Robust coupling of angiogenesis and osteogenesis by VEGF-decorated matrices for bone regeneration

Rapid vascularization of clinical-size bone grafts is an unsolved challenge in regenerative medicine. Vascular endothelial growth factor-A (VEGF) is the master regulator of angiogenesis. Its over-expression by genetically modified human osteoprogenitors has been previously evaluated to drive vascularization in osteogenic grafts, but has been observed to cause paradoxical bone loss through excessive osteoclast recruitment. However, during bone development angiogenesis and osteogenesis are physiologically coupled by VEGF expression. Here we investigated whether the mode of VEGF delivery may be a key to recapitulate its physiological function. VEGF activity requires binding to the extracellular matrix, and heterogeneous levels of expression lead to localized microenvironments of excessive dose. Therefore we hypothesized that a homogeneous distribution of matrix-associated factor in the microenvironment may enable efficient coupling of angiogenesis and bone formation. This was achieved by decorating fibrin matrices with a cross-linkable engineered version of VEGF (TG-VEGF) that is released only by enzymatic cleavage by invading cells. In ectopic grafts, both TG-VEGF and VEGF-expressing progenitors similarly improved vascularization within the first week, but efficient bone formation was possible only in the factor-decorated matrices, whereas heterogenous, cell-based VEGF expression caused significant bone loss. In critical-size orthotopic calvaria defects, TG-VEGF effectively improved early vascular invasion, osteoprogenitor survival and differentiation, as well as bone repair compared to both controls and VEGF-expressing progenitors. In conclusion, homogenous distribution of matrix-associated VEGF protein preserves the physiological coupling of angiogenesis and osteogenesis, providing an attractive and clinically applicable strategy to engineer vascularized bone. STATEMENT OF SIGNIFICANCE: The therapeutic regeneration of vascularized bone is an unsolved challenge in regenerative medicine. Stimulation of blood vessel growth by over-expression of VEGF has been associated with paradoxical bone loss, whereas angiogenesis and osteogenesis are physiologically coupled by VEGF during development. Here we found that controlling the distribution of VEGF dose in an osteogenic graft is key to recapitulate its physiological function. In fact, homogeneous decoration of fibrin matrices with engineered VEGF could improve both vascularization and bone formation in orthotopic critical-size defects, dispensing with the need for combined osteogenic factor delivery. VEGF-decorated fibrin matrices provide a readily translatable platform for engineering a controlled microenvironment for bone regeneration.

Pim1 maintains telomere length in mouse cardiomyocytes by inhibiting TGFβ signalling

AIMS

Telomere attrition in cardiomyocytes is associated with decreased contractility, cellular senescence, and up-regulation of proapoptotic transcription factors. Pim1 is a cardioprotective kinase that antagonizes the aging phenotype of cardiomyocytes and delays cellular senescence by maintaining telomere length, but the mechanism remains unknown. Another pathway responsible for regulating telomere length is the transforming growth factor beta (TGFβ) signalling pathway where inhibiting TGFβ signalling maintains telomere length. The relationship between Pim1 and TGFβ has not been explored. This study delineates the mechanism of telomere length regulation by the interplay between Pim1 and components of TGFβ signalling pathways in proliferating A549 cells and post-mitotic cardiomyocytes.

METHODS AND RESULTS

Telomere length was maintained by lentiviral-mediated overexpression of PIM1 and inhibition of TGFβ signalling in A549 cells. Telomere length maintenance was further demonstrated in isolated cardiomyocytes from mice with cardiac-specific overexpression of PIM1 and by pharmacological inhibition of TGFβ signalling. Mechanistically, Pim1 inhibited phosphorylation of Smad2, preventing its translocation into the nucleus and repressing expression of TGFβ pathway genes.

CONCLUSION

Pim1 maintains telomere lengths in cardiomyocytes by inhibiting phosphorylation of the TGFβ pathway downstream effectors Smad2 and Smad3, which prevents repression of telomerase reverse transcriptase. Findings from this study demonstrate a novel mechanism of telomere length maintenance and provide a potential target for preserving cardiac function.

EphrinB2/EphB4 signaling regulates non-sprouting angiogenesis by VEGF

Vascular endothelial growth factor (VEGF) is the master regulator of angiogenesis, whose best-understood mechanism is sprouting. However, therapeutic VEGF delivery to ischemic muscle induces angiogenesis by the alternative process of intussusception, or vascular splitting, whose molecular regulation is essentially unknown. Here, we identify ephrinB2/EphB4 signaling as a key regulator of intussusceptive angiogenesis and its outcome under therapeutically relevant conditions. EphB4 signaling fine-tunes the degree of endothelial proliferation induced by specific VEGF doses during the initial stage of circumferential enlargement of vessels, thereby limiting their size and subsequently enabling successful splitting into normal capillary networks. Mechanistically, EphB4 neither inhibits VEGF-R2 activation by VEGF nor its internalization, but it modulates VEGF-R2 downstream signaling through phospho-ERK1/2. In vivo inhibitor experiments show that ERK1/2 activity is required for EphB4 regulation of VEGF-induced intussusceptive angiogenesis. Lastly, after clinically relevant VEGF gene delivery with adenoviral vectors, pharmacological stimulation of EphB4 normalizes dysfunctional vascular growth in both normoxic and ischemic muscle. These results identify EphB4 as a druggable target to modulate the outcome of VEGF gene delivery and support further investigation of its therapeutic potential.

Cardiac c-Kit Biology Revealed by Inducible Transgenesis

RATIONALE

Biological significance of c-Kit as a cardiac stem cell marker and role(s) of c-Kit+ cells in myocardial development or response to pathological injury remain unresolved because of varied and discrepant findings. Alternative experimental models are required to contextualize and reconcile discordant published observations of cardiac c-Kit myocardial biology and provide meaningful insights regarding clinical relevance of c-Kit signaling for translational cell therapy.

OBJECTIVE

The main objectives of this study are as follows: demonstrating c-Kit myocardial biology through combined studies of both human and murine cardiac cells; advancing understanding of c-Kit myocardial biology through creation and characterization of a novel, inducible transgenic c-Kit reporter mouse model that overcomes limitations inherent to knock-in reporter models; and providing perspective to reconcile disparate viewpoints on c-Kit biology in the myocardium.

METHODS AND RESULTS

In vitro studies confirm a critical role for c-Kit signaling in both cardiomyocytes and cardiac stem cells. Activation of c-Kit receptor promotes cell survival and proliferation in stem cells and cardiomyocytes of either human or murine origin. For creation of the mouse model, the cloned mouse c-Kit promoter drives Histone2B-EGFP (enhanced green fluorescent protein; H2BEGFP) expression in a doxycycline-inducible transgenic reporter line. The combination of c-Kit transgenesis coupled to H2BEGFP readout provides sensitive, specific, inducible, and persistent tracking of c-Kit promoter activation. Tagging efficiency for EGFP+/c-Kit+ cells is similar between our transgenic versus a c-Kit knock-in mouse line, but frequency of c-Kit+ cells in cardiac tissue from the knock-in model is 55% lower than that from our transgenic line. The c-Kit transgenic reporter model reveals intimate association of c-Kit expression with adult myocardial biology. Both cardiac stem cells and a subpopulation of cardiomyocytes express c-Kit in uninjured adult heart, upregulating c-Kit expression in response to pathological stress.

CONCLUSIONS

c-Kit myocardial biology is more complex and varied than previously appreciated or documented, demonstrating validity in multiple points of coexisting yet heretofore seemingly irreconcilable published findings.

Peptidyl-Prolyl Isomerase 1 Regulates Ca2+ Handling by Modulating Sarco(Endo)Plasmic Reticulum Calcium ATPase and Na2+/Ca2+ Exchanger 1 Protein Levels and Function

Background

Aberrant Ca²⁺ handling is a prominent feature of heart failure. Elucidation of the molecular mechanisms responsible for aberrant Ca²⁺ handling is essential for the development of strategies to blunt pathological changes in calcium dynamics. The peptidyl‐prolyl cis‐trans isomerase peptidyl‐prolyl isomerase 1 (Pin1) is a critical mediator of myocardial hypertrophy development and cardiac progenitor cell cycle. However, the influence of Pin1 on calcium cycling regulation has not been explored. On the basis of these findings, the aim of this study is to define Pin1 as a novel modulator of Ca²⁺ handling, with implications for improving myocardial contractility and potential for ameliorating development of heart failure.

Methods and Results

Pin1 gene deletion or pharmacological inhibition delays cytosolic Ca²⁺ decay in isolated cardiomyocytes. Paradoxically, reduced Pin1 activity correlates with increased sarco(endo)plasmic reticulum calcium ATPase (SERCA2a) and Na²⁺/Ca²⁺ exchanger 1 protein levels. However, SERCA2a ATPase activity and calcium reuptake were reduced in sarcoplasmic reticulum membranes isolated from Pin1‐deficient hearts, suggesting that Pin1 influences SERCA2a function. SERCA2a and Na²⁺/Ca²⁺ exchanger 1 associated with Pin1, as revealed by proximity ligation assay in myocardial tissue sections, indicating that regulation of Ca²⁺ handling within cardiomyocytes is likely influenced through Pin1 interaction with SERCA2a and Na²⁺/Ca²⁺ exchanger 1 proteins.

Conclusions

Pin1 serves as a modulator of SERCA2a and Na²⁺/Ca²⁺ exchanger 1 Ca²⁺ handling proteins, with loss of function resulting in impaired cardiomyocyte relaxation, setting the stage for subsequent investigations to assess Pin1 dysregulation and modulation in the progression of heart failure.

Abstract 187: c-Kit Biology Revealed by Two Transgenic Reporter Models

Background: The biological significance of c-Kit as a marker of cardiac stem cells, and role(s) of c-Kit+ cells in myocardial development or in response to pathologic injury remain unresolved due to varied findings among investigators and experimental model systems. Alternative experimental models and approaches are needed to achieve a broader perspective of cardiac c-Kit biology that contextualizes discrepant published observations.

Objectives: Tracking c-Kit expression using transgenesis overcomes limitations inherent to knock-in reporter models. Two novel, inducible transgenic c-Kit reporter models are presented in this study to further elaborate on myocardial c-Kit biology.

Methods: A previously characterized mouse c-Kit promoter segment was engineered to generate a transgenic mouse in which rtTA transactivator is expressed in c-Kit+ cells (c-KitrtTA). c-KitrtTA crossed to Tet-Responsive-Element(TRE)-Histone2B-EGFP or TRE-Cre lines produces the CKH2B and CKCre double transgenic lines, which express doxycycline-inducible H2BEGFP or Cre proteins in c-Kit+ cells. The CKmTmG triple transgenic mouse, arising from CKCre crossed to the ROSAmTmG reporter line, utilizes doxycycline induced recombination to tag c-Kit+ cells irreversibly with membrane bound EGFP. Endogenous c-Kit and transgenic reporter expression was assessed in adult cardiac myocyte and nonmyocyte cells from these mice under resting and cellular stress conditions using immunohistochemistry and flow cytometry.

Results: Coincidence of c-Kit and EGFP is observed in approximately 75% of freshly isolated nonmyocyte cells as detected by flow cytometry. A subpopulation of cardiomyocytes express H2BEGFP or mEGFP in the uninjured, doxycycline treated adult heart. H2BEGFP and c-Kit expression increase in myocytes in response to isoproterenol-induced pathologic stress in vivo and in vitro.

Conclusion: These c-Kit transgenic reporter models provide sensitive, specific, inducible and persistent tracking of c-Kit promoter activation. Results presented here reveal an unexpected role for c-Kit expression in adult cardiomyocytes. Future studies will use both models to investigate c-Kit expression in all cell types during cardiac formation and repair.

VEGF dose regulates vascular stabilization through Semaphorin3A and the Neuropilin-1+ monocyte/TGF-β1 paracrine axis

VEGF is widely investigated for therapeutic angiogenesis, but while short-term delivery is desirable for safety, it is insufficient for new vessel persistence, jeopardizing efficacy. Here, we investigated whether and how VEGF dose regulates nascent vessel stabilization, to identify novel therapeutic targets. Monoclonal populations of transduced myoblasts were used to homogeneously express specific VEGF doses in SCID mouse muscles. VEGF was abrogated after 10 and 17 days by Aflibercept treatment. Vascular stabilization was fastest with low VEGF, but delayed or prevented by higher doses, without affecting pericyte coverage. Rather, VEGF dose-dependently inhibited endothelial Semaphorin3A expression, thereby impairing recruitment of Neuropilin-1-expressing monocytes (NEM), TGF-β1 production and endothelial SMAD2/3 activation. TGF-β1 further initiated a feedback loop stimulating endothelial Semaphorin3A expression, thereby amplifying the stabilizing signals. Blocking experiments showed that NEM recruitment required endogenous Semaphorin3A and that TGF-β1 was necessary to start the Semaphorin3A/NEM axis. Conversely, Semaphorin3A treatment promoted NEM recruitment and vessel stabilization despite high VEGF doses or transient adenoviral delivery. Therefore, VEGF inhibits the endothelial Semaphorin3A/NEM/TGF-β1 paracrine axis and Semaphorin3A treatment accelerates stabilization of VEGF-induced angiogenesis.

Notch activation enhances lineage commitment and protective signaling in cardiac progenitor cells

Phase I clinical trials applying autologous progenitor cells to treat heart failure have yielded promising results; however, improvement in function is modest, indicating a need to enhance cardiac stem cell reparative capacity. Notch signaling plays a crucial role in cardiac development, guiding cell fate decisions that underlie myocyte and vessel differentiation. The Notch pathway is retained in the adult cardiac stem cell niche, where level and duration of Notch signal influence proliferation and differentiation of cardiac progenitors. In this study, Notch signaling promotes growth, survival and differentiation of cardiac progenitor cells into smooth muscle lineages in vitro. Cardiac progenitor cells expressing tamoxifen-regulated intracellular Notch1 (CPCeK) are significantly larger and proliferate more slowly than control cells, exhibit elevated mTORC1 and Akt signaling, and are resistant to oxidative stress. Vascular smooth muscle and cardiomyocyte markers increase in CPCeK and are augmented further upon ligand-mediated induction of Notch signal. Paracrine signals indicative of growth, survival and differentiation increase with Notch activity, while markers of senescence are decreased. Adoptive transfer of CPCeK into infarcted mouse myocardium enhances preservation of cardiac function and reduces infarct size relative to hearts receiving control cells. Greater capillary density and proportion of vascular smooth muscle tissue in CPCeK-treated hearts indicate improved vascularization. Finally, we report a previously undescribed signaling mechanism whereby Notch activation stimulates CPC growth, survival and differentiation via mTORC1 and paracrine factor expression. Taken together, these findings suggest that regulated Notch activation potentiates the reparative capacity of CPCs in the treatment of cardiac disease.

European palliative care guidelines: how well do they meet the needs of people with impaired cognition?

OBJECTIVE

Numbers of people dying with cognitive impairment (intellectual disability (ID), dementia or delirium) are increasing. We aimed to examine a range of European national palliative care guidelines to determine if, and how well, pain detection and management for people dying with impaired cognition are covered.

METHODS

Questionnaires were sent to 14 country representatives of the European Pain and Impaired Cognition (PAIC) network who identified key national palliative care guidelines. Data was collected on guideline content: inclusion of advice on pain management, whether cognitively impaired populations were mentioned, assessment tools and management strategies recommended. Quality of guideline development was assessed with the Appraisal of Guidelines Research and Evaluation (AGREE) instrument.

RESULTS

11 countries identified palliative care guidelines, 10 of which mentioned pain management in general. Of these, seven mentioned cognitive impairment (3 dementia, 2 ID and 4 delirium). Half of guidelines recommended the use of pain tools for people with cognitive impairment; recommended tools were not all validated for the target populations. Guidelines from the UK, the Netherlands and Finland included most information on pain management and detection in impaired cognition. Guidelines from Iceland, Norway and Spain scored most highly on AGREE rating in terms of developmental quality.

CONCLUSIONS

European national palliative care guidelines may not meet the needs of the growing population of people dying with cognitive impairment. New guidelines should consider suggesting the use of observational pain tools for people with cognitive impairment. Better recognition of their needs in palliative care guidelines may drive improvements in care.

Intraperitoneal nebulization of ropivacaine for pain control after laparoscopic cholecystectomy: a double-blind, randomized, placebo-controlled trial

BACKGROUND

Intraperitoneal local anaesthetic nebulization is a relatively novel approach to pain management after laparoscopic surgery. This randomized, double-blind, placebo-controlled trial evaluated the effects of intraperitoneal ropivacaine nebulization on pain control after laparoscopic cholecystectomy.

METHODS

Patients undergoing laparoscopic cholecystectomy were randomized to receive intraperitoneal nebulization of ropivacaine 1% (3 ml) before surgical dissection and normal saline 3 ml at the end of surgery (preoperative nebulization group); intraperitoneal nebulization of normal saline 3 ml before surgical dissection and ropivacaine 1% (3 ml) at the end of surgery (postoperative nebulization group); or intraperitoneal nebulization of normal saline 3 ml before surgical dissection and at the end of surgery (placebo group). Intraperitoneal nebulization of ropivacaine or saline was performed using the Aeroneb Pro(®) device. Anaesthetic and surgical techniques were standardized. The degree of pain on deep breath or movement, incidence of shoulder pain, morphine consumption, and postoperative nausea and vomiting were collected in the post-anaesthesia care unit and at 6, 24, and 48 h after surgery.

RESULTS

Compared with placebo, ropivacaine nebulization significantly reduced postoperative pain (-33%; Cohen's d 0.64), referred shoulder pain (absolute reduction -98%), morphine requirements (-41% to -56% Cohen's d 1.16), and time to unassisted walking (up to -44% Cohen's d 0.9) (P<0.01). There were no differences in pain scores between ropivacaine nebulization groups.

CONCLUSIONS

Ropivacaine nebulization before or after surgery reduced postoperative pain and referred shoulder pain after laparoscopic cholecystectomy. Furthermore, ropivacaine nebulization reduced morphine requirements and allowed earlier mobility.