Field evidence for a proximate role of food shortage in the regulation of hibernation and daily torpor: a review

Hibernation and daily torpor (heterothermy) have long been assumed to be adaptive responses to seasonal energy shortage. Laboratory studies have demonstrated that food shortage alone can trigger the use of heterothermy. However, their potential to predict heterothermic responses in the wild is limited, and few field studies demonstrate the dependence of heterothermy on food availability under natural conditions. Thus, the view of heterothermy as an energy saving strategy to compensate for food shortage largely remains an untested hypothesis. In this paper, we review published evidence on the proximate role of food availability in heterothermy regulation by endotherms, and emphasize alternative hypotheses that remain to be tested. Most studies have relied on correlative evidence. Manipulations of food availability, that demonstrate the proximate role of food availability, have been conducted in only five free-ranging heterotherms. Several other metabolic constraints covary with food availability and can confound its effect. Shortage in water availability, the nutritional composition of food, or subsequent conversion of food in fat storage all could be actual proximate drivers of heterothermy regulation, rather than food shortage. Social interactions, competition for food and predation also likely modulate the relative strength of food shortage between individuals. The ecological relevance of the dependence of heterothermy on food availability remains to be assessed in field experiments that account for the confounding effects of covarying environmental and internal factors.     

Clinical Significance of the CCR5delta32 Allele in Hepatitis C

Background

The CCR5 receptor, expressed on Th1 cells, may influence clinical outcomes of HCV infection. We explored a possible link between a CCR5 32-base deletion (CCR5delta32), resulting in the expression of a non-functioning receptor, and clinical outcomes of HCV infection.

Methods

CCR5 and HCV-related phenotypes were analysed in 1,290 chronically infected patients and 160 patients with spontaneous clearance.

Results

Carriage of the CCR5delta32 allele was observed in 11% of spontaneous clearers compared to 17% of chronically infected patients (OR = 0.59, 95% CI interval 0.35–0.99, P = 0.047). Carriage of this allele also tended to be observed more frequently among patients with liver inflammation (19%) compared to those without inflammation (15%, OR = 1.38, 95% CI interval 0.99–1.95, P = 0.06). The CCR5delta32 was not associated with sustained virological response (P = 0.6), fibrosis stage (P = 0.8), or fibrosis progression rate (P = 0.4).

Conclusions

The CCR5delta32 allele appears to be associated with a decreased rate of spontaneous HCV eradication, but not with hepatitis progression or response to antiviral therapy.     

Reproductive resilience to food shortage in a small heterothermic primate

The massive energetic costs entailed by reproduction in most mammalian females may increase the vulnerability of reproductive success to food shortage. Unexpected events of unfavorable climatic conditions are expected to rise in frequency and intensity as climate changes. The extent to which physiological flexibility allows organisms to maintain reproductive output constant despite energetic bottlenecks has been poorly investigated. In mammals, reproductive resilience is predicted to be maximal during early stages of reproduction, due to the moderate energetic costs of ovulation and gestation relative to lactation. We experimentally tested the consequences of chronic-moderate and short-acute food shortages on the reproductive output of a small seasonally breeding primate, the grey mouse lemur (Microcebus murinus) under thermo-neutral conditions. These two food treatments were respectively designed to simulate the energetic constraints imposed by a lean year (40% caloric restriction over eight months) or by a sudden, severe climatic event occurring shortly before reproduction (80% caloric restriction over a month). Grey mouse lemurs evolved under the harsh, unpredictable climate of the dry forest of Madagascar and should thus display great potential for physiological adjustments to energetic bottlenecks. We assessed the resilience of the early stages of reproduction (mating success, fertility, and gestation) to these contrasted food treatments, and on the later stages (lactation and offspring growth) in response to the chronic food shortage only. Food deprived mouse lemurs managed to maintain constant most reproductive parameters, including oestrus timing, estrogenization level at oestrus, mating success, litter size, and litter mass as well as their overall number of surviving offspring at weaning. However, offspring growth was delayed in food restricted mothers. These results suggest that heterothermic, fattening-prone mammals display important reproductive resilience to energetic bottlenecks. More generally, species living in variable and unpredictable habitats may have evolved a flexible reproductive physiology that helps buffer environmental fluctuations.     

A role for fibroblasts in mediating the effects of tobacco-induced epithelial cell growth and invasion

Cigarette smoke and smokeless tobacco extracts contain multiple carcinogenic compounds, but little is known about the mechanisms by which tumors develop and progress upon chronic exposure to carcinogens such as those present in tobacco products. Here, we examine the effects of smokeless tobacco extracts on human oral fibroblasts. We show that smokeless tobacco extracts elevated the levels of intracellular reactive oxygen, oxidative DNA damage, and DNA double-strand breaks in a dose-dependent manner. Extended exposure to extracts induced fibroblasts to undergo a senescence-like growth arrest, with striking accompanying changes in the secretory phenotype. Using cocultures of smokeless tobacco extracts-exposed fibroblasts and immortalized but nontumorigenic keratinocytes, we further show that factors secreted by extracts-modified fibroblasts increase the proliferation and invasiveness of partially transformed epithelial cells, but not their normal counterparts. In addition, smokeless tobacco extracts-exposed fibroblasts caused partially transformed keratinocytes to lose the expression of E-cadherin and ZO-1, as well as involucrin, changes that are indicative of compromised epithelial function and commonly associated with malignant progression. Together, our results suggest that fibroblasts may contribute to tumorigenesis indirectly by increasing epithelial cell aggressiveness. Thus, tobacco may not only initiate mutagenic changes in epithelial cells but also promote the growth and invasion of mutant cells by creating a procarcinogenic stromal environment.     

Patterns of angiogenic and hematopoietic gene expression during brown trout embryogenesis

In this article, whole mount in situ hybridization is used to examine early blood vessel and blood cell development in the embryos of the brown trout Salmo trutta lacustris. cDNAs encoding for the angiogenic markers fli1 and flk1, and for the hematopoietic markers gata1 and gata2, were identified from an expressed sequence tag library of rainbow trout. Results show that fli1, flk1 and gata2 are activated in bilateral bands of the lateral trunk mesoderm before the onset of somitogenesis, shortly followed by gata1. These bands then converge toward the ventral midline to form the intermediate cell mass (ICM) (anterior ICM). Subsequent axial vasculogenesis and initial blood cell formation involve a clear spatial separation of fli1 and gata gene expression. Fli1 staining is most intense within the axial vessel (dorsal aorta, posterior cardinal vein) forming and lateral ICM cells, whereas binding of gata1 and gata2 probes becomes confined to the central portion of ICM cells beneath the dorsal aorta. This is followed by a first wave of angiogenesis, indicated by expression of fli1 and flk1. This gives rise to the intersegmental, dorsal longitudinal anastomotic and intestinal vessels. Further angiogenesis and hematopoiesis are activated in the "posterior ICM" of the tail. Here, the absence of gata1 indicates that hematopoiesis in this tissue generates myeloid rather than erythroid cells. The results supplement and validate previous, now historical morphological work in salmonids, thus aiding the elucidation of a comprehensive general scheme of angiogenic and hematopoietic development in the teleost embryo.     

Long term regulation of aquaporin-2 expression in vasopressin-responsive renal collecting duct principal cells.

Fine regulation of water reabsorption by the antidiuretic hormone [8-arginine]vasopressin (AVP) occurs in principal cells of the collecting duct and is largely dependent on regulation of the aquaporin-2 (AQP2) water channel. AVP-inducible long term AQP2 expression was investigated in immortalized mouse cortical collecting duct principal cells. Combined RNase protection assay, Western blot, and immunofluorescence analyses revealed that physiological concentrations of AVP added to the basal side, but not to the apical side, of cells grown on filters induced both AQP2 mRNA and apical protein expression. The stimulatory effect of AVP on AQP2 expression followed a V(2) receptor-dependent pathway because [deamino-8-d-arginine]vasopressin (dDAVP), a specific V(2) receptor agonist, produced the same effect as AVP, whereas the V(2) antagonist SR121463B antagonized action of both AVP and dDAVP. Moreover, forskolin and cyclic 8-bromo-AMP fully reproduced the effects of AVP on AQP2 expression. Analysis of protein degradation pathways showed that inhibition of proteasomal activity prevented synthesis of AVP-inducible AQP2 mRNA and protein. Once synthesized, AQP2 protein was quickly degraded, a process that involves both the proteasomal and lysosomal pathways. This is the first study that delineates induction and degradation mechanisms of AQP2 endogenously expressed by a renal collecting duct principal cell line.     

Raman study of potential "antisense" drugs: nonamer oligonucleotide duplexes with a central mismatch as a model system for the binding selectivity evaluation

A set of four 9-mer oligonucleotide duplexes formed between the 5'-GCATNTCAC-3', N=A,C,T,G, and the 5'-GTGATATGC-3' complement has been proposed as a model system for the investigation of novel oligonucleotide analogues (candidates for antisense use) binding selectivity. Raman measurements were carried out on a set of natural DNA 9-mer in order to verify suitability of the model and to obtain reference spectral data. Difference Raman spectra between the mismatch and match duplexes obtained at 15 degrees C exhibited numerous spectral features sensitively indicating the structural changes. All the three mismatches only very weakly disturb the overall B-form conformation of the duplex. Significant structural changes that occurred at the mismatch site are reflected mainly by the neighboring thymidine Raman bands at 1377, 1650, and 1675 cm(-1). The intensity change of the two latter bands is almost the same for the T:G and the T:T mismatch while in the case of the T:C mismatch it is just opposite, demonstrating a very different arrangement of the mismatched pair.     

C-type lectins L-SIGN and DC-SIGN capture and transmit infectious hepatitis C virus pseudotype particles

The molecular mechanisms involved in the hepatic tropism of hepatitis C virus (HCV) have not been identified. We have shown previously that liver-expressed C-type lectins L-SIGN and DC-SIGN bind the HCV E2 glycoprotein with high affinity (Lozach, P. Y., Lortat-Jacob, H., de Lacroix de Lavalette, A., Staropoli, I., Foung, S., Amara, A., Houles, C., Fieschi, F., Schwartz, O., Virelizier, J. L., Arenzana-Seisdedos, F., and Altmeyer, R. (2003) J. Biol. Chem. 278, 20358-20366). To analyze the functional relevance of this interaction, we generated pseudotyped lentivirus particles presenting HCV glycoproteins E1 and E2 at the virion surface (HCV-pp). High mannose N-glycans are present on E1 and, to a lesser extent, on E2 proteins of mature infectious HCV-pp. Such particles bind to both L-SIGN and DC-SIGN, but they cannot use these receptors for entry into cells. However, infectious virus is transmitted efficiently when permissive Huh-7 cells are cocultured with HCV-pp bound to L-SIGN or to DC-SIGN-positive cell lines. HCV-pp transmission via L-SIGN or DC-SIGN is inhibited by characteristic inhibitors such as the calcium chelator EGTA and monoclonal antibodies directed against lectin carbohydrate recognition domains of both lectins. In support of the biological relevance of this phenomenon, dendritic cells expressing endogenous DC-SIGN transmitted HCV-pp with high efficiency in a DC-SIGN-dependent manner. Our results support the hypothesis that C-type lectins such as the liver sinusoidal endothelial cell-expressed L-SIGN could act as a capture receptor for HCV in the liver and transmit infectious virions to neighboring hepatocytes.