Local neurogenic regulation of rat hindlimb circulation: CO2-induced release of calcitonin gene-related peptide from sensory nerves

Exploring Multifunctional Markers of Biological Age in Farmed Gilthead Sea Bream (Sparus aurata): A Transcriptomic and Epigenetic Interplay for an Improved Fish Welfare Assessment Approach

DNA methylation clocks provide information not only about chronological but also biological age, offering a high-resolution and precise understanding of age-related pathology and physiology. Attempts based on transcriptomic and epigenetic approaches arise as integrative biomarkers linking the quantification of stress responses with specific fitness traits and may help identify biological age markers, which are also considered welfare indicators. In gilthead sea bream, targeted gene expression and DNA methylation analyses in white skeletal muscle proved sirt1 as a reliable marker of age-mediated changes in energy metabolism. To complete the list of welfare auditing biomarkers, wide analyses of gene expression and DNA methylation in one- and three-year-old fish were combined. After discriminant analysis, 668 differentially expressed transcripts were matched with those containing differentially methylated (DM) regions (14,366), and 172 were overlapping. Through enrichment analyses and selection, two sets of genes were retained: 33 showing an opposite trend for DNA methylation and expression, and 57 down-regulated and hypo-methylated. The first set displayed an apparently more reproducible and reliable pattern and 10 multifunctional genes with DM CpG in regulatory regions (sirt1, smad1, ramp1, psmd2-up-regulated; col5a1, calcrl, bmp1, thrb, spred2, atp1a2-down-regulated) were deemed candidate biological age markers for improved welfare auditing in gilthead sea bream.

The Tissue Response to Hypoxia: How Therapeutic Carbon Dioxide Moves the Response toward Homeostasis and Away from Instability

Sustained tissue hypoxia is associated with many pathophysiological conditions, including chronic inflammation, chronic wounds, slow-healing fractures, microvascular complications of diabetes, and metastatic spread of tumors. This extended deficiency of oxygen (O₂) in the tissue sets creates a microenvironment that supports inflammation and initiates cell survival paradigms. Elevating tissue carbon dioxide levels (CO₂) pushes the tissue environment toward "thrive mode," bringing increased blood flow, added O₂, reduced inflammation, and enhanced angiogenesis. This review presents the science supporting the clinical benefits observed with the administration of therapeutic CO₂. It also presents the current knowledge regarding the cellular and molecular mechanisms responsible for the biological effects of CO₂ therapy. The most notable findings of the review include (a) CO₂ activates angiogenesis not mediated by hypoxia-inducible factor 1a, (b) CO₂ is strongly anti-inflammatory, (c) CO₂ inhibits tumor growth and metastasis, and (d) CO₂ can stimulate the same pathways as exercise and thereby, acts as a critical mediator in the biological response of skeletal muscle to tissue hypoxia.

Serum calcitonin gene-related peptide facilitates adipose tissue lipolysis during exercise via PIPLC/IP3 pathways

PURPOSE

Calcitonin gene-related peptide (CGRP) is formed by alternative transcription of the calcitonin/α-CGRP gene, which also gives rise to calcitonin (CT). Recently, CGRP has been the focus of research for its metabolic effects in vitro. In the present study, the in vivo effects of CGRP on epididymal fat pads lipolysis at rest and during exercise were investigated in trained male Wistar rats.

METHODS

Male Wistar rats were assigned to control and trained groups, which underwent endurance training for 12 weeks. The control (at rest) and trained (during acute exercise) animals were subjected to an intravenous injection of rat recombinant CGRP (2 µg kg^-1) and CGRP-(8-37), a competitive CGRP receptors antagonist, to evaluate if and how CGRP can affect adipose tissue lipolysis at rest and during exercise.

RESULTS

Intravenous injection of rat CGRP recombinant at rest upregulated major lipolysis pathways (cyclic AMP (cAMP), AMP-activated protein kinase (AMPK), and phospholipase C (PIPLC/IP₃)) in fat pads, causing an elevation in plasma-free fatty acid (FFA) and a decrease in plasma triglyceride (TG). All the effects were eliminated by pretreating the animals with CGRP-(8-37), suggesting that CGRP receptors were necessary for lipolytic effects of CGRP in fat pads. In trained animals, acute exercise augmented CGRP in serum, cerebrospinal fluid (CSF), and the cortex. Pretreating the animals with CGRP-(8-37) attenuated PIPLC/IP₃ pathway in fat pads and had no effect on cAMP and AMPK pathways.

CONCLUSIONS

Epididymal fat pads is a metabolic target for CGRP during exercise and CGRP effects on adipose tissue metabolism during exercise could be related to PIPLC/IP₃ pathway.

Sensory nerves and transient receptor potential vanilloid 1 channels in CO(2) regulation of cerebrovascular tone

This study investigated the involvement of sensory nerves and, in particular, neuronal transient receptor potential vanilloid (TRPV) 1 channels, in the CO(2)-mediated regulation of cerebrovascular tone. Basilar artery diameter and blood flow velocity in the ventral midbrain were determined in a rat cranial window preparation by digital imaging and laser-Doppler flowmetry, respectively. Superfusion of the basilar artery with capsaicin, a selective TRPV1 receptor agonist, caused a transient relaxation, consistent with acute desensitization of neuronal TRPV1 channels. Constriction to respiratory hypocapnia remained unaffected following capsaicin superfusion. Denervation of sensory nerves by repeated capsaicin injection of neonates also did not reduce the respiratory hypocapnia constriction of the basilar artery as well as the decreased flow velocity in the ventral midbrain in adults. These findings suggest that sensory nerves and, in particular, neuronal TRPV1 channels, do not play a role in respiratory hypocapnia constriction and decreased flow, at least in rat basilar artery and ventral midbrain.

Differential distribution of vanilloid receptors in the primary sensory neurons projecting to the dorsal skin and muscles

We examined transient receptor potential (TRP) V1 and TRPV2 expression in calcitonin gene-related peptide (CGRP) positive (+) primary sensory neurons projecting to the skin and skeletal muscles of the rat dorsum. Among the dorsal root ganglia at the levels from C2 to Th1, 34.9% of neurons projecting to the skin were positive for CGRP, and 32.6% or 21.6% of neurons projecting to the trapezius muscle or the longissimus muscle were positive for CGRP. Of the small CGRP+ neurons projecting to the skin, 53.5% were positive for TRPV1, 11.6% were positive for TRPV2. Of the small CGRP+ neurons projecting to the trapezius or the longissimus, 53.1 or 53.2% were positive for TRPV1, 8.8 or 8.3% were positive for TRPV2, respectively. In the periphery, 29.3% of CGRP+ nerve fibers were positive for TRPV1 in the skin, whereas 65.0 or 59.8% were positive in the trapezius or the longissimus. Therefore, the present study showed that the percentage of CGRP+ neurons projecting to the trapezius is higher than that to the longissimus, and that the co-localization percentage of CGRP and TRPV1 on the sensory nerves was also higher in the trapezius than in the longissimus and the skin.

Sensory neurons with afferents from hind limbs: enhanced sensitivity in secondary hypertension

Sensory nerve fibers from the dorsal root ganglia (DRG) may contribute to the regulation of peripheral vascular resistance. Axons of DRG neurons of the lower thoracic cord project mainly to resistance vessels in the lower limbs, likely opposing the vasoconstrictor effects of the sympathetic activity. This mechanism might be of importance in hypertension with increased sympathetic activity. We tested the hypothesis that sensory neurons of the DRG in the lower thoracic cord show an altered sensitivity to mechanical stimuli in hypertension. Neurons from DRG (T11 to L1) of rats with hypertension (2 kidney-1 clip hypertensive rats and 5 of 6 nephrectomized rats) were cultured on coverslips. Current time relationships were established with whole-cell patch recordings. Cells were characterized under control conditions and after exposure to hypoosmotic solutions to induce mechanical stress. Neurons with projections to the kidney were studied for comparison. The hypoosmotic extracellular medium induced a significant change in conductance of the cells in all of the groups of rats. In hypertensive rats, responses of cells with hindlimb axons were significantly different from controls: (2 kidney-1 clip hypertensives: delta-351+/-52 pA and 5 of 6 nephrectomized rats: delta-372+/-43 pA versus controls: delta-190+/-25 pA; P<0.05). Responses of DRG cells with renal afferents to mechanical stress were unaffected. Neurons from DRG in the lower thoracic cord with projections to the lower limbs exhibited an increased sensitivity to mechanical stress. We speculate that this observation may indicate an increased activity of these neurons, their axons, and neurotransmitters in the control of resistance vessels in hypertension.

Differential development of TRPV1-expressing sensory nerves in peripheral organs

In mouse ontogeny, neurons immunoreactive for transient receptor potential vanilloid receptor 1 (TRPV1) were observed primarily in the dorsal root ganglia (DRG) at embryonic day 13 (E13). In the embryonic period, the number of TRPV1(+) neurons decreased, but then gradually increased postnatally. Some of TRPV1(+) neurons were also immunoreactive for calcitonin gene-related peptide (CGRP). At postnatal day 7 (P7), 66% of CGRP(+) neurons were TRPV1(+), and 55% of TRPV1(+) neurons were also CGRP(+) in the L4 DRG. In the peripheral organs, TRPV1-immunorective nerve fibers were transiently observed in the skin at E14. They were also observed in the urinary tract at E14, and in the rectum at E15. Many TRPV1(+) nerve fibers in these organs were also CGRP(+). At P1, TRPV1(+) nerve fibers were observed in the respiratory organs, and to a lesser extent in the stomach, colon, skin, and skeletal muscles. The number of TRPV1(+) nerve fibers on each organ gradually increased postnatally. At P7, TRPV1(+) nerve fibers were also observed in the small intestine and kidneys. The percentage of total TRPV1(+) nerve fibers that co-localized with CGRP was greater in most organs at P7 than at P1. The present results indicate that TRPV1 expression on peripheral processes differs among organs. The differential time course of TRPV1 expression in the cell bodies might be related to the organs to which they project. Co-localization of TRPV1 with CGRP on nerve fibers also varies among organs. This suggests that the TRPV1-mediated neuropeptide release that occurs in certain pathophysiologic conditions also varies among organs.

Cloning and transcriptional analysis of the mouse receptor activity modifying protein-1 gene promoter

BACKGROUND

Receptor activity modifying protein-1 (RAMP-1) is a single transmembrane-domain protein required for the functional expression of calcitonin gene-related peptide (CGRP) receptors. To date, little is known about the molecular mechanism(s) that activate/inhibit RAMP-1 gene expression. Such mechanism(s) are likely to play a major role in modulating the responsiveness of tissues to CGRP.

RESULTS

To initiate studies on the transcriptional regulation of the mouse RAMP-1 gene, RAMP-1 transcriptional initiation sites were mapped in a variety of tissues. Analysis of RAMP-1 expression in C2C12 myoblasts demonstrated that RAMP-1 mRNA is expressed at greatest levels in confluent myoblasts verses non-confluent and fused myoblasts. Transfection of confluent C2C12 myoblasts and NIH 3T3 cells with RAMP-1 promoter/luciferase deletion constructs revealed that 4.7 kb of RAMP-1 5' flanking region demonstrated optimal promoter activity while 343 bp of 5' flanking region was defined as a minimal RAMP-1 promoter. In non-RAMP-1 expressing HEK293 cells, constructs containing 4.7 kb to 782 bp of RAMP-1 5' flanking region were transcriptionally inactive. However, deletion of sequences -782 to -343 activated RAMP-1 promoter activity.

CONCLUSION

These findings suggest that tissue specificity of RAMP-1 gene expression is mediated by a negative acting transcription factor that represses RAMP-1 gene expression in non-RAMP-1 expressing tissues. This transcription factor is therefore likely to play an important role in modulating the responsiveness of tissues to CGRP.

Localization of the calcitonin gene-related peptide receptor complex at the vertebrate neuromuscular junction and its role in regulating acetylcholinesterase expression

The calcitonin gene-related peptide (CGRP) is released by motor neurons where it exerts both short and long term effects on skeletal muscle fibers. In addition, sensory neurons release CGRP on the surrounding vasculature where it is in part responsible for local vasodilation following muscle contraction. Although CGRP-binding sites have been demonstrated in whole muscle tissue, the type of CGRP receptor and its associated proteins or its cellular localization within the tissue have not been described. Here we show that the CGRP-binding protein referred to as the calcitonin receptor-like receptor is highly concentrated at the avian neuromuscular junction together with its two accessory proteins, receptor activity modifying protein 1 and CGRP-receptor component protein, required for ligand specificity and signal transduction. Using tissue-cultured skeletal muscle we show that CGRP stimulates an increase in intracellular cAMP that in turn initiates down-regulation of acetylcholinesterase expression at the transcriptional level, and, more specifically, inhibits expression of the synaptically localized collagen-tailed form of the enzyme. Together, these studies suggest a specific role for CGRP released by spinal cord motoneurons in modulating synaptic transmission at the neuromuscular junction by locally inhibiting the expression of acetylcholinesterase, the enzyme responsible for terminating acetylcholine neurotransmission.

Cardiovascular and vocalization reactions elicited by N-methyl-D-aspartate in the pretentorial periaqueductal grey of cats

1. Cats were anaesthetized with urethane (1100-1200 mg/kg, i.p.), supplemented with halothane inhalation during surgery. Responses in terms of systemic arterial pressure, mean systemic arterial pressure(MSAP), heart rate, mean blood flow of the common carotid artery and femoral artery, amplitude and frequency of vocalizations, thoracic-abdominal contractions and limb movements were recorded. 2. Microinjection of N-methyl-D-aspartate (NMDA; 20 mmol/L, 200 nL) into the pretentorial periaqueductal grey (PAG) produced two classes of response: (i) cardiovascular responses and vocalization; and (ii) cardiovascular responses without vocalization. 3. For class 1 responses, five types of vocalization concomitant with pressor (VPR) or depressor (VDPR) responses were observed: (i) type 1 VDPR and VPR, elicited in the rostral and caudal part of the dorsal PAG, produced vocalization of slight hissing, with or without limb movement, moderately increased flow of the common carotid and slightly increased flow of the femoral arteries; (ii) types 2 and 3 VPR, elicited in the dorsolateral and intermediate-lateral PAG, produced hissing-howling and growling, increased respiratory movement, with or without repetitive burst limb movements or stretching of paws, slightly decreased common carotid artery flow and inconsistent changes (increased or decreased slightly) in femoral artery flow; (iii) type 4 VPR, elicited in the dorsomedial and intermediate-medial PAG, produced meowing-crying but without limb movements, common carotid artery flow was increased, but the femoral artery flow was slightly decreased or increased markedly; and (iv) type 5 VPR, elicited in the ventromedial PAG, produced meowing-screaming with or without limb movements, common carotid artery flow increased moderately and femoral artery flow increased markedly. Vocalization was loud and wild in type 4 and 5 responses. 4. For class 2 responses, two types of responses were observed: (i) a pressor response (PR) alone, elicited in the dorsolateral and intermediate-lateral PAG, produced inconsistent changes in common carotid and femoral artery flow, which increased, decreased or underwent no change; and (ii) a depressor response (DPR) elicited in the ventrolateral PAG produced moderate increases of common carotid and femoral artery flow. 5. The reduction of resistance in the femoral artery was more prominent (P < 0.05) in type 1 VDPR than in DPR. Similar changes occurred in the femoral artery among types 3 (P < 0.05) and 5 VPR (P < 0.005) and PR. In addition, the frequency of vocalization was significantly positively correlated with the increase in MSAP (P < 0.05) and mean common carotid and femoral artery flow (both P < 0.01) in all types of VPR. 6. These results suggest the presence of neurons involved in the expression of defence reactions in a longitudinal, complicated functional organization in the entire PAG column. In particular, NMDA stimulation of the medial, dorsal and dorsolateral PAG may elicit five different types of defence reactions, expressed by various forms of cardiovascular alterations concomitant with vocalization responses.

Effects of normobaric hyperoxia on water content in different organs in rats

Pulmonary oxygen toxicity is a dose-dependent effect on alveolar epithelial and endothelial cells resulting in pulmonary oedema. Any concomitant effects on systemic capillary endothelium would be expected to result in capillary leakage and an increase in the tissues' water content. Total tissue water (TTW) in different organs was therefore studied in freely moving rats exposed to 100% O2 at normobaric pressure for 24 or 48 h, and compared to air-breathing control rats. The TTW for the following tissues was measured: Trachea, left bronchus, left lung, left and right ventricle, left kidney, skin (left paw-hindlimb), skin (back of the rat), left brain, left eye and thigh muscle left side. There was a significant increase in TTW of the lung accompanied by pleural effusion after 48 h of oxygen exposure as expected in all exposed animals. There was a small increase in TTW of the paw only, and a small decrease or no change in other tissues after 24 and 48 h of exposure. We conclude that there is no evidence of systemic capillary dysfunction as measured by tissue water content after exposure to hyperoxia in a dosage causing pulmonary oedema.