Key pointsr Activation of central chemoreceptors by CO 2 increases sympathetic nerve activity (SNA), arterial blood pressure (ABP) and breathing. These effects are exaggerated in spontaneously hypertensive rats (SHRs), resulting in an augmented CO 2 chemoreflex that affects both breathing and ABP. r The orexin system is overactive in SHRs and contributes to the augmented CO 2 chemoreflex and hypertension. Modulation of the orexin system may be beneficial in the treatment of neurogenic hypertension.Abstract Activation of central chemoreceptors by CO 2 increases arterial blood pressure (ABP), sympathetic nerve activity and breathing. In spontaneously hypertensive rats (SHRs), high ABP is associated with enhanced sympathetic nerve activity and peripheral chemoreflexes. We hypothesized that an augmented CO 2 chemoreflex and overactive orexin system are linked with high ABP in both young (postnatal day 30-58) and adult SHRs (4-6 months). Our main findings are as follows. (i) An augmented CO 2 chemoreflex and higher ABP in SHRs are measureable at a young age and increase in adulthood. In wakefulness, the ventilatory response to normoxic hypercapnia is higher in young SHRs (mean ± SEM: 179 ± 11% increase) than in age-matched normotensive Wistar-Kyoto rats (114 ± 9% increase), but lower than in adult SHRs (226 ± 10% increase; P < 0.05). The resting ABP is higher in young SHRs (122 ± 5 mmHg) than in age-matched Wistar-Kyoto rats (99 ± 5 mmHg), but lower than in adult SHRs (152 ± 4 mmHg; P < 0.05).(ii) Spontaneously hypertensive rats have more orexin neurons and more CO 2 -activated orexin neurons in the hypothalamus. (iii) Antagonism of orexin receptors with a dual orexin receptor antagonist, almorexant, normalizes the augmented CO 2 chemoreflex in young and adult SHRs and the high ABP in young SHRs and significantly lowers ABP in adult SHRs. (iv) Attenuation of peripheral chemoreflexes by hyperoxia does not abolish the augmented CO 2 chemoreflex (breathing and ABP) in SHRs, which indicates an important role for the central chemoreflex. We suggest that an overactive orexin system may play an important role in the augmented central CO 2 chemoreflex and in the development of hypertension in SHRs.

The development and homeostasis of multicellular animals requires precise coordination of cell division and differentiation. We performed a genome-wide RNA interference screen in Caenorhabditis elegans to reveal the components of a regulatory network that promotes developmentally programmed cell-cycle quiescence. The 107 identified genes are predicted to constitute regulatory networks that are conserved among higher animals because almost half of the genes are represented by clear human orthologs. Using a series of mutant backgrounds to assess their genetic activities, the RNA interference clones displaying similar properties were clustered to establish potential regulatory relationships within the network. This approach uncovered four distinct genetic pathways controlling cell-cycle entry during intestinal organogenesis. The enhanced phenotypes observed for animals carrying compound mutations attest to the collaboration between distinct mechanisms to ensure strict developmental regulation of cell cycles. Moreover, we characterized ubc-25, a gene encoding an E2 ubiquitin-conjugating enzyme whose human ortholog, UBE2Q2, is deregulated in several cancers. Our genetic analyses suggested that ubc-25 acts in a linear pathway with cul-1/Cul1, in parallel to pathways employing cki-1/p27 and lin-35/pRb to promote cell-cycle quiescence. Further investigation of the potential regulatory mechanism demonstrated that ubc-25 activity negatively regulates CYE-1/cyclin E protein abundance in vivo. Together, our results show that the ubc-25-mediated pathway acts within a complex network that integrates the actions of multiple molecular mechanisms to control cell cycles during development.

Much of our understanding of the function and regulation of the Cdc14 family of dual-specificity phosphatases originates from studies in yeasts. In these unicellular organisms Cdc14 is an important regulator of M-phase events. In contrast, the Caenorhabditis elegans homolog, cdc-14, is not necessary for mitosis, rather it is crucial for G1/S regulation to establish developmental cell-cycle quiescence. Despite the importance of integrating cdc-14 regulation with development, the mechanisms by which this coordination occurs are largely unknown. Here, we demonstrate that several processes conspire to focus the activity of cdc-14. First, the cdc-14 locus can produce at least six protein variants through alternative splicing. We find that a single form, CDC-14C, is the key variant acting during vulva development. Second, CDC-14C expression is limited to a subset of cells, including vulva precursors, through post-transcriptional regulation. Lastly, the CDC-14C subcellular location, and thus its potential interactions with other regulatory proteins, is regulated by nucleocytoplasmic shuttling. We find that the active export of CDC-14C from the nucleus during interphase is dependent on members of the Cyclin D and Crm1 families. We propose that these mechanisms collaborate to restrict the activity of cdc-14 as central components of an evolutionarily conserved regulatory network to coordinate cell-cycle progression with development.

Activation of central chemoreceptors by CO2 increases arterial blood pressure (ABP), sympathetic nerve activity (SNA), and breathing. Experiments using SHRs, a well‐established neurogenic hypertensive model, have shown that the high ABP is associated with elevated SNA and peripheral chemoreflexes, and an impaired baroreflex. We have showed that: 1) SHRs have an age‐dependent increase in CO2 chemoreflex and ABP; 2) the increased CO2 chemoreflex and ABP are measureable in juveniles (P28–50); 3) the enhanced CO2 chemoreflex persists while peripheral chemoreceptors were inhibited by hyperoxia indicating an important role for central chemoreflex in neurogenic hypertension; and 4) blocking orexin receptors with a dual orexin receptor antagonist, Almorexant (Almxt), can normalize the enhanced CO2 chemoreflex and significantly lower high ABP in SHRs. In this study, we evaluated CO2‐activated c‐fos expression in orexin neurons in both hypertensive (SHRs) and normotensive control (WKY) rats, and hypothesized that the enhanced CO2 chemoreflex observed in SHRs is associated with increased number of CO2‐activated c‐fos expressing orexin neurons in the lateral hypothalamic area (LHA). The rats were exposed to 7%CO2 for 1.5hr, and sections of LHA were double stained for c‐fos and orexin‐A. The Stereo Investigator System was used for the cell counts. The results show that in the LHA, SHRs have: 1) more orexin‐containing neurons (~28%), similar as some recent reports, and 2) more CO2‐induced c‐fos and orexin double‐expressing neurons (~71%) than that of age‐matched normotensive WKY rats. We conclude that the enhanced CO2 chemoreflex in SHRs is associated with the overactive orexin system, and modulation of this overactive orexin system and CO2 chemoreflex could be beneficial in treating neurogenic hypertension.Support or Funding InformationNIH HL 28066