Factor H's Control of Complement Activation Emerges as a Significant and Promising Therapeutic Target for Alzheimer's Disease Treatment.

The complement is a component of the innate immune system designed to fight infections and tissue- or age-related damages. Complement activation creates an inflammatory microenvironment, which enhances cell death. Excessive complement inflammatory activity has been linked to alterations in the structure and functions of the blood-brain barrier, contributing to a poor prognosis for Alzheimer's disease (AD). In the AD preclinical phase, individuals are often clinically asymptomatic despite evidence of AD neuropathology coupled with heightened inflammation. Considering the involvement of the complement system in the risk of developing AD, we hypothesize that inhibiting complement activation could reduce this inflammatory period observed even before clinical signs, thereby slowing down the onset/progression of AD. To validate our hypothesis, we injected complement inhibitor factor H into the brain of APP/PS1 AD mice at early or late stages of this pathology. Our results showed that the injection of factor H had effects on both the onset and progression of AD by reducing proinflammatory IL6, TNF-α, IL1ß, MAC and amyloid beta levels. This reduction was associated with an increase in VGLUT1 and Psd95 synaptic transmission in the hippocampal region, leading to an improvement in cognitive functions. This study invites a reconsideration of factor H's therapeutic potential for AD treatment.

Thrombosis in the Coronary Microvasculature Impairs Cardiac Relaxation and Induces Diastolic Dysfunction.

BACKGROUND: Heart failure with preserved ejection fraction is proposed to be caused by endothelial dysfunction in cardiac microvessels. Our goal was to identify molecular and cellular mechanisms underlying the development of cardiac microvessel disease and diastolic dysfunction in the setting of type 2 diabetes. METHODS: We used Leprdb/db (leptin receptor-deficient) female mice as a model of type 2 diabetes and heart failure with preserved ejection fraction and identified Hhipl1 (hedgehog interacting protein-like 1), which encodes for a decoy receptor for HH (hedgehog) ligands as a gene upregulated in the cardiac vascular fraction of diseased mice. RESULTS: We then used Dhh (desert HH)-deficient mice to investigate the functional consequences of impaired HH signaling in the adult heart. We found that Dhh-deficient mice displayed increased end-diastolic pressure while left ventricular ejection fraction was comparable to that of control mice. This phenotype was associated with a reduced exercise tolerance in the treadmill test, suggesting that Dhh-deficient mice do present heart failure. At molecular and cellular levels, impaired cardiac relaxation in DhhECKO mice was associated with a significantly decreased PLN (phospholamban) phosphorylation on Thr17 (threonine 17) and an alteration of sarcomeric shortening ex vivo. Besides, as expected, Dhh-deficient mice exhibited phenotypic changes in their cardiac microvessels including a prominent prothrombotic phenotype. Importantly, aspirin therapy prevented the occurrence of both diastolic dysfunction and exercise intolerance in these mice. To confirm the critical role of thrombosis in the pathophysiology of diastolic dysfunction, we verified Leprdb/db also displays increased cardiac microvessel thrombosis. Moreover, consistently, with Dhh-deficient mice, we found that aspirin treatment decreased end-diastolic pressure and improved exercise tolerance in Leprdb/db mice. CONCLUSIONS: Altogether, these results demonstrate that microvessel thrombosis may participate in the pathophysiology of heart failure with preserved ejection fraction.

Partial Mural Cell Ablation Disrupts Coronary Vasculature Integrity and Induces Systolic Dysfunction.

Background Although the critical role of pericytes in maintaining vascular integrity has been extensively demonstrated in the brain and the retina, little is known about their role in the heart. We aim to investigate structural and functional consequences of partial pericyte depletion (≈60%) in the heart of adult mice. Methods and Results To deplete pericytes in adult mice, we used platelet-derived growth factor receptor ß-Cre/ERT2; RosaDTA mice and compared their phenotype with that of control mice (RosaDTA) chosen among their littermates. Cardiac function was assessed via echocardiography and left ventricular catheterization 1 month after the first tamoxifen injection. We found mice depleted with pericytes had a reduced left ventricular ejection fraction and an increased end-diastolic pressure, demonstrating both systolic and diastolic dysfunction. Consistently, mice depleted with pericytes presented a decreased left ventricular contractility and an increased left ventricular relaxation time (dP/dtmin). At the tissue level, mice depleted of pericytes displayed increased coronary endothelium leakage and activation, which was associated with increased CD45+ cell infiltration. Consistent with systolic dysfunction, pericyte depletion was associated with an increased expression of myosin heavy chain 7 and decreased expression of ATPase sarcoplasmic/endoplasmic reticulum Ca2+ transporting 2 and connexin 43. More important, coculture assays demonstrated, for the first time, that the decreased expression of connexin 43 is likely attributable to a direct effect of pericytes on cardiomyocytes. Besides, this study reveals that cardiac pericytes may undergo strong remodeling on injury. Conclusions Cardiac pericyte depletion induces both systolic and diastolic dysfunction, suggesting that pericyte dysfunction may contribute to the occurrence of cardiac diseases.

Ephrin-B1 regulates the adult diastolic function through a late postnatal maturation of cardiomyocyte surface crests.

The rod-shaped adult cardiomyocyte (CM) harbors a unique architecture of its lateral surface with periodic crests, relying on the presence of subsarcolemmal mitochondria (SSM) with unknown role. Here, we investigated the development and functional role of CM crests during the postnatal period. We found in rodents that CM crest maturation occurs late between postnatal day 20 (P20) and P60 through both SSM biogenesis, swelling and crest-crest lateral interactions between adjacent CM, promoting tissue compaction. At the functional level, we showed that the P20-P60 period is dedicated to the improvement of relaxation. Interestingly, crest maturation specifically contributes to an atypical CM hypertrophy of its short axis, without myofibril addition, but relying on CM lateral stretching. Mechanistically, using constitutive and conditional CM-specific knock-out mice, we identified ephrin-B1, a lateral membrane stabilizer, as a molecular determinant of P20-P60 crest maturation, governing both the CM lateral stretch and the diastolic function, thus highly suggesting a link between crest maturity and diastole. Remarkably, while young adult CM-specific Efnb1 KO mice essentially exhibit an impairment of the ventricular diastole with preserved ejection fraction and exercise intolerance, they progressively switch toward systolic heart failure with 100% KO mice dying after 13 months, indicative of a critical role of CM-ephrin-B1 in the adult heart function. This study highlights the molecular determinants and the biological implication of a new late P20-P60 postnatal developmental stage of the heart in rodents during which, in part, ephrin-B1 specifically regulates the maturation of the CM surface crests and of the diastolic function.

Exact relevance of bone marrow cells in the healing process after myocardial infarction: analysis with a murine model of bone marrow cell transplantation.

BACKGROUND: Cellular cardiomyoplasty has created new possibilities in cardiac regeneration. Several cell types can be used in the procedure, such as skeletal myoblasts and bone marrow cells. Recent publications have suggested that bone marrow cells may be excellent candidates due to their pluripotency, but their actual role in cardiac regeneration is unknown. OBJECTIVE: To evaluate the exact physiological role of bone marrow cells in the healing process after myocardial infarction. METHODS: A mouse bone marrow cell transplantation model was used in which transplanted cells were easily detectable by immunohistochemistry. Chimeric mice were subjected to myocardial infarction by ligation of the left descending coronary artery. After one month, the mice were sacrificed and the scars were analyzed. RESULTS: Transplanted bone marrow cells were detected in the scars and these cells seemed able to transdifferentiate into endothelial cells, but no transdifferentiation into cardiomyocytes occurred. This mechanism of regeneration was dismissed because only 2% of the vessels in the scars were positive for transplanted cells. CONCLUSIONS: Bone marrow cells might be involved in myocardial healing, but this physiological mechanism is insufficient to allow correct regeneration.

[Study of postmyocardial infarction scar-formation mechanisms: advantage of an experimental myocardial infarction model in mice]. / Etude des mécanismes de cicatrisation après infarctus du myocarde: intérêt d'un modèle expérimental d'infarctus du myocarde chez la souris.

Myocardial infarction involves scar-formation mechanisms in which inflammation, proliferation, cell differentiation, apoptosis and angiogenesis all play a role. Better knowledge of the scar-formation process would be helpful in developing new therapies. The authors have generated a mouse model for infarction because its possible application in transgenic mice would allow the role of target genes in postinfarction scar-formation mechanisms to be studied. An infarction is caused by ligating the descending branch of the left coronary artery. At various times after ligation, the mice are sacrificed to determine the size of the infarction, left ventricular function and the overall myocardial scar-formation process. Early mortality was 10%. Between the fourth and sixth day postsurgery, 25% of mice died of a ruptured, infarcted left ventricle. The size of the infarctions diminished with time, while the surface of the left ventricle increased. In hemodynamics, 15 and 30 days after infarction, left ventricle telediastolic pressure was higher, telesystolic pressure was lower and contractility in indexes had collapsed. After an inflammatory phase in which polynuclear neutrophils colonized the scar, granulation tissue set in with a proliferation of myofibroblasts and growth of new blood vessels. These cells disappeared from the scar gradually, leaving behind a matrix rich in collagen and devoid of any contractile properties. The authors have characterized a murine model of myocardial infarction, with applications in transgenic mice and in view of establishing new agents in postmyocardial infarction repair.

Repair of myocardial infarction by epicardial deposition of bone-marrow-cell-coated muscle patch in a murine model.

BACKGROUND: Myocardial infarction results in irreversible myocyte loss. In a murine model, we tested the feasibility of a novel repair technique combining bone marrow cell (BMC) transplantation and cardiomyoplasty. METHODS: Myocardial infarction was induced cryogenically in backcrossed ROSA 26 transgenic x C57BL/6J mice (n = 75). Thirty days later, surviving mice (n = 69) were randomized to sham treatment (rethoracotomy only; n = 11), patch only treatment (n = 29), or patch + BMC treatment (n = 29). Abdominal muscle patches were harvested from donor littermates not expressing the beta-galactosidase reporter gene and sutured on the epicardium directly above the infarct zone. Patch only-treated mice received uncoated patches. Patch + BMC-treated mice received patches coated with 5 x 10(6) beta-galactosidase-expressing BMCs embedded in a collagen-rich three-dimensional matrix. RESULTS: Mortality rate was 52% after muscle patch implantation. Bone marrow cells were able to migrate from muscle patch into the infarct zone, as demonstrated by beta-galactosidase immunostaining, and ultimately constituted 8% of all cells in scar tissue (mean +/- standard deviation, 219 +/- 111/mm2). Angiogenesis and cell survival in the scar were improved by patch + BMC treatment. Left ventricular geometry and cardiac function were improved by patch treatment, with or without BMC, although the effects were stronger after patch + BMC treatment. CONCLUSIONS: Epicardial deposition of a BMC-coated muscle patch is a promising approach to restoring cardiac function after myocardial infarction.

Reduction of infarct size and prevention of cardiac rupture in transgenic mice overexpressing FrzA.

BACKGROUND: FrzA/sFRP-1, a secreted, frizzled-related protein and antagonist for the wnt/frizzled pathway, is expressed in the heart and vessels during mouse embryogenesis and adulthood. FrzA is involved in cell cycle control of vascular cells and angiogenesis. We assessed the hypothesis that FrzA could control the healing process after myocardial infarction (MI). METHODS AND RESULTS: We demonstrated an upregulation of sFRP-1 and distinct wnt and fz member expression after MI. We established transgenic (Tg) mice that overexpress FrzA under a cytomegalovirus promoter and developed a model of MI by coronary artery ligation. FrzA reduced cardiac rupture after MI in Tg (6.5% versus 26.4% in controls; n=165, P<0.01). MI was smaller in Tg at each time point (18+/-10.8% of left ventricular circumference versus 30+/-14.2% in controls at day 30; P<0.001). Similar results were found in cryolesion-induced MI. Cardiac function was improved in Tg mice (3800+/-370 mm Hg/s dP/dtmax versus 2800+/-840 in controls; -2800+/-440 dP/dtmin versus -1800+/-211 in controls at day 15; P<0.001). Early leukocyte infiltration had decreased in Tg mice during the first week. Apoptotic index was decreased by 50% in Tg mice at day 7. Matrix metalloproteinase-2 and -9 activity was reduced in Tg mice at day 4, and collagen deposition in the scar was increased in Tg mice. Capillary density in the scar was higher in Tg mice (290+/-103 vessels/mm2 versus 104+/-43 in controls at day 15; P<0.001). Vessels were more muscularized, and mean lumen area was 3-fold higher in Tg animals. CONCLUSIONS: Overexpression of FrzA, through direct or indirect interaction with different phases of infarct healing, reduced infarct size and improved cardiac function.

Assessment of Left Ventricular Area at Risk by Myocardial Contrast Two-Dimensional Echocardiography: An Evaluation of a New Animal Model.

BACKGROUND: New echocardiographic contrast agents are commonly tested in the dog model. However, this species has a number of drawbacks, including difficulties in experimentation, cost, and ethical considerations. The rabbit has a number of advantages due to its relative simple coronary circulation. The present study was designed to evaluate the rabbit model for determination of areas of risk (ARs) by contrast echocardiography. METHODS: Eight rabbits were intubated and mechanically ventilated after occlusion of the left coronary artery with a ligature. The transducer (operating at 7.5 MHz) was positioned on the right ventricle through a right thoracotomy. The images were obtained after intra-aortic injection of 1 ml of Albunex, followed by 3 ml of dye (Blue Uniperse) for histological analysis postmortem. The ARs were obtained after circumscription of the various echocardiographic and histological images. RESULTS: Excellent echocardiographic images were obtained, largely due to the hemodynamic stability of the rabbit to ischemia. Echocardiographic ventricular areas, absolute AR, and relative AR correlated closely with postmortem data (r = 0.86, 0.94, and 0.94, respectively). The measurements were highly reproducible with low variability. CONCLUSIONS: The rabbit model shows promise for study by contrast echocardiography of myocardium subjected to ischemia. This method for determination of ARs was validated against postmortem findings. The method also should be of value in the evaluation of reperfusion.