Extracellular signal-regulated kinase and phosphatidylinositol-3-kinase/AKT signalling pathways in the human carotid body and peripheral ganglia

Inhibition of Protein Kinases AKT and ERK1/2 Reduce the Carotid Body Chemoreceptor Response to Hypoxia in Adult Rats

The carotid body is the main mammalian oxygen-sensing organ regulating ventilation. Despite the carotid body is subjected of extensive anatomical and functional studies, little is yet known about the molecular pathways signaling the neurotransmission and neuromodulation of the chemoreflex activity. As kinases are molecules widely involved in motioning a broad number of neural processes, here we hypothesized that pathways of protein kinase B (AKT) and extracellular signal-regulated kinases ½ (ERK1/2) are implicated in the carotid body response to hypoxia. This hypothesis was tested using the in-vitro carotid body/carotid sinus nerve preparation ("en bloc") from Sprague Dawley adult rats. Preparations were incubated for 60 min in tyrode perfusion solution (control) or containing 1 μM of LY294002 (AKT inhibitor), or 1 μM of UO-126 (ERK1/2 inhibitor). The carotid sinus nerve chemoreceptor discharge rate was recorded under baseline (perfusion solution bubbled with 5 % CO(2) balanced in O(2)) and hypoxic (perfusion solution bubbled with 5 % CO(2) balanced in N(2)) conditions. Compared to control, both inhibitors significantly decreased the normoxic and hypoxic carotid body chemoreceptor activity. LY294002- reduced carotid sinus nerve discharge rate in hypoxia by about 20 %, while UO-126 reduces the hypoxic response by 45 %. We concluded that both AKT and ERK1/2 pathways are crucial for the carotid body intracellular signaling process in response to hypoxia.

Expression of leptin and leptin receptor isoforms in the rat and human carotid body

Leptin is known to play a role in the modulation of metabolism and control of breathing acting mainly on central nervous structures, although additional actions on peripheral arterial chemoreceptors have also been suggested in the literature. We therefore examined by means of immunohistochemistry the expression of leptin and leptin receptors in the carotid bodies of rats and humans. Leptin expression and relative expression of leptin receptor isoforms were also studied in rats by real-time PCR. No leptin or leptin receptor immunoreactivities were visible in the type II cells of either series. In rat carotid bodies, diffuse positive stainings for leptin and leptin receptors (both with antibody recognizing all receptor isoforms and antibody specific for Ob-Rb) were observed in type I cells. In human carotid bodies, the mean percentage (±standard error) of leptin immunoreactive type I cells was 39.4%±5.1% and the percentages of leptin receptor immunoreactive type I cells were 57.3%±3.9% with antibody recognizing all receptor isoforms and 33.3%±4.2% with antibody specific for isoform Ob-Rb. Double immunofluorescences with anti-tyrosine hydroxylase (type I cell marker) and anti-glial fibrillary acidic protein (type II cell markers) confirmed the selective location of leptin and Ob-Rb in type I cells. Real-time PCR showed the expression of leptin and Ob-Ra, Ob-Rb, Ob-Rc and Ob-Rf isoform mRNA in the rat carotid body, levels of expression being Ob-Rf>Ob-Rc>>Ob-Ra>>Ob-Rb. Ob-Re mRNA was not detected. The above findings suggest a role of circulating or locally produced leptin in the regulation of chemoreceptor discharge and/or metabolic sensing function, by means of direct action on type I cells.

Neurotensin receptor 1 immunoreactivity in the peripheral ganglia and carotid body

In the present study we investigated, through immunohistochemistry, the presence and location of neurotensin receptor 1 (NTR1) in the peripheral ganglia and carotid body of 16 humans and 5 rats. In both humans and rats, NTR1 immunostained ganglion cells were found in superior cervical ganglia (57.4±11.6% and 72.4±11.4%, respectively, p<0.05), enteric ganglia (51.9±10.4% and 64.6±6.1%, p<0.05), sensory ganglia (69.2±10.7% and 73.0±13.1%, p>0.05) and parasympathetic ganglia (52.1±14.1% and 59.4±14.0%, p>0.05), supporting a modulatory role for NT in these ganglia. Positivity was also detected in 45.6±9.2% and 50.8±6.8% of human and rat type I glomic cells, respectively, whereas type II cells were negative. Our findings suggest that NT produced by type I cells acts in an autocrine or paracrine way on the same cell type, playing a modulatory role on chemoception.