The present study aimed to determine whether peripheral and/or central chemoreflex function is altered in chronic heart failure (CHF) and whether altered chemoreflex function contributes to sympathetic activation in CHF. A rabbit model of pacing-induced CHF was employed. The development of CHF (3-4 wk of pacing) was characterized by an enlarged heart, an attenuated contractility, and an elevated central venous pressure. Renal sympathetic nerve activity (RSNA) and minute volume (MV) of ventilation in response to stimulation of peripheral chemoreceptors by isocapnic/hypoxic gases were measured in the conscious state. It was found that the baseline RSNA at normoxia was higher in CHF rabbits than in sham rabbits (35. 00 +/- 4.03 vs. 20.75 +/- 2.87% of maximum, P < 0.05). Moreover, the magnitudes of changes in RSNA and MV in response to stimulation of the peripheral chemoreceptors and the slopes of RSNA-arterial PO2 and MV-arterial PO2 curves were greater in CHF than in sham rabbits. Inhibition of the peripheral chemoreceptors by inhalation of 100% O2 decreased RSNA in CHF but not in sham rabbits. The central chemoreflex function, as evaluated by the responses of RSNA and MV to hyperoxic/hypercapnic gases, was not different between sham and CHF rabbits. These data suggest that an enhancement of the peripheral chemoreflex occurs in the rabbit model of pacing-induced CHF and that the enhanced peripheral chemoreflex function contributes to the sympathetic activation in the CHF state.

An enhanced peripheral chemoreflex has been documented in patients with chronic heart failure (CHF). This study aimed to examine the characteristics of carotid body (CB) chemoreceptors in response to isocapnic hypoxia in a rabbit model of pacing-induced CHF and to evaluate the possible role that nitric oxide (NO) plays in the altered characteristics. The chemosensitive characteristics of the CB were evaluated by recording single-unit activity from the carotid sinus nerve in both an intact and a vascularly isolated preparation. It was found that the baseline discharge under normoxia (intact preparation: arterial PO2 90-95 Torr; isolated preparation: PO2 100-110 Torr) and the chemosensitivity in response to graded hypoxia (PO2 40-70 Torr) were enhanced in CHF vs. sham rabbits. These alterations were independent of the CB preparations (intact vs. isolated). NO synthase inhibition by Nomega-nitro-L-arginine increased the baseline discharge and the chemosensitivity in the intact preparation, whereas L-arginine (10(-5) M) inhibited the baseline discharge and the chemosensitivity in the isolated preparation in sham but not in CHF rabbits. S-nitroso-N-acetylpenicillamine, an NO donor, inhibited the baseline discharge and the chemosensitivity in both CB preparations in CHF rabbits but only in the isolated preparation in sham rabbits. The amount of NO produced in vitro by the CB under normoxia was less in CHF rabbits than in sham rabbits (P < 0.05). NO synthase-positive varicosities of nerve fibers within the CB were less in CHF rabbits than in sham rabbits (P < 0.05). These data indicate that an enhanced input from CB occurs in the rabbit model of pacing-induced CHF and that an impairment of NO production may contribute to this alteration.

Background: Platelet-rich plasma (PRP) provides a nonsurgical approach for treating osteoarthritis (OA). Exosomes that play vital roles in intercellular communication have been studied extensively. Here, we investigated the therapeutic potential and molecular mechanism of exosomes derived from PRP (PRP-Exos) in alleviating OA.Methods: Exosomes derived from PRP(PRP-Exos) were isolated and purified using the exoEasy Maxi Kit and then identified and analyzed. Primary rabbit chondrocytes were isolated and treated with interleukin 1 beta (IL-1β) to establish the OA model in vitro. Proliferation, migration, and apoptosis assays were measured and compared between PRP-Exos and activated PRP (PRP-As) to evaluate the therapeutic effects on OA. The mechanism involving the Wnt/β-catenin signaling pathway was investigated by Western blot analysis. In vivo, we established animal knee OA model by surgery to compare the therapeutic effect of PRP-Exos and PRP-As. Results:We successfully isolated and purified exosomes from PRP using the exoEasy Maxi Kit. We also isolated and identified chondrocytes from the New Zealand white rabbit and established the IL-1β-induced OA model; meanwhile, PRP-Exos and PRP-As both inhibited the release of tumor necrosis factor-α(TNF-α) and there was no statistically significant difference between the two. In proliferation, migration, scratch assay, the promoting effect of PRP-Exos was significantly more better than PRP-As. Furthermore, PRP-Exos could significantly decreased apoptotic rate of OA chondrocyte compared with PRP-As. In Western blot analysis, the expression of β-catenin, and RUNX2, Wnt5a were increased in IL-1β-treated chondrocytes, but PRP-Exos and PRP-As could both reverse these changes, and the reversal effect of the former was better than the latter. In vivo, we found that both PRP-Exos and PRP-As displayed the progression of OA, and the effect of PRP-Exos was obviously better than PRP-As by chondrocyte count and Osteoarthritis Research Society International (OARSI) scoring system. Conclusion: The therapeutic effects of PRP-Exos on OA were similar or better compared with those of PRP-As in vitro or in vivo. PRP-Exos acting as carriers containing growth factors derived from PRP present a novel therapy for OA by activating the Wnt/β-catenin signaling pathway.

We have previously demonstrated that the serine/threonine protein phosphatase-1 (PP-1) plays an important role in promoting cell survival. However, the molecular mechanisms by which PP-1 promotes survival remain largely unknown. In the present study, we provide evidence to show that PP-1 can directly dephosphorylate a master regulator of apoptosis, p53, to negatively modulate its transcriptional and apoptotic activities, and thus to promote cell survival. As a transcriptional factor, the function of p53 can be greatly regulated by phosphorylation and dephosphorylation. While the kinases responsible for phosphorylation of the 17 serine/threonine sites have been identified, the dephosphorylation of these sites remains largely unknown. In the present study, we demonstrate that PP-1 can dephosphorylate p53 at Ser-15 and Ser-37 through co-immunoprecipitation, in vitro and in vivo dephosphorylation assays, overexpression and silence of the gene encoding the catalytic subunit for PP-1. We further show that mutations mimicking constitutive dephosphorylation or phosphorylation of p53 at these sites attenuate or enhance its transcriptional activity, respectively. As a result of the changed p53 activity, expression of the downstream apoptosis-related genes such as bcl-2 and bax is accordingly altered and the apoptotic events are either largely abrogated or enhanced. Thus, our results demonstrate that PP-1 directly dephosphorylates p53, and dephosphorylation of p53 has as important impact on its functions as phosphorylation does. In addition, our results reveal that one of the molecular mechanisms by which PP-1 promotes cell survival is to dephosphorylate p53, and thus negatively regulate p53-dependent death pathway.