Gender-associated differences in the development of 5-aminolevulinate synthase gene expression in the harderian gland of Syrian hamsters

Autophagic and proteolytic processes in the Harderian gland are modulated during the estrous cycle

The Syrian hamster Harderian gland (HG) is an organ that undergoes physiological autophagy in response to oxidative stress induced by porphyrin production. Porphyrin production in the HG has marked sex differences and is closely linked to reproductive function. In the present study, we observed that the estrous cycle and associated estrogen variations may affect oxidative-stress-induced proteolytic processes. In particular, significant changes in autophagic activity were detected during the estrous cycle. Notably, increased activation of macroautophagy as well as chaperone-mediated autophagy in the estrus phase coincided with a minimal antioxidant capability and the highest protein damage levels. By contrast, autophagic machinery was found to be blocked in the diestrus phase, likely due to mammalian target of rapamycin activation, which could be corroborated by the subsequent pS6K activation. Analogous results were observed regarding proteasome activity, which also showed maximal activity in the estrus phase. Interestingly, all these mechanisms were associated with important morphological changes in the HG during the estrous cycle. We observed statistically significant increases in Type II cells, which may be related to extensive autophagy in the estrus phase. Physiologically, this would result in a significant release of porphyrins specifically when females are more receptive. These data support the role of porphyrins as pheromones, as other authors have previously suggested, thus making the HG a scent organ. In addition, these results suggest a porphyrin-based approach to the treatment of porphyria during pregnancy, a condition for which no treatment is currently known.

Effect of estradiol on heme biosynthetic pathway in lead-poisoned rabbits

OBJECTIVES

To clarify the effect of the female hormone estradiol (Est) on heme biosynthesis in lead-poisoned rabbits, parameters indicating lead exposure, such as free erythrocyte protoporphyrin (FEP) level and δ-aminolevulinic acid dehydratase (ALA-D) activity, were determined.

METHODS

Twenty-six male Japanese white rabbits (body weight (BW), 3kg) were divided into four groups: I (control), II (Est), III (Pb), IV (Est+Pb). About 3 weeks after castration, Est (3 mg/kg of BW) was injected intramuscularly, and 2 weeks thereafter, lead (1.2 mg/kg of BW) was injected intravenously. After the initial injection of each of these substances, the same dose of each of these substances was injected once a week until the 9th week.

RESULTS

In groups III and IV, FEP level increased and ALA-D activity in the erythrocytes, bone marrow and liver decreased with an increase in lead concentration in blood. FEP level decreased significantly (p<0.01) in the 8th and 10th weeks after Est injection in group IV compared to with that in group III and was not elevated in group II compared with that in group I. ALA-D activity in the erythrocytes, bone marrow and liver increased significantly in group II compared with that in group I, whereas Ht and Hb levels decreased in group II compared with those in group I, and decreased in group IV compared with those in group III. The level of iron in plasma (Fe-P) was within the normal range during experiment.

CONCLUSIONS

In this study, Est did not increase FEP level. From the above results regarding FEP level and ALA-D activity, Est may prevent an increase in FEP level caused by lead. Ht and Hb levels, which are the parameters of anemia, decreased mainly as a result of Est exposure rather than lead exposure.

Sex differences in expression and differential regulation by androgen and estrogen of two odorant-binding tear lipocalins in lacrimal glands of immature hamsters

In adults of several mammalian species, lacrimal glands (LG) have sex differences but there is no report of any sexual dimorphism in LG of immatures. In LG and tears of adult hamsters, we found female-specific expression of two closely related odorant-/pheromone-binding lipocalins, FLP (female lacrimal protein) and MSP (male-specific protein; initially identified in salivary glands of males). Although, both androgens and estrogens markedly repress FLP and MSP in LG of adults, the expression of these lipocalins in females is due to their incomplete repression by endogenous estrogens. Here we report a marked sexual dimorphism in the expression of FLP and MSP in LG and tears of 20-day-old immature hamsters. The age-dependant expression of these lipocalins and effect of neonatal-gonadectomy and sex hormone treatments on their expression in immatures was investigated. FLP and MSP are detectable in LG at 10-day age in both sexes of hamster but by 20-day age levels of both lipocalins show sex differences wherein FLP is several fold higher in males and MSP is obliterated in males. Thereafter, FLP declines in male LG and is obliterated by 36-day age, resulting in female-specific expression of both LG lipocalins as seen in adults. In LG of 20-day-old immatures, FLP and MSP are insensitive to repression by androgen and estrogen, respectively, which was unlike the androgen/estrogen-repressed regulation of both lipocalins in adult LG. The estrogenic repression of FLP and androgenic repression of MSP in LG of immature hamsters could be prevented by treatment with tamoxifen and flutamide, respectively. Our studies indicate that (i) presence of gonads in immatures can have significant effects on LG lipocalins resulting in their sexually dimorphic expression, (ii) in immatures, unlike adults, the repressive effects of estrogen and androgen on LG lipocalins are selective for FLP and MSP, respectively, and (iii) these repressions are likely to be mediated by sex hormone receptors.

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.

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.

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

BACKGROUND

The Harderian glands of female Syrian hamsters contain very high concentrations of protoporphyrin (in the range of micrograms per mg of tissue) which accumulate in the tubulo-alveoli of the gland. We have studied the process of synthesis, accumulation, and secretion of this cyclic compound by the secretory cells of the hamster Harderian glands.

METHODS

The animals used were female Syrian hamster of 15, 35, 75, 180, and 360 days of age. Items first examined were (1) percentage of the "clear cells," (2) area occupied by intraluminal porphyrins, and (3) histological characteristics of "clear cells" by light and transmission electron microscopy (TEM). In a second study the total content of porphyrins was determined. Finally, the levels of mRNA for the enzyme aminolevulinate synthase (ALV-S) were measured.

RESULTS

In the glands of female hamsters, both the tissue concentration and the intraluminal area occupied by protoporphyrin correlate with the appearance of a special type of cell (clear cells) which show signs of cell degeneration. In addition, the expression of the gene for ALV-S, which is the limiting enzyme in porphyrin production, also parallels the relative number of clear cells. Analyzed under TEM, these clear cells display dilated mitochondria and short and swollen endoplasmic reticulum cisternae. In a late phase of necrosis, the nuclear envelope appears disorganized with scarce chromatin. The mitochondria undergo complete destruction, resulting in electron-dense bacillary formations which progressively coalesce in large and dense areas of protoporphyrin. The cell dies after this accumulation, being secreted by a "cytogen" mechanism.

CONCLUSIONS

In view of our results, the Harderian gland of female Syrian hamster may provide a useful model for the study of the mechanism by which the anomalous accumulation of protoporphyrin induces cell damage in human protoporphyria.

Photoperiod and the pineal gland regulate the male phenotype of the Harderian glands of male Syrian hamsters after androgen withdrawal

The Harderian glands of Syrian hamsters exhibit a marked sexual dimorphism in cell types and porphyrin production. The glands of male hamsters have two secretory cell types (Type I and II) while the glands of females consist of a single secretory cell type (female Type I) and large intraluminal deposits of porphyrins. Besides androgens, there is evidence that the pineal gland, through the secretion of melatonin, contributes to the maintenance of the "male" and "female" phenotypes. In this study, we investigated the effects of castration, short photoperiods, and pinealectomy on the distribution of secretory cells and porphyrin deposits in the Harderian glands of male Syrian hamsters. Two groups of animals were maintained in long days (14 hr light/day). Hamsters in one group were left intact and those in the other were castrated. Another three groups were maintained in short days (8 hr light/day); these animals were either left intact, castrated, or both castrated and pinealectomized. The duration of the experiment was 5 weeks. Castration of long photoperiod-exposed animals resulted in a significant drop in the number of Type II cells and a large increase in the porphyrin deposits (P < 0.01). However, castrated animals exposed to short photoperiod showed a significant smaller change in both parameters compared with those exposed to long days (P < 0.05). Pinealectomy prevented the effects of short days in castrated animals. No significant changes were observed in the relative number of mitotic figures or in the number of cell nuclei, indicating that the changes observed were due in part to a transformation of Type II into Type I cells. In a second experiment, male hamsters were injected daily either with 25 micrograms of melatonin late in the afternoon or with the saline for 8 weeks. The administration of melatonin resulted in a significant (P < 0.05) increase in the percentage of Type II cells. We conclude that when circulating androgens are very low or absent, pineal melatonin maintains the male phenotype in the Syrian hamster Harderian gland.