Effect of hamster pregnancy on female protein, a homolog of serum amyloid P component.

Pentraxins such as human serum amyloid P component (SAP) and C reactive protein (CRP) represent an ancient family of proteins that are ubiquitous in nature and have evolved with little change in structure or regulation. The pentraxin in the Syrian hamster (Mesocricetus auratus) is unique because it is preferentially expressed in the female at high constitutive levels and accordingly called female protein (FP) or FP(SAP) due to its close homology with human SAP. The high levels of FP in female serum (100-fold greater than male serum) suggested its role in hamster pregnancy, one of the shortest of any eutherian mammal. We determined the serum FP concentration in pregnant Syrian hamsters and found a marked decrease (>80%) at term with the nadir at parturition with subsequent increase. A similar downregulation of FP was found in the normal female Syrian hamster after injury (acute phase response), so in both cases the assumed beneficial effects were achieved with less, rather than more pentraxin, a paradoxical pentraxin response. The fall in serum FP concentration could represent a response to protect the fetus from the high and potentially toxic level of FP normally found in the female, that is harmful because of its association with amyloidosis. An FP that is 97.5% identical to Syrian hamster FP is found in the Turkish hamster (Mesocricetus brandti), although serum levels in females are much lower, and amyloid is very rare. During pregnancy/parturition of Turkish hamsters, the serum level of FP remained remarkably constant. In a more distantly related hamster, the Armenian hamster (Cricetulus migratorius), serum FP actually increased during pregnancy and at parturition in a manner similar to that found in the Armenian hamster during an acute phase response. The heterogeneity of FP kinetics during pregnancy in these three species of hamster indicates pleomorphic gene structure for regulation of their similar FPs, and suggests that this protein may have a different function in the pregnancy of each species.     

The role of the female Syrian hamster protein on the interaction between serum lipoproteins and heparin

We have previously shown the effect of phosphorylcholine-binding proteins from rat (PCBP) and rabbit (CRP) on the precipitation of serum lipoproteins by heparin in presence of Ca2+. The present paper describes the effect of a phosphorylcholine-binding protein from the female Syrian hamster (FP) on the lipoprotein precipitation reaction. The precipitation of lipoproteins by heparin was lower in assays using female hamster serum in which FP is a prominent protein, compared with assays with male serum in which FP is present in very low concentration. Depletion of FP from female serum resulted in increased lipoprotein precipitation. The addition of purified FP to assays using human very low density lipoprotein (VLDL) inhibited the precipitation reaction. The precipitation of lipoproteins was also examined using serum from male hamsters treated with diethylstilbestrol and female hamsters treated with testosterone, treatments known to modulate the levels of FP. Results indicate an inverse relationship between serum FP levels from normal and hormone-treated hamsters and the precipitation of lipoproteins from their serum. The partially desialylated FP when added to precipitation assays using human VLDL resulted in reduced inhibition of VLDL precipitation.     

Hamster female protein, a pentameric oligomer capable of reassociation and hybrid formation

Syrian hamster female protein (SFP), a serum oligomer composed of five identical subunits, was reassociated in vitro from monomer subunits. The reconstituted pentamer was genuine by morphologic, antigenic, and structural criteria. Another female protein (FP), a homologue from Armenian hamsters (AFP), also reassociated into a pentamer after dissociation with 5 M guanidine hydrochloride. These two FP's hybridized when a mixture of them was dissociated and then reassociated. Differences between the parent FP's were used to show that the recombinant pentamer contained monomer subunits from both SFP and AFP. Reassociation of both FP's was enhanced by increasing FP concentration and also by adding Ca2+ during reassembly. The two FP's differed in their reassociation profile in that SFP was especially efficient in reassembly, whereas AFP was more dependent upon Ca2+. Female protein is a homologue of C-reactive protein and amyloid P component, and all of these proteins (pentraxins) share a similar structure. The in vitro dissociation-reassociation of female protein described herein may reflect an in vivo dissociation-reassociation which is functionally important and a common metabolic feature within this family of proteins.     

Expression and sequence analyses of serum amyloid A in the Syrian hamster

Reactive amyloidosis occurs during chronic inflammation and involves deposition of amyloid A (AA) fibrils in many organs. Amyloid A is derived by proteolysis from serum amyloid A component (SAA), a major acute-phase reactant in many species. Since spontaneous amyloidosis occurs commonly in Syrian hamsters, we have studied the structure and expression of SAA genes during inflammation in these animals. Two cDNA clones and one genomic clone were sequenced, suggesting that Syrian hamster SAA is encoded by at least two genes. Hepatic mRNA analyses showed that SAA was inducible in many hamster organs during acute inflammation. These studies also demonstrated that SAA mRNA for one isotype is maximally expressed at a site of local tissue damage.     

Effects of human chorionic gonadotropin and progesterone administration on porphyrin biosynthesis and histology of the Harderian glands in male and female Syrian hamsters.

We investigated the influence of hCG and progesterone on the control of porphyrin biosynthesis and histology in the Syrian hamster Harderian glands. Castration of male hamsters caused a marked elevation in porphyrin biosynthesis as revealed by the concentrations of porphyrins and the mRNA levels of the porphyrin pathway rate-limiting enzyme, 5-aminolevulinate synthase (ALV-S). Injection of hCG into castrated male hamsters also resulted in a significant increase in both porphyrin concentrations and levels of ALV-S mRNA compared with those in saline-injected castrated hamsters. Type II cells, which are filled with large lipid vacuoles and are characteristic of male phenotype, disappeared after castration, but administration of hCG partially prevented this change. On the other hand, neither administration of hCG nor progesterone implants could increase the very high porphyrin concentrations and ALV-S mRNA levels characteristic of female Syrian hamsters. As in the case of castrated male hamsters, injections of 20 IU hCG to female Syrian hamsters increased the relative number of Type II cells per square millimeter, whereas progesterone administration did not modify the relative number of Type II cells. These results indicate that hCG can modify Harderian gland morphology in both male and female hamsters and can exert a positive control in the expression of ALV-S gene in castrated male hamsters.     

Species differences in hepatic peroxisome proliferation, cell replication and transforming growth factor-beta1 gene expression in the rat, Syrian hamster and guinea pig

The objective of this study was to evaluate species differences in the hepatic effects of three potent rodent peroxisome proliferators, namely methylclofenapate (MCP), ciprofibrate (CIP) and Wy-14,643 (WY), particularly with respect to effects on replicative DNA synthesis and transforming growth factor-beta1 (TGF-beta1) gene expression. Male Sprague-Dawley rats, Syrian hamsters and Dunkin-Hartley guinea pigs were given daily oral doses of 0 (corn oil) and 75 mg/kg MCP for periods of 6 and 21 days. Syrian hamsters and guinea pigs were also treated with 25 mg/kg CIP and 25 mg/kg WY. Relative liver weights were significantly increased in peroxisome proliferator-treated rats and Syrian hamsters, but not in guinea pigs. Hepatic peroxisomal (palmitoyl-CoA oxidation) and microsomal (lauric acid 12-hydroxylase) fatty acid oxidising enzyme activities and CYP4A isoform mRNA levels were significantly increased in rats and Syrian hamsters, whereas only minor effects were observed in the guinea pig. Replicative DNA synthesis was studied by implanting 7-day osmotic pumps containing 5-bromo-2'-deoxyuridine during study days -1 to 6 and 14 to 21. Hepatocyte labelling index values were increased by MCP in the rat, but neither MCP, CIP nor WY produced any significant effect on replicative DNA synthesis in the Syrian hamster and guinea pig. MCP treatment increased TGF-beta1 and insulin-like growth factor II/mannose-6-phosphate (IGFII/Man6P) receptor gene expression in the rat. In the Syrian hamster, effects on TGF-beta1 and IGFII/Man6P receptor gene expression were also observed in some instances, whereas TGF-beta1 mRNA levels were essentially unchanged in the guinea pig. These results provide further evidence for marked species differences in response to rodent peroxisome proliferators. While peroxisome proliferators produce a wide spectrum of effects in rat liver, other species such as the Syrian hamster and guinea pig are less responsive and in the case of some endpoints (e.g., cell replication) may be refractory.     

Development and androgen regulation of the secretory cell types of the Syrian hamster (Mesocricetus auratus) Harderian gland

The secretory cell types of the hamster Harderian glands were studied in both male and female Syrian hamsters. As previously demonstrated, female hamsters showed a single secretory cell type (type I), while male hamsters displayed two secretory cell types (type I and type II). Type-II cells were observed after the first month of age correlating with the increase in testosterone levels. The administration of testosterone to adult female hamsters resulted in a marked increase in the percentage of type-II cells without a significant increase in the number of mitotic figures. Very low levels of serum testosterone were able to maintain the percentage of type-II cells. Castration of male hamsters produced a decrease in the percentage of type-II cells. This drop correlated with the reduction in serum testosterone levels. The chronic administration of a luteinizing hormone-releasing hormone agonist to male Syrian hamsters induced a significant reduction in both serum luteinizing hormone and testosterone. However, the percentage of type-II cells was similar to that of control hamsters suggesting that very low levels of circulating testosterone are able to maintain the percentage of type-II cells. In a final experiment male Syrian hamsters were treated with the antiadrogen cyproterone acetate. No changes were observed in the percentage of type-II cells, whereas serum luteinizing hormone and testosterone levels were significantly modified. We concluded that (1) type-II cells differentiate from type-I cells; (2) gonadal androgens are the major factor controlling this differentiation; and (3) the disappearance of type-II cells after androgen deprivation occurs through holocrine and apocrine mechanisms. The possible implication of 5-reductase in the regulation of secretory cell types in the Harderian glands of hamsters is discussed.     

Changes in expression of serine proteases HtrA1 and HtrA2 during estrogen-induced oxidative stress and nephrocarcinogenesis in male Syrian hamster

Serine proteases HtrA1 and HtrA2 are involved in cellular stress response and development of several diseases, including cancer. Our aim was to examine the involvement of the HtrA proteins in acute oxidative stress response induced in hamster kidney by estrogen treatment, and in nephrocarcinogenesis caused by prolonged estrogenization of male Syrian hamster. We used semi-quantitative RT-PCR to estimate the HtrA1 and HtrA2 mRNA levels in kidney tissues, and Western blotting to monitor the amount of the HtrA proteins. Within the first five hours following estrogen administration both HtrA1 mRNA and the protein levels were increased significantly. No changes in the expression of HtrA2 were observed. This indicates that HtrA1 may be involved in the response against oxidative stress induced by estrogen treatment in hamster kidney. During prolonged estrogenization, a significant reduction of the HtrA1 mRNA and protein levels was observed after 6 months of estradiol treatment, while the expression of HtrA2 was significantly elevated starting from the third month. This suggests an involvement of the HtrA proteins in estrogen-induced nephrocarcinogenesis in hamster. Using fluorescence in situ hybridization we localized the HtrA1 gene at the qb3-4 region of Syrian hamster chromosome 2, the region known to undergo a nonrandom deletion upon prolonged estrogenization. It is possible that the reduced level of HtrA1 expression is due to this chromosomal aberration. A full-length cDNA sequence of the hamster HtrA1 gene was obtained. It codes for a 50 kDa protein which has 98 and 96% identity with mouse and human counterparts, respectively.     

Increased expression of the gene for alpha-interferon-inducible protein in cardiomyopathic hamster heart

Cardiomyopathic (CM) hamsters have a disruption in the delta-sarcoglycan gene which leads to progressive cardiac necrosis by 30 to 40 days of age, hypertrophy by 120 days, and heart failure by 250 days. We used differential display to detect other changes in mRNA levels in 30-, 60-, and 90-day-old wild-type and CM hamsters. We identified a 400-bp cDNA with sequence similarity to the human alpha-interferon-inducible protein (p27). This cDNA annealed with a 570-base mRNA whose steady-state levels were increased in 30-, 60-, and 90-day-old CM compared to wild-type heart. Increased expression of this hamster homolog of p27 (p27-h) was detected in CM hamster cardiac and skeletal muscle at 60 days of age but not in liver, kidney, or brain. Thus, an inherited defect in CM hamsters leads to increased expression of p27-h in advance of the development of hypertrophy and heart failure.     

Three hamster species with different scrapie incubation times and neuropathological features encode distinct prion proteins.

Given the critical role of the prion protein (PrP) in the transmission and pathogenesis of experimental scrapie, we investigated the PrP gene and its protein products in three hamster species, Chinese (CHa), Armenian (AHa), and Syrian (SHa), each of which were found to have distinctive scrapie incubation times. Passaging studies demonstrated that the host species, and not the source of scrapie prions, determined the incubation time for each species, and histochemical studies of hamsters with clinical signs of scrapie revealed characteristic patterns of neuropathology. Northern (RNA) analysis showed the size of PrP mRNA from CHa, AHa, and SHa hamsters to be 2.5, 2.4, and 2.1 kilobases, respectively. Immunoblotting demonstrated that the PrP isoforms were of similar size (33 to 35 kilodaltons); however, the monoclonal antibody 13A5 raised against SHa PrP did not react with the CHa or AHa PrP molecules. Comparison of the three predicted amino acid sequences revealed that each is distinct. Furthermore, differences within the PrP open reading frame that uniquely distinguish the three hamster species are within a hydrophilic segment of 11 amino acids that includes polymorphisms linked to scrapie incubation times in inbred mice and an inherited prion disease of humans. Single polymorphisms in this region correlate with the presence or absence of amyloid plaques for a given hamster species or mouse inbred strain. Our findings demonstrate distinctive molecular, pathological, and clinical characteristics of scrapie in three related species and are consistent with the hypothesis that molecular properties of the host PrP play a pivotal role in determining the incubation time and neuropathological features of scrapie.     

Asymmetric learning to avoid heterospecific males in Mesocricetus hamsters

If a female mates with a male of a closely related species, her fitness is likely to decline. Consequently, females may develop behavioral mechanisms to avoid mating with heterospecific males. In some species, one such mechanism is for adult females to learn to discriminate against heterospecific males after exposure to such males. We have previously shown that adult, female Syrian hamsters (Mesocricetus auratus) learn to discriminate against male Turkish hamsters (Mesocricetus brandti) after exposure to a single heterospecific male during 8 days across a wire-mesh barrier. Here we repeated that experiment but this time we exposed female Turkish hamsters to a male Syrian hamster for 8 days and then measured sexual and aggressive behaviors towards that heterospecific male and towards a conspecific male. In contrast to female Syrian hamsters, female Turkish hamsters did not differ in their latency to go into lordosis or in any measure of aggression towards either type of male. Female Turkish hamsters spent less time in lordosis with the heterospecific male, but the percentage of trials in which females copulated with conspecific and heterospecific males did not differ. When comparing females from both species that had been exposed to a heterospecific male for 8days, female Syrian hamsters copulated less and were more aggressive towards the heterospecific male compared to the behavior of female Turkish hamsters. We discuss how this asymmetric response between females of the two species may be due to the much larger geographical range of Turkish hamsters compared to Syrian hamsters.     

Ovariectomized hamster: a potential model of postmenopausal hypercholesterolemia

A suitable and economical animal model of ovarian hormone deficiency can greatly enhance the understanding of postmenopausal-elevated risk of coronary heart disease. The male Golden Syrian hamster is a well-established small animal model of hypercholesterolemia, but the effect of ovariectomy on lipid profile in the female hamster is unclear. The objective of this study was to determine whether ovariectomized hamsters develop hypercholesterolemia and experience changes in body fat distribution consistent with changes observed in postmenopausal women. Twenty-two 90-day-old female Golden Syrian hamsters were divided into two groups and were either ovariectomized or sham-operated and given free access to a standard cholesterol-free laboratory diet for 65 days. Ovariectomized hamsters had significantly (P < 0.05) elevated serum total cholesterol concentrations (16.6%) as well as abdominal fat mass (56%; P< 0.01) despite equal food intake compared with the sham-operated group. In contrast, the mean intestinal weight and in vivo rate of sterol biosynthesis were significantly (P < 0.002 and P = 0.01, respectively) lower in the ovariectomized compared with the sham-operated group. In vivo rates of hepatic sterol biosynthesis were directionally lower (P = 0.1) in the ovariectomized group. No significant differences were observed in final body weight, serum triglycerides, or liver total cholesterol and lipids between the two groups. In conclusion, ovariectomized hamsters undergo changes in serum cholesterol and fat distribution similar to those experienced by postmenopausal women, and thus may serve as an appropriate model for postmenopausal hypercholesterolemia.     

Transmission and adaptation of chronic wasting disease to hamsters and transgenic mice: evidence for strains

In vitro screening using the cell-free prion protein conversion system indicated that certain rodents may be susceptible to chronic wasting disease (CWD). Therefore, CWD isolates from mule deer, white-tailed deer, and elk were inoculated intracerebrally into various rodent species to assess the rodents' susceptibility and to develop new rodent models of CWD. The species inoculated were Syrian golden, Djungarian, Chinese, Siberian, and Armenian hamsters, transgenic mice expressing the Syrian golden hamster prion protein, and RML Swiss and C57BL10 wild-type mice. The transgenic mice and the Syrian golden, Chinese, Siberian, and Armenian hamsters had limited susceptibility to certain of the CWD inocula, as evidenced by incomplete attack rates and long incubation periods. For serial passages of CWD isolates in Syrian golden hamsters, incubation periods rapidly stabilized, with isolates having either short (85 to 89 days) or long (408 to 544 days) mean incubation periods and distinct neuropathological patterns. In contrast, wild-type mouse strains and Djungarian hamsters were not susceptible to CWD. These results show that CWD can be transmitted and adapted to some species of rodents and suggest that the cervid-derived CWD inocula may have contained or diverged into at least two distinct transmissible spongiform encephalopathy strains.     

Ezetimibe ameliorates intestinal chylomicron overproduction and improves glucose tolerance in a diet-induced hamster model of insulin resistance

Ezetimibe is a cholesterol uptake inhibitor that targets the Niemann-Pick C1-like 1 cholesterol transporter. Ezetimibe treatment has been shown to cause significant decreases in plasma cholesterol levels in patients with hypercholesterolemia and familial hypercholesterolemia. A recent study in humans has shown that ezetimibe can decrease the release of atherogenic postprandial intestinal lipoproteins. In the present study, we evaluated the mechanisms by which ezetimibe treatment can lower postprandial apoB48-containing chylomicron particles, using a hyperlipidemic and insulin-resistant hamster model fed a diet rich in fructose and fat (the FF diet) and fructose, fat, and cholesterol (the FFC diet). Male Syrian Golden hamsters were fed either chow or the FF or FFC diet ± ezetimibe for 2 wk. After 2 wk, chylomicron production was assessed following intravenous triton infusion. Tissues were then collected and analyzed for protein and mRNA content. FFC-fed hamsters treated with ezetimibe showed improved glucose tolerance, decreased fasting insulin levels, and markedly reduced circulating levels of TG and cholesterol in both the LDL and VLDL fractions. Examination of triglyceride (TG)-rich lipoprotein (TRL) fractions showed that ezetimibe treatment reduced postprandial cholesterol content in TRL lipoproteins as well as reducing apoB48 content. Although ezetimibe did not decrease TRL-TG levels in FFC hamsters, ezetimibe treatment in FF hamsters resulted in decreases in TRL-TG. Jejunal apoB48 protein expression was lower in ezetimibe-treated hamsters. Reductions in jejunal protein levels of scavenger receptor type B-1 (SRB-1) and fatty acid transport protein 4 were also observed. In addition, ezetimibe-treated hamsters showed significantly lower jejunal mRNA expression of a number of genes involved in lipid synthesis and transport, including srebp-1c, sr-b1, ppar-γ, and abcg1. These data suggest that treatment with ezetimibe not only inhibits cholesterol uptake, but may also alter intestinal function to promote improved handling of dietary lipids and reduced chylomicron production. These, in turn, promote decreases in fasting and postprandial lipid levels and improvements in glucose homeostasis.     

Circadian clock speed increases during aging in the male Syrian hamster: A large-scale study

There are conflicting reports in the literature as to whether or not the circadian period in Syrian hamsters shortens with age, and those studies were conducted with small sample sizes. This report mines data from a large number of experiments resulting in more than 1000 measurements of circadian period in hamsters during aging up to 6 months, and this was correlated with both age and weight. Circadian period was calculated while hamsters were in running wheels in constant darkness. There is a weak correlation between hamster weight and circadian period, and there is significant shortening of circadian period during aging.     

Immunohistochemical renin study of DES-induced renal tumor in the Syrian hamster

Diethylstilbestrol (DES) treatment of a male Syrian hamster resulted in the development of a renal tumor and its widely scattered serosal metastases. Cells in both the primary tumor and metastatic nodules contained secretory granules. The tumors were transplanted serially into DES-supported and non-DES-supported host hamsters until DES-independent tumors developed. Rabbit antiserum to mouse salivary renin and rabbit antiserum to rat kidney resin were reacted with sections of the primary tumor, metastatic nodules, and all transport tumors. The sections were stained by the PAP and Vector-ABC-AP procedures. Renin-positive material was observed in all tumors. Plasma renin activity (PRA) was determined for the host hamsters carrying the renal tumor transplants and compared to the PRA values that had been determined for normal non-DES-treated male and female hamsters. It was found that the average PRA values of host hamsters carrying the tumor transplants were significantly higher than the normal PRA values.     

Effect of RFRP-3 on reproduction is sex- and developmental status-dependent in the striped hamster (Cricetulus barabensis)

RFamide-related peptides (RFRPs) are orthologous to gonadotropin-inhibitory hormone (GnIH) inhibiting gonadotropin release. There are only two RFRP sequences (RFRP-1 and RFRP-3) encoded in rodents. RFRP-3, which was considered as a hypothetical inhibitor on GnRH, shows a stimulatory effect on the male Syrian and male Siberian hamster in short days. As a dominant rodent pest in northern China farmland, the striped hamster (Cricetulus barabensis) has higher reproductive activities and could act as a model to study the mechanism of reproduction. However, the effect of RFRP-3 on the reproductive activity for the striped hamster is less understood. In the study, we cloned 643 bp RFRP cDNA from the striped hamster hypothalamus, which contained an ORF of 570 bp encoding two RFamide-related peptide (RFRP) sequences: SPAPANKVPHSAANLPLRF-NH₂ (C. barabensis RFRP-1) and TLSRVPSLPQRF-NH₂ (C. barabensis RFRP-3). We also investigated the expression variation of RFRP mRNA and GnRH mRNA in the hypothalamus from hamsters with different developmental statuses (7-week-, 13-week- and 1.5-year-olds) using FQ-PCR, in which the 13-week-old female individuals were in estrous. The striped hamsters that are 7 weeks and 1.5 years old are non-breeding individuals, and those that are 13-week hamsters have breeding phenomena. The highest hypothalamus RFRP mRNA level was found in breeding males as compared to non-breeding males. Conversely, the lowest RFRP mRNA level in the hypothalamus was observed in breeding females, with no significant level when the breeding females were compared to the 7-week-old individuals. Additionally, the investigation of GnRH expression level showed a declining expression trend across the developmental stages (7-week-, 13-week- and 1.5-year-olds) in both sexes. Significant negative and positive relationships were detected in the 13-week estrous female (r = − 0.997, P = 0.035) and the 13-week male (r = 0.998, P = 0.029) striped hamsters respectively, which suggest that RFRP-3 has inhibitory and stimulatory effects on female and male adults respectively. Our results suggest that the effects of RFRP-3 on reproduction are sex- and developmental status-dependent in the striped hamster.