Evidence supporting the functionality of Smoothened (SMO), an essential transducer in most pathways engaged by Hedgehog (Hh), as a Gi-coupled receptor contrasts with the lack of an apparently consistent requirement for Gi in Hh signal transduction. In the present study, we sought to evaluate the role of SMO-Gi coupling in fibroblast migration induced by Sonic Hedgehog (Shh). Our results demonstrate an absolute requirement for Gi in Shh-induced fibroblast migration. We found that Shh acutely stimulates the small Rho GTPases Rac1 and RhoA via SMO through a Gi protein- and PI3K-dependent mechanism, and that these are required for cell migration. These responses were independent of transcription by Gli and of the C-terminal domain of SMO, as we show using a combination of molecular and genetic tools. Our findings provide a mechanistic model for fibroblast migration in response to Shh and underscore the role of SMO-Gi coupling in non-canonical Hh signaling.

The vertebrate Hedgehog (Hh) pathway has essential functions during development and tissue homeostasis during normal physiology while its dysregulation is a common theme in cancer. The Hh ligands (Sonic, Indian, and Desert Hh), bind to the receptors Patched1 and 2, resulting in inhibition of their repressive effect on Smoothened (Smo). Smo is a 7-transmembrane protein, which was only recently proved to function as a GPCR with specificity toward Gi. In addition to Gi activation, Smo signals via its C-tail to inhibit Suppressor of Fused (Sufu), resulting in stabilization and activation of the Gli family of transcription factors, which execute a transcriptional response to the so-called “canonical Hh signaling”. In this presentation we illustrate two outcomes of Hh signaling that are independent of Gli transcriptional activity and, thus, are defined as “non-canonical”. One outcome is dependent on Smo coupling to Gi proteins and exerts changes in the actin cytoskeleton via stimulation of RhoA and Rac1. These cytoskeletal changes promote migration in fibroblasts and tubulogenesis in endothelial cells. The other non-canonical Hh pathway is independent of Smo, and consists of inhibition of Patched1-induced cell death.

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Rationale: Cancer therapy can be associated with short- and long-term cardiac dysfunction. Cancer patients often exhibit therapy-related clonal hematopoiesis (t-CH), an aggressive form of clonal hematopoiesis that can result from somatic mutations in genes encoding regulators of the DNA-damage response (DDR) pathway. Gain-of-function mutations in exon 6 the protein phosphatase Mg2+/Mn2+ dependent 1D (PPM1D) gene are the most frequently mutated DDR gene associated with t-CH. Whether t-CH can contribute to cardiac dysfunction is unknown. Objective: We evaluated the causal and mechanistic relationships between Ppm1d-mediated t-CH and non-ischemic heart failure in an experimental system. Methods and Results: To test whether gain-of-function hematopoietic cell mutations in Ppm1d can increase the susceptibility to cardiac stress, we evaluated cardiac dysfunction in a mouse model where clonal hematopoiesis-associated mutations in exon 6 of Ppm1d were produced by CRISPR-Cas9 technology. Mice transplanted with hematopoietic stem cells containing the mutated Ppm1d gene exhibited augmented cardiac remodeling following the continuous infusion of angiotensin II (AngII). Ppm1d-mutant macrophages were impaired in DDR pathway activation and displayed greater DNA damage, higher reactive oxygen species generation and an augmented proinflammatory profile with elevations in IL-1β and IL-18. The administration of an NLRP3 inflammasome inhibitor to mice reversed the cardiac phenotype induced by the Ppm1d-mutated hematopoietic stem cells under conditions of AngII-induced stress. Conclusions: A mouse model of Ppm1d-mediated t-CH was more susceptible to cardiac stress. Mechanistically, disruption of the DDR pathway led to elevations in inflammatory cytokine production, and the NLRP3 inflammasome was shown to be essential for this augmented cardiac stress response. These data indicate that t-CH involving activating mutations in PPM1D can contribute to the cardiac dysfunction observed in cancer survivors, and that anti-inflammatory therapy may have utility in treating this condition.

The cardiovascular effects and pharmacokinetics of carvedilol were assessed in spontaneously hypertensive (SH) and Wistar Kyoto (WKY) animals with special focus on short-term blood pressure variability (BPV). Male SH and WKY rats were acutely treated with vehicle or carvedilol 1 or 5 mg kg(-1) (i.v.), and effects on blood pressure (BP), heart rate (HR) and BPV were recorded. Plasma pharmacokinetics of R- and S-carvedilol was studied by traditional blood sampling. Relationship between carvedilol concentrations and their hypotensive and bradycardic effects was established by pharmacokinetic-pharmacodynamic (PK-PD) modelling. Short-term BPV was assessed by standard deviation of BP recording. Vascular sympatholytic activity of carvedilol was studied by estimation of drug effects on ratio between low frequency (LF) and high frequency (HF) BPV (LF/HF ratio). Although pharmacokinetic properties of carvedilol remained mainly unaffected in SH rats with regard to WKY rats, hypertensive animals showed a reduction in drug clearance of R- and S-carvedilol after administration of 1 mg kg(-1) compared with WKY rats. PK-PD analysis of HR changes induced by S-carvedilol showed a greater maximal bradycardic response to carvedilol in SH rats (E (max), -27.6 ± 3.9%; p < 0.05) compared with WKY group (E (max), -13.4 ± 2.5%). SH rats showed a greater hypotensive effect of racemic carvedilol (E (max), -45.5 ± 5.0%; p < 0.05) with regard to WKY group (E (max), -17.9 ± 4.5%). Carvedilol induced a greater reduction of LF/HF ratio in SH rats compared with WKY rats. Short-term BPV was markedly reduced by carvedilol in WKY and SH rats. In conclusion, as a consequence of an enhanced bradycardic response and a greater vascular sympatholytic activity, carvedilol exerts a greater hypotensive response in SH rats compared with WKY animals and dramatically reduces short-term BPV.

An increase in blood pressure variability (BPV) contributes to the development of target organ damage associated with hypertension. Treatment with conventional β-blockers, such as atenolol, has been associated with an increase in BPV; however, the extrapolation of these results to third generation β-blockers with pleiotropic effects seems to be inappropriate. The cardiovascular effects of third generation β-blockers, carvedilol and nebivolol, were assessed in sinoaortic-denervated rats (SAD) and compared with the second generation β-blocker atenolol and the calcium channel blocker verapamil, with a special focus on short-term BPV. Male SAD rats were acutely treated with carvedilol, nebivolol, atenolol or verapamil at two different doses, and the effects on blood pressure and BPV were recorded. Short-term BPV was assessed by the s.d. of BP recordings. Beat-to-beat BPV was studied using spectral analysis to assess the vascular sympatholytic activity of carvedilol and nebivolol by estimating the effects of these drugs on the ratio of low frequency (LF) to high frequency (HF) BPV (LF/HF ratio). Nebivolol, carvedilol and the calcium channel blocker verapamil significantly attenuated short-term BPV at both doses in SAD animals, and there were no differences between the drugs. Conversely, atenolol did not modify baseline s.d. values at either dose. Carvedilol and nebivolol significantly reduced the LF/HF ratio in SAD rats compared with the effects of atenolol and verapamil, suggesting the ability of the third generation β-blockers to reduce vascular sympathetic activity. In conclusion, third generation β-blockers induce a marked reduction in short-term BPV in SAD rats compared to atenolol. Moreover, the ability of carvedilol and nebivolol to reduce short-term BPV in SAD rats is equivalent to that of verapamil, suggesting that these β-blockers may have an additional beneficial effect through their control of short-term variability to a similar extent to calcium channel blockers.