead to increased oxidative stress.

Porphyric enzymes in hamster Harderian gland, a model of damage by porphyrins and their precursors. A chronobiological study on the role of sex differences

The Syrian hamster Harderian gland (HG), representing a highly porphyrogenic organ, was used as a model system for studying physiologically occurring damage of biomolecules by porphyrins and their precursors, phenomena associated with from the pathological situation of porphyrias. The species used exhibits the peculiarity of much higher porphyrogenesis in females than in males, offering possibilities for comparison of effects by different porphyrin levels in one species. Since concentrations of free, and therefore, radical-generating porphyric metabolites are difficult to determine in the presence of high amounts of secreted and crystallizing porphyrins, which are, moreover, mainly surface-reactive, and since indications existed for temporal changes in the oxidative stress caused by these molecules, the following approach was chosen: in HGs of both females and males, activities of the relevant porphyric enzymes, delta-aminolevulinate synthase (ALA-S), delta-aminolevulinate dehydratase (ALA-D) and porphobilinogen deaminase (PBG-D), were determined throughout the circadian cycle. Results were compared with the temporal patterns of lipid peroxidation and protein damage in the same glands. In females, a strong correspondence was observed between protein carbonyl and lipid peroxidation, peaking at the end of both photophase and scotophase; maximal activities of the three porphyric enzymes ALA-S, ALA-D, and PBG-D either coincided or slightly preceded the peaks of oxidative damage. In males, lower enzyme activities, especially in PBG-D, were associated with weakly expressed rhythmicity. Correspondingly, lipid peroxidation was lower and exhibited a smaller rhythm amplitude; protein carbonyl of males showed a temporal pattern differing from that of females, with regard to amplitude and phasing. These data are in agreement with morphological observations demonstrating particularly severe cell damage in the female HG under normal conditions.

Physiological oxidative stress model: Syrian hamster Harderian gland-sex differences in antioxidant enzymes

The Syrian hamster Harderian gland, a juxtaorbital organ exhibiting marked gender-associated differences in contents of porphyrins and melatonin, was used as a model system for comparing strong (in females) and moderate (in males) physiological oxidative stress. Histological differences showing much higher cell damage in females were studied in conjunction with lipid peroxidation and activities of superoxide dismutase, catalase, glutathione peroxidase, and glutathione reductase. Lipid peroxidation and enzyme activities were measured throughout the circadian cycle, revealing the importance of dynamical processes in oxidative stress. Especially in lipid peroxidation and in catalase, short-lasting rises exhibited strongest gender differences. Peaks of lipid peroxidation were about three times higher in females, compared to males. Catalase peaks of females exceeded those in males by several hundred-fold. Average levels of superoxide dismutase and glutathione peroxidase were about three or two times higher in females, respectively. A clear-cut diurnally peaking rhythm was found in glutathione peroxidase of females, which was not apparent in males. Glutathione reductase showed differences in time patterns, but less in average activities. The time courses of lipid peroxidation and of protective enzymes are not explained by circulating melatonin, whereas melatonin formed in the Harderian gland should contribute to differences in average levels. Neither damage nor antioxidative defense simply reflect the illumination cycle and are, therefore, not only a consequence of photoreactions.

Mitochondrial Antisense RNA for Cytochrome C Oxidase (MARCO) Can Induce Morphologic Changes and Cell Death in Human Hematopoietic Cell Lines

To identify essential molecules capable of inducing terminal morphologic maturation and cell death of myeloid progenitor cells, we isolated cDNA clones by functional expression cloning using a library constructed from all-trans retinoic acid (ATRA)-treated human promyelocytic HL-60 cells. Clones which induced morphologic changes in HL-60 cells from blastic cells to mature neutrophilic granulocytes were selected. The isolated positive cDNA clone was demonstrated to encode an antisense RNA for cytochrome c oxidase/serine tRNA derived from a mitochondrial gene (MARCO). When MARCO was expressed in HL-60 cells with the lac switch system, blastic cell morphology became neutrophilic after 48-hour incubation with IPTG, and cell death was observed after 3 days. Also, high molecular weight DNA fragmentation was observed after 36 hours in culture. Similar results were observed using transformants from human K562 cells and CMK cells. RT-PCR analysis revealed that MARCO was transcribed in both ATRA and TNF-α systems, and also in human blood neutrophilic granulocytes. Following transfection with cytochrome c oxidase expression plasmids, TNF-α–induced high molecular weight DNA fragmentation in U937 cells and HL-60 cells was inhibited in these transformants. These results indicate that maturational changes in hematopoietic cells and the process of cell death may be induced by mitochondrial respiratory insufficiency, and also that the mitochondrial gene MARCO may be used as one of the candidates for gene supplementation therapy for the acute leukemias.

Mitochondrial Antisense RNA for Cytochrome C Oxidase (MARCO) Can Induce Morphologic Changes and Cell Death in Human Hematopoietic Cell Lines

To identify essential molecules capable of inducing terminal morphologic maturation and cell death of myeloid progenitor cells, we isolated cDNA clones by functional expression cloning using a library constructed from all-trans retinoic acid (ATRA)-treated human promyelocytic HL-60 cells. Clones which induced morphologic changes in HL-60 cells from blastic cells to mature neutrophilic granulocytes were selected. The isolated positive cDNA clone was demonstrated to encode an antisense RNA for cytochrome c oxidase/serine tRNA derived from a mitochondrial gene (MARCO). When MARCO was expressed in HL-60 cells with the lac switch system, blastic cell morphology became neutrophilic after 48-hour incubation with IPTG, and cell death was observed after 3 days. Also, high molecular weight DNA fragmentation was observed after 36 hours in culture. Similar results were observed using transformants from human K562 cells and CMK cells. RT-PCR analysis revealed that MARCO was transcribed in both ATRA and TNF-α systems, and also in human blood neutrophilic granulocytes. Following transfection with cytochrome c oxidase expression plasmids, TNF-α–induced high molecular weight DNA fragmentation in U937 cells and HL-60 cells was inhibited in these transformants. These results indicate that maturational changes in hematopoietic cells and the process of cell death may be induced by mitochondrial respiratory insufficiency, and also that the mitochondrial gene MARCO may be used as one of the candidates for gene supplementation therapy for the acute leukemias.

Hormonal regulation of FHG22 mRNA in Syrian hamster harderian glands: role of estradiol

The regulation of the FHG22 gene by sex steroids has been studied in Syrian hamster Harderian gland, an organ with sexual dimorphism in which the FHG22 mRNA is female-specific. Testosterone treatment of females caused irregular inhibitory effects on the FHG22 mRNA levels, whereas male castration originated transitory increases during less than 2 weeks. Treatment of 15 day-castrated males for 1 or 2 days with beta-estradiol-3-benzoate caused a marked stimulation in the FHG22 mRNA levels. The results found in vivo may be explained considering those found in female Harderian gland serum-free primary cell cultures. In the absence of hormones, the FHG22 mRNA levels decreased along the time and neither progesterone, testosterone, or 5 alpha-dihydrotestosterone affected the expression. However, estradiol stimulated the FHG22 mRNA expression in a time and dose-dependent manner: increasing effects were detected between 8-96 h of treatment and the EC50 was about 10(-9) M. The estradiol effect was reverted by the antiestrogen ICI 164,384 or by cycloheximide. We conclude that estradiol stimulates FHG22 mRNA expression in Harderian gland, although other agents may also control the expression in vivo.

Invasive processes in the normal Harderian gland of Syrian hamster

In this contribution we will pay special attention to several morphological findings that we can observe, under some circumstances, in the normal Harderian gland of the Syrian hamster. The accumulation of porphyrins in this gland results in mitochondrial damage and extensive cell death. Many damaged cells are secreted into the lumen of the tubule-alveoli, but most of them seem to produce an invasive process that even affects the vascular components of the gland. In this way, many blood vessels are invaded and appear partially filled with the invasive mass, which sometimes totally occludes the lumen of the vessels. We have also observed other surprising features related to a special kind of activity in certain secretory cells. Such activity results in a peculiar "segregation" of a cytoplasmic fragment, containing the nucleus. The affected cells seem to gather up their cytoplasm and nucleus towards the basal zone, while the rest of the cell, including practically the whole amount of lipid droplets, is relegated to the vicinity of the lumen. All these phenomena seem finally to result in the detachment of some clusters, composed of a limited number of cells, which display a basophilic cytoplasm practically free of lipid droplets.

Regulation of the aminolevulinate synthase gene in the Syrian hamster Harderian gland: changes during development and circadian rhythm and role of some hormones

The Syrian hamster Harderian gland has been advocated as a model to study the porphyrin biosynthetic pathway, since it shows by far the highest porphyrin concentration known to date. Another particular characteristic is the sexual dimorphism at both the morphological and the biochemical levels. We found a variation in the ALV-S (aminolevulinate synthase) gene expression according to sex, with females exhibiting much higher mRNA levels than do males. After castration, ALV-S mRNA rose considerably in males, this increase being inhibited by darkness or treatment with melatonin. Treatment with hCG or progesterone did not vary the ALV-S mRNA levels in females. Castrated males, however, showed a much larger increase when they were treated with hCG. No variations have been found in the expression of the ALV-S gene in female HG throughout the estrous cycle. During development, males and females showed similar ALV-S mRNA levels until they were 20 days old. Afterwards, they started showing gender-associated differences. In females, ALV-S mRNA levels rose during the first 3 months of life, and thereafter they decreased progressively with aging. A circadian rhythm has been found in the gene expression of ALV-S mRNA in females, showing very low levels in the morning and reaching a peak during the first hours of darkness. It was an endogenous rhythm, probably regulated at the transcriptional level. It is proposed that the light-dark period duration modulates this rhythm through the suprachiasmatic nucleus which in turn acts on the pineal secretion of melatonin that regulates ALV-S gene expression.

Cell biology of the harderian gland

The harderian gland is an orbital gland of the majority of land vertebrates. It is the only orbital gland in anuran amphibians since the lacrimal gland develops later during phylogenesis in some reptilian species. Perhaps because it is not found in man, little interest was paid to this gland until about four decades ago. In recent years, however, the scientific community has shown new interest in analyzing the ontogenetic and morphofunctional aspects of the harderian gland, particularly in rodents, which are the preferred experimental model for physiologists and pathologists. One of the main characteristics of the gland is the extreme variety not only in its morphology, but also in its biochemical properties. This most likely reflects the versatility of functions related to different adaptations of the species considered. The complexity of the harderian gland is further shown in its control by many exogenous and endogenous factors, which vary from species to species. The information gained so far points to the following functions for the gland: (1) lubrication of the eye and nictitating membrane, (2) a site of immune response, particularly in birds, (3) a source of pheromones, (4) a source of saliva in some chelonians, (5) osmoregulation in some reptiles, (6) photoreception in rodents, (7) thermoregulation in some rodents, and (8) a source of growth factors.

Cloning of a Syrian hamster cDNA related to sexual dimorphism: establishment of a new family of proteins

The clone FHG22, isolated from a female minus male subtracted cDNA library obtained from the sexually dimorphic Syrian hamster Harderian glands (HG) is 440 bp long with a 95 amino acids ORF, and hybridizes to a female HG-specific 0.6 kb mRNA. The FHG22 nucleotide and amino acid sequences are similar to the subunits from prostatein, uteroglobin, major cat allergen Fel dI (chain 1) and mouse salivary androgen binding proteins (subunit alpha). Therefore I propose that all those polypeptides belong to a common new family. The hamster genome has a single copy of the FHG22 gene, without homologous genes. FHG22 mRNA is also found in male and female parotid (higher levels in females) and submandibular glands, indicating a tissue and sex-dependent control of expression.

The pineal neurohormone melatonin prevents in vivo and in vitro apoptosis in thymocytes

Recently, melatonin was found to be the most potent physiological free radical scavenger known to date. In this work, we attempted to define the role this neurohormone plays in the regulation of apoptosis, since the effect of bcl-2, the main gene implicated in its inhibition, acts via an antioxidant mechanism. We investigated the role of melatonin in cell death of thymus, a well known model for the study of apoptosis. Two sets of experiments were carried out: in vivo experiments, performed with Wistar rats, and in vitro experiments, performed with primary cultures of young Wistar rat thymocytes treated with glucocorticoids in order to induce apoptosis. Morphometrical studies in semithin sections of thymus and analysis of DNA fragmentation by gel electrophoresis show that physiological apoptosis occurring in thymus of 65 days old rats, is prevented by the daily administration of melatonin beginning when the rats were 25 days old. Also, we found that at a concentration of 10(-7) M, melatonin decreases by 35% the percentage of apoptotic cells induced by glucocorticoids in cultured thymocytes of 25 day old rats. 10(-9) M melatonin decreases cell death by 20%. Finally, melatonin at 10(-11) M did not have any effect. Several hypothesis are discussed to explain this effect: direct interaction of melatonin with glucocorticoid receptors in the thymus; induction of interleukin-4 release; direct genomic action modulating the expression of apoptosis-inhibiting genes; an effect on nitric oxide synthase; and finally, the antioxidant action of melatonin. Since apoptosis is a possible mechanism involved in neuronal death shown in several neurodegenerative diseases such as Parkinson or Alzheimer's diseases, investigative efforts should be directed to the possible role of melatonin in inhibiting cell death in tissues other that the thymus. Melatonin might be a potent therapeutic agent in some of these conditions.