Macrophage depletion suppresses sympathetic hyperinnervation following myocardial infarction.

Myocardial infarction induces sympathetic axon sprouting adjacent to the necrotic region, and this has been implicated in the etiology of arrhythmias resulting in sudden cardiac death. Previous studies show that nerve growth factor (NGF) is essential for enhanced post-infarct sympathetic sprouting, but the cell types necessary to supply this neurotrophic protein are unknown. The objective of the present study was to determine whether macrophages, which are known to synthesize NGF, are necessary for post-infarct cardiac sympathetic sprouting. Ovariectomized female rats received left coronary artery ligation or sham operation, followed by intravenous injection of liposomes containing saline vehicle or clodronate, which kills macrophages. Sham-operated myocardium contained some sympathetic axons, few myofibroblasts and T cells and no CD-68-positive macrophages. In rats receiving saline liposomes through 7 days post-ligation, the posterolateral infarct border contained numerous myofibroblasts, macrophages and T cells, and sympathetic innervation was increased twofold. Treatment with clodronate liposomes reduced macrophage numbers by 69%, while myofibroblast area was reduced by 23% and T cell number was unaffected. Clodronate liposome treatment reduced sympathetic axon density to levels comparable to the uninfarcted heart. NGF protein content measured in western blots was reduced to 33% of that present in infarcts where rats received saline-containing liposomes. Tissue morphometry confirmed that NGF immunostaining was dramatically reduced, and this was attributable primarily to reduced macrophage content. These results show that macrophage destruction markedly reduces post-infarction levels of NGF and that the presence of elevated numbers of macrophages is obligatory for development of sympathetic hyperinnervation following myocardial infarction.

Sympathetic hyperinnervation and inflammatory cell NGF synthesis following myocardial infarction in rats.

Sympathetic hyperinnervation occurs in human ventricular tissue after myocardial infarction and may contribute to arrhythmias. Aberrant sympathetic sprouting is associated with elevated nerve growth factor (NGF) in many contexts, including ventricular hyperinnervation. However, it is unclear whether cardiomyocytes or other cell types are responsible for increased NGF synthesis. In this study, left coronary arteries were ligated and ventricular tissue examined in rats 1-28 days post-infarction. Infarct and peri-infarct tissue was essentially devoid of sensory and parasympathetic nerves at all time points. However, areas of increased sympathetic nerve density were observed in the peri-infarct zone between post-ligation days 4-14. Hyperinnervation occurred in regions containing accumulations of macrophages and myofibroblasts. To assess whether these inflammatory cells synthesize NGF, sections were processed for NGF in situ hybridization and immunohistochemistry. Both macrophage1 antigen-positive macrophages and alpha-smooth muscle actin-immunoreactive myofibroblasts expressed NGF in areas where they were closely proximate to sympathetic nerves. To investigate whether NGF produced by peri-infarct cells induces sympathetic outgrowth, we co-cultured adult sympathetic ganglia with peri-infarct explants. Neurite outgrowth from sympathetic ganglia was significantly greater at post-ligation days 7-14 as compared to control tissue. Addition of an NGF function-blocking antibody prevented the increased neurite outgrowth induced by peri-infarct tissue. These findings provide evidence that inflammatory cell NGF synthesis plays a causal role in sympathetic hyperinnervation following myocardial infarction.

Neuronal and nonneuronal quantitative BACE immunocytochemical expression in the entorhinohippocampal and frontal regions in Alzheimer's disease.

In this study, we quantitatively investigated the expression of beta-site amyloid precursor protein cleaving enzyme (BACE) in the entorhinohippocampal and frontal cortex of Alzheimer's disease (AD) and old control subjects. The semiquantitative estimation indicated that the intensity of BACE overall immunoreactivity did not differ significantly between AD and controls, but that a significantly stronger staining was observed in the hippocampal regions CA3-4 compared to other regions in both AD patients and controls. The quantitative estimation confirmed that the number of BACE-positive neuronal profiles was not significantly decreased in AD. However, some degeneration of BACE-positive profiles was attested by the colocalization of neurons expressing BACE and exhibiting neurofibrillary tangles (NFT), as well as by a decrease in the surface area of BACE-positive profiles. In addition, BACE immunocytochemical expression was observed in and around senile plaques (SP), as well as in reactive astrocytes. BACE-immunoreactive astrocytes were localized in the vicinity or close to the plaques and their number was significantly increased in AD entorhinal cortex. The higher amount of beta-amyloid SP and NFT in AD was not correlated with an increase in BACE immunoreactivity. Taken together, these data accent that AD progression does not require an increased neuronal BACE protein level, but suggest an active role of BACE in immunoreactive astrocytes. Moreover, the strong expression in controls and regions less vulnerable to AD puts forward the probable existence of alternate BACE functions.