Biomedical subjects

Michal Horowitz

Publications and source records attributed to Michal Horowitz.

14 recordsLinked to original sources

PubMed2006

Acclimatory-phase specificity of gene expression during the course of heat acclimation and superimposed hypohydration in the rat hypothalamus.

The induction of the heat-acclimated phenotype involves reprogramming the expression of genes encoding both constitutive and inducible proteins. In this investigation, we studied the global genomic response in the hypothalamus during heat acclimation, with and without combined hypohydration stress. Rats were acclimated for 2 days (STHA) or for 30 days (LTHA) at 34 degrees C. Hypohydration (10% decrease in body weight) was attained by water deprivation. 32P-labeled RNA samples from the hypothalamus were hybridized onto cDNA Atlas array (Clontech no. 1.2) membranes. Clustering and functional analyses of the expression profile of a battery of genes representing various central regulatory functions of body homeostasis demonstrated a biphasic acclimation profile with a transient upregulation of genes encoding ion channels, transporters, and transmitter signaling upon STHA. After LTHA, most genes returned to their preacclimation expression levels. In both STHA and LTHA, genes encoding hormones and neuropeptides, linked with metabolic rate and food intake, were downregulated. This genomic profile, demonstrating an enhanced transcription of genes linked with neuronal excitability during STHA and enhanced metabolic efficiency upon LTHA, is consistent with our previously established integrative acclimation model. The response to hypohydration was characterized by an upregulation of a large number of genes primarily associated with the regulation of ion channels, cell volume, and neuronal excitability. During STHA, the response was transiently desensitized, recovering upon LTHA. We conclude that hypohydration overrides the heat acclimatory status. It is notable that STHA and hypohydration gene profiles are analogous with the physiological profile described in the response to various types of brain injury.

Acclimatization↗

PubMed2006

N-arachidonoyl L-serine, an endocannabinoid-like brain constituent with vasodilatory properties.

The endocannabinoid N-arachidonoyl ethanolamine (anandamide), found both in the CNS and in the periphery, plays a role in numerous physiological systems. One might expect that the chemically related N-arachidonoyl-L-serine (ARA-S) could also be formed alongside anandamide. We have now isolated ARA-S from bovine brain and elucidated its structure by comparison with synthetic ARA-S. Contrary to anandamide, ARA-S binds very weakly to cannabinoid CB1 and CB2 or vanilloid TRPV1 (transient receptor potential vanilloid 1) receptors. However, it produces endothelium-dependent vasodilation of rat isolated mesenteric arteries and abdominal aorta and stimulates phosphorylation of p44/42 mitogen-activated protein (MAP) kinase and protein kinase B/Akt in cultured endothelial cells. ARA-S also suppresses LPS-induced formation of TNF-alpha in a murine macrophage cell line and in wild-type mice, as well as in mice deficient in CB1 or CB2 receptors. Many of these effects parallel those reported for abnormal cannabidiol (Abn-CBD), a synthetic agonist of a putative novel cannabinoid-type receptor. Hence, ARA-S may represent an endogenous agonist for this receptor.

Animals↗

PubMed2005

Heat intolerance: does gene transcription contribute?

During exertion in the heat, heat-intolerant (HI) subjects have a physiological disability in metabolic heat dissipation. The HI state is either permanent or temporary, depending on whether it stems from transient predisposing factors or inherent thermoregulatory dysfunction. In this investigation, we studied protein levels of heat shock protein (HSP) 70 and HSP72, HSP90, bcl-2xL, glutathione S-transferase-p, heat shock factor-1, TATA-binding protein-associated factor, and NF-kappaB transcripts using Western blot and quantitative RT-PCR, respectively, in lymphocytes of HI and tolerant (T) male volunteers of similar anthropometric features. Measurements were made from blood drawn before, during the heat tolerance test (3.5 mph, 40 degrees C, 40% relative humidity, 2 h), and 1 h after recovery at 24 degrees C. Rectal and skin temperatures, as well as heart rate, were continuously recorded. Of 58 subjects, 7 were identified as HI, with a significantly higher physiological strain index than in the T group (6.3 +/- 0.9 vs. 3.8 +/- 0.6, P < 0.001). The responsiveness of the vasculature to thermal stimuli was decreased in the HI group, as indicated by rectal temperature minus skin temperature. The HSP72 level in the HI group dropped during the recovery session (P < 0.01), whereas that of the T group continued to rise. A significantly increased expression of the transcription factors in the T subjects and significantly decreased expression in the HI group (P < 0.009, 0.013, and 0.005 for heat shock factor-1, NF-kappaB, and TATA-binding protein-associated factor, respectively) points to impaired transcriptional processes in the HI group. Our data suggest that transcriptional malfunction and sluggishness of the vasculature to thermal stimuli are predisposing factors in the HI group.

Adult↗

PubMed2005

HIF-1alpha-targeted pathways are activated by heat acclimation and contribute to acclimation-ischemic cross-tolerance in the heart.

Hypoxia-inducible factor-1 (HIF-1) is a key regulator of the cellular hypoxic response. We previously showed that HIF-1 activation is essential for heat acclimation (AC) in Caenorhabditis elegans. Metabolic changes in AC rat hearts indicate HIF-1alpha activation in mammals as well. Here we characterize the HIF-1alpha profile and the transcriptional activation of its target genes following AC and following heat stress (HS) in hearts from nonacclimated (C; 24 degrees C) and AC (34 degrees C, 1 mo) rats. We used Western blot and immunohistochemistry to measure HIF-1alpha levels and EMSA and RT-PCR/quantitative RT-PCR to detect expression of the HIF-1alpha-targeted genes, including vascular endothelial growth factor (Vegf), heme oxygenase-1 (HO1), erythropoietin (Epo), and Epo receptor (EpoR). EpoR and Epo mRNA levels were measured to determine systemic effects in the kidneys and cross-tolerance effects in C and AC ischemic hearts (Langendorff, 75% ischemia, 40 min). The results demonstrated that 1) after AC, HIF-1alpha protein levels were increased, 2) HS alone induced transient HIF-1alpha upregulation, and 3) VEGF and HO1 mRNA levels increased after HS, with greater magnitude in the AC hearts. Epo mRNA in AC kidneys and EpoR mRNA in AC hearts were also elevated. In AC hearts, EpoR expression was markedly higher after HS or ischemia. Hearts from AC rats were dramatically protected against infarction after ischemia-perfusion. We conclude that HIF-1 contributes to the acclimation-ischemia cross-tolerance mechanism in the heart by induction of both chronic and inducible adaptive components.

Animals↗

PubMed2005

Heat acclimation increases hypoxia-inducible factor 1alpha and erythropoietin receptor expression: implication for neuroprotection after closed head injury in mice.

Experimental evidence indicates that long-term exposure to moderately high ambient temperature (heat acclimation, HA) mediates cross-tolerance to various types of subsequently applied stress. The transcriptional activator hypoxia-inducible factor 1 (HIF-1) has been implicated in playing a critical role in HA. It also regulates the expression of Erythropoietin (Epo), whose neuroprotective effects have been shown in a variety of brain injuries. The aim of the present study was to examine whether HA exerts a beneficial effect on the outcome of closed head injury (CHI) in mice and to explore the possible involvement of HIF-1 and Epo in this process. Heat acclimated mice and matched normothermic controls were subjected to CHI or sham surgery. Postinjury motor and cognitive parameters of acclimated mice were compared with those of controls. Mice were killed at various time points after injury or sham surgery and brain levels of HIF-1alpha, the inducible subunit of HIF-1, Epo, and the specific erythropoietin receptor (EpoR) were analyzed by Western immunoblotting. Motor and cognitive functions of acclimated mice were significantly better than those of controls. Heat acclimation was found to induce a significant increase in expression of nuclear HIF-1alpha and EpoR. The EpoR/Epo ratio was also significantly higher in acclimated mice as compared with controls. Nuclear HIF-1alpha and EpoR were higher in the acclimated group at 4 h after injury as well. The improved outcome of acclimated mice taken together with the basal and postinjury upregulation of the examined proteins suggests the involvement of this pathway in HA-induced neuroprotection.

Acclimatization↗

PubMed2004

Prior heat acclimation confers protection against noise-induced hearing loss.

Exposure to intense noise stress can cause a permanent noise-induced hearing loss which is thought to be due to elevation of reactive oxygen species in excess of the inherent antioxidant mechanisms of the cell. However, preconditioning to low levels of stress of one type can activate cellular mechanisms leading to the elevation of antioxidant levels so that the cell is then better able to tolerate subsequent severe stress of a different type. This has been called cross-tolerance. Here, we tested this hypothesis by acclimating rats to a moderate heat stress (30 days at 34 degrees C). The rats were exposed to 113 dB SPL noise for 3 days (12 h/day) in three different groups: heat acclimated then noise exposed; noise exposed and then heat acclimated; heat acclimated, then noise exposed and then heat acclimated again. Permanent changes in auditory function--auditory nerve brainstem evoked responses (ABR) and distortion product otoacoustic emissions (DPOAEs)--were evaluated in each of these animals and compared with those in rats exposed to noise only and in control groups of rats. Statistical evaluation of the results showed that when assessed with ABR, each of the heat-acclimated, noise-exposed groups was protected from the noise, even the group that was heat-acclimated after the noise exposure. When assessed with DPOAE, protection was statistically apparent only in the group that was heat acclimated, then exposed to noise, and not in the other groups. Thus, heat acclimation provides protection against permanent noise-induced hearing loss.

Acclimatization↗

PubMed2004

Stress-related genomic responses during the course of heat acclimation and its association with ischemic-reperfusion cross-tolerance.

Acclimation to heat is a biphasic process involving a transient perturbed phase followed by a long lasting period during which acclimatory homeostasis is developed. In this investigation, we used cDNA stress microarray (Clontech Laboratory) to characterize the stress-related genomic response during the course of heat acclimation and to test the hypotheses that 1) heat acclimation influences the threshold of activation of protective molecular signaling, and 2) heat-acclimation-mediated ischemic-reperfusion (I/R) protection is coupled with reprogrammed gene expression leading to altered capacity or responsiveness of protective-signaling pathways shared by heat and I/R cytoprotective systems. Rats were acclimated at 34 degrees C for 0, 2, and 30 days. 32P-labeled RNA samples prepared from the left ventricles of rats before and after subjection to heat stress (HS; 2 h, 41 degrees C) or after I/R insult (ischemia: 75%, 45 min; reperfusion: 30 min) were hybridized onto the array membranes. Confirmatory RT-PCR of selected genes conducted on samples taken at 0, 30, and 60 min after HS or total ischemia was used to assess the promptness of the transcriptional response. Cluster analysis of the expressed genes indicated that acclimation involves a "two-tier" defense strategy: an immediate transient response peaking at the initial acclimating phase to maintain DNA and cellular integrity, and a sustained response, correlated with slowly developed adaptive, long-lasting cytoprotective signaling networks involving genes encoding proteins that are essential for the heat-shock response, antiapoptosis, and antioxidation. Gene activation was stress specific. Faster activation and suppression of signaling pathways shared by HS and I/R stressors probably contribute to heat-acclimation I/R cross-tolerance.

Acclimatization↗

PubMed2003

HIF-1 is required for heat acclimation in the nematode Caenorhabditis elegans.

Chronic exposure to environmental heat improves tolerance via heat acclimation (AC). Our previous data on mammals indicate that reprogramming the expression of genes coding for stress proteins and energy-metabolism enzymes plays a major role. Knowledge of pathways leading to AC is limited. For their identification, we established a Caenorhabditis elegans AC model and tested mutants in which signaling pathways pertinent to acclimatory responses are mutated. AC attained by maintaining adult C. elegans at 25 degrees C for 18 h enhanced heat endurance of wild-type worms subjected to heat stress (35 degrees C) and conferred protection against hypoxia and cadmium. Survival curves demonstrated that both daf-2 (insulin receptor pathway) showing enhanced heat tolerance and daf-16 loss-of-function (a transcription factor mediating DAF-2 signaling) mutants benefit from AC, suggesting that the insulin receptor pathway does not mediate AC. In contrast, the hif-1 (hypoxia inducible factor) loss-of-function strain did not show acclimation, and non-acclimated vhl-1 and egl-9 mutants (overexpressing HIF-1) had greater heat endurance than the wild type. Like mammals, HIF-1 and HSP72 levels increased in the wild-type AC nematodes. HSP72 upregulation in AC hif-1 mutants was also observed; however, it was insufficient to improve heat/stress tolerance, suggesting that HIF-1 upregulation is essential for acclimation, whereas HSP72 upregulation in the absence of HIF-1 is inadequate. We conclude that HIF-1 upregulation is both an evolutionarily conserved and a necessary component of heat acclimation. The known targets of HIF-1 imply that metabolic adaptations are essential for AC-dependent tolerance to heat and heavy metals, in addition to their known role in hypoxic adaptation.

Acclimatization↗

PubMed2003

Matching the heart to heat-induced circulatory load: heat-acclimatory responses.

Heat acclimation enhances cardiac efficiency by increasing stroke volume and decreasing heart rate. These adaptations involve biochemical changes in the contractile apparatus, switched on by altered expression of genes coding contractile and calcium-regulatory proteins and partially mediated by persistent low thyroxine. Heat acclimation also produces cross-tolerance to oxygen deprivation, thus reinforcing cardiac adaptation to oxygen demand/supply mismatching via energy-sparing pathways.

Acclimatization↗

PubMed2002

Heat acclimation-induced elevated glycogen, glycolysis, and low thyroxine improve heart ischemic tolerance.

Based on our observations of energy sparing in heat-acclimated (AC) rat hearts, we investigated whether changes in preischemic glycogen level, glycolytic rate, and plasma thyroxine level mediate cardioprotection induced in these hearts during ischemia-reperfusion insults. Control (C) (24 degrees C), AC (34 degrees C, 30 days), acclimated-euthyroid (34 degrees C + 3 ng/ml l-thyroxine), and control hypothyroid (24 degrees C + 0.02% 6-n-propyl-2-thiouracil) groups were studied. Preischemic glycogen was higher in AC than in C hearts [39.0 +/- 8.5 vs. 19.2 +/- 4.2 (SE) micromol glucose/g wet wt; P < 0.0006], and the lactate produced vs. glycogen level during total ischemia ((13)C-NMR spectroscopy) was markedly slower (AC: -0.82x, r = 0.98 vs. C: -4.7x, r = 0.9). Time to onset of ischemic contracture was lengthened, and the fraction of hearts experiencing ischemic contracture was lowered. Pulse pressure recovery was improved in AC compared with C animals before, but not after, absolute sodium iodoacetate-induced glycolysis inhibition. Acclimated-euthyroid hearts exhibited decreased ischemic tolerance, whereas induced hypothyroidism in C improved cardiotolerance. Thus higher preischemic glycogen and slowed glycolysis are associated with hypothyroidism and are likely important mediators of the improved ischemic tolerance exhibited by AC hearts.

Acclimatization↗

PubMed2002

From molecular and cellular to integrative heat defense during exposure to chronic heat.

Heat acclimation induces adaptive changes that improve the ability to cope with extreme environmental heat. Acclimatory homeostasis is manifested by an expanded dynamic thermoregulatory span (TRS), reflected in the intact organism by a lower temperature threshold (T(sh)) for heat dissipation, and delayed T(sh) for thermal injury. This principle shares common adaptive features with each of the thermoregulatory effectors. In the splanchnic circulation, e.g. the TRS of the thermally induced vasomotor response increases due to greater cardiac output distribution to the splanchnic vasculature, thereby increasing circulatory reserves and delaying thermal injury. During short-term heat acclimation (STHA), accelerated autonomic excitability plays a major role in the control of body temperature. Acclimatory homeostasis, however, is achieved only following long-term heat acclimation (LTHA), and is characterized by increased thermal effector efficiency, namely [effector organ output/autonomic signal] ratio >1. Two acclimatory responses, derived from our data on the acclimating rat model, are discussed: (1) acclimation of the cholinergic-muscarinic signaling for water secretion in the submaxillary gland; and (2) acclimatory mechanisms for increased contractile efficiency in the heart. Our data indicate that increased efficiency upon LTHA develops by reprogramming of gene expression. A reduced thyroid hormone level is responsible for some of the molecular adaptive cascades. Delayed thermal injury observed upon acclimation is due to enhanced cytoprotective mechanisms of which the inducible heat shock protein (HSP) 72 kDa plays a major role. Our data indicate that heat acclimation predisposes the HSP molecular machinery to respond faster and increases the constitutive level of the protein. STHA is the time-window during which most LTHA adaptations are switched on.

Adaptation, Physiological↗

PubMed2002

Heat acclimation in rats: modulation via lipid polyunsaturation.

Heat acclimation of rats has been shown to enhance endurance of rat hearts to ischemic insult and acute heat stress. Common protective features have been shown to be operative during both these stress-inducing conditions. To explore the role of membrane lipid composition in the adaptive response, we analyzed two major parameters that impact membrane dynamics and order, the nonesterified cholesterol levels and the acyl chain composition of phospholipids, in rat heart and salivary glands, both major thermoregulatory organs, in short- and long-term heat-acclimated rats. Before exposure to heat, control salivary gland tissue has a higher cholesterol-to-phospholipid mole ratio (0.32 +/- 0.02) than heart (0.14 +/- 0.01), and the acyl chains of its phospholipids are 50% more saturated. The remodeling strategies of the tissues after exposure to heat differed. Heart cholesterol levels increased after short-term heat acclimation (approximately 50%), whereas salivary gland cholesterol levels decreased in acute heat stress and long-term heat acclimation (approximately 32%). Remodeling of phospholipid acyl chains, particularly an increase in docosahexaenoic acid, was a protective strategy in both tissues (57% in heart and >100% in salivary glands). Modifying membrane lipid composition by treating rats with liposomes composed of egg phosphatidylcholine (PC) before exposure to heat resulted in a 38% increase in endurance to thermal stress. The density and affinity of muscarinic receptors of submaxillary salivary glands, involved in the acclimation response, were measured in control and PC liposome-treated rats, and then both groups were subjected to short-term heat acclimation. After PC treatment the well-established compensatory upregulation of the muscarinic receptors and concomitant decrease in their affinity was blunted. The substantial increase in the thermal endurance of heat-challenged intact rats after treatment with PC liposomes (600 vs. 200 min) suggests that membrane lipid composition plays a role in the ability of these tissues to respond to heat stress.

Adaptation, Physiological↗

PubMed2002

beta-Adrenergic signaling and thyroid hormones affect HSP72 expression during heat acclimation.

Heat acclimation upregulates 72-kDa heat shock protein (HSP72) and predisposes to faster activation of the heat shock response (HSR). This study investigates the role played by beta-adrenergic signaling and/or plasma thyroxine level in eliciting these features by using rats undergoing 1) heat acclimation (AC; 34 degrees C, 2 and 30 days); 2) AC with beta-adrenergic blockade; 3) AC-maintained euthyroid; 4) hypothyroid; 5) hyperthyroid; and 6) controls. The hsp72 mRNA (RT-PCR) and HSP72 levels (Western blot) were measured before and after heat stress (2 h, 41 degrees C, rectal temperature monitored). beta-Adrenergic blockade during AC abolished HSP72 accumulation, without disrupting HSR. Low thyroxine blunted the HSR at posttranscriptional level, whereas thyroxine administration in hyperthyroid and AC-maintained euthyroid rats arrested heat stress-evoked hsp72 transcription. We conclude that beta-adrenergic signaling contributes to the high HSP72 level characterizing the AC state. Thyroxine has two opposing effects: 1) direct repressive on rapid hsp72 transcription after heat stress; and 2) indirect stimulatory via beta-adrenergic signaling. Low thyroxine could account for diminished HSP72 synthesis via lower heat production and thermoregulatory set point.

Acclimatization↗

PubMed1998

Do Cellular Heat Acclimation Responses Modulate Central Thermoregulatory Activity?

The classical concept of heat acclimation is of an autonomically controlled array of integrative physiological processes, improving heat tolerance. New evidence suggests that a temporal interplay between opposing autonomic and peripheral cell-originated responses, switched on by heat and autonomic stimulation of the cell membrane, and a marked increase in the stock of the inducible 70-kDa heat shock protein contribute to widening of the thermoregulatory activity span.

Journal Article↗