Perivascular Macrophages Regulate Blood Flow Following Tissue Damage

Rationale: Ischemic injuries remain a leading cause of mortality and morbidity worldwide, and restoration of functional blood perfusion is vital to limit tissue damage and support healing. Objective: To reveal a novel role of macrophages in reestablishment of functional tissue perfusion following ischemic injury that can be targeted to improve tissue restoration. Methods and Results: Using intravital microscopy of ischemic hind limb muscle in mice, and confocal microscopy of human tissues from amputated legs, we found that macrophages accumulated perivascularly in ischemic muscles, where they expressed high levels of iNOS. Genetic depletion of iNOS specifically in macrophages (Cx3cr1-CreERT2;Nos2fl/fl or LysM-Cre;Nos2fl/fl) did not affect vascular architecture but highly compromised blood flow regulation in ischemic but not healthy muscle, which resulted in aggravated ischemic damage. Thus, the ability to upregulate blood flow was shifted from eNOS (endothelial)-dependence in healthy muscles to completely rely on macrophage-derived iNOS during ischemia. Macrophages in ischemic muscles expressed high levels of CXCR4 and CCR2, and local overexpression by DNA plasmids encoding the corresponding chemokines CXCL12 or CCL2 increased macrophage numbers, while CXCL12 but not CCL2 induced their perivascular positioning. As a result, CXCL12-overexpression increased the number of perfused blood vessels in the ischemic muscles, improved functional muscle perfusion in a macrophage-iNOS-dependent manner, and ultimately restored limb function. Conclusions: This study establishes a new function for macrophages during tissue repair, as they regulate blood flow through the release of iNOS-produced NO. Further, we demonstrate that macrophages can be therapeutically targeted to improve blood flow regulation and functional recovery of ischemic tissues.

Electrically stimulated hind limb muscle contractions increase adult hippocampal astrogliogenesis but not neurogenesis or behavioral performance in male C57BL/6J mice

Regular exercise is crucial for maintaining cognitive health throughout life. Recent evidence suggests muscle contractions during exercise release factors into the blood which cross into the brain and stimulate adult hippocampal neurogenesis. However, no study has tested whether muscle contractions alone are sufficient to increase adult hippocampal neurogenesis and improve behavioral performance. Adult male, C57BL/6J mice were anesthetized and exposed to bilateral hind limb muscle contractions (both concentric and eccentric) via electrical stimulation (e-stim) of the sciatic nerve twice a week for 8 weeks. Each session lasted approximately 20 min and consisted of a total of 40 muscle contractions. The control group was treated similarly except without e-stim (sham). Acute neuronal activation of the dentate gyrus (DG) using cFos immunohistochemistry was measured as a negative control to confirm that the muscle contractions did not activate the hippocampus, and in agreement, no DG activation was observed. Relative to sham, e-stim training increased DG volume by approximately 10% and astrogliogenesis by 75%, but no difference in neurogenesis was detected and no improvement in behavioral performance was observed. E-stim also increased astrogliogenesis in CA1/CA2 hippocampal subfields but not in the cortex. Results demonstrate that muscle contractions alone, in absence of DG activation, are sufficient to increase adult hippocampal astrogliogenesis, but not neurogenesis or behavioral performance in mice.

eNOS Uncoupling: A Therapeutic Target For Ischemic Foot of Diabetic Rat

Aim To determine the relationship between eNOS uncoupling and diabetic ischemic foot and whether reversing eNOS uncoupling by Dihydrofolate reductase (DHFR) transfection or folic acid (FA) supplementation can be beneficiary in diabetic ischemic foot. Methods The bilateral common iliac artery of diabetic rats were ligated to establish the diabetic ischemic foot animal model. DHFR transfection was implemented via femoral artery and muscle injection of in vivo transfection reagent mixture (GenEscortIII) every 4 days during the 2 weeks intervention. The color doppler flow imaging (CDFI) of femoral artery for RI measurement, triceps and quadriceps structure and histology, eNOS coupling status, DHFR expression level, superoxide, peroxynitrite (ONOO– ) and nitric oxide (NO) production in the presence or absence of L-NAME (eNOS inhibitor) were examined among wild type rats (WT), diabetic sham rats (DM), rats of diabetic ischemic foot (DF) or DF with DHFR transfection (DFT) or DF with FA supplementation (DFF). Results Dihydroethidium (DHE) fluorescence, as an index of superoxide production was enhanced in the femoral arteries of diabetic rats and even more in those of ischemic foot from diabetic rats. However, the DHE fluorescence was diminished in the presence of L-NAME suggesting eNOS uncoupling is the source of superoxide overproduction which further led to increased peroxynitrite production and decreased NO. bioavailability. Subsequently, the hind limb muscle became atrophic and the local collateral circulation was defective due to endothelial dysfunction related to eNOS uncoupling. However, all of the above and hemodynamic index (RI) of femoral artery were resumed via restoration of DHFR protein expression by folic acid treatment or DHFR transfection. Conclusions eNOS uncoupling is involved in diabetic ischemic foot due to DHFR suppression. DHFR restoration can reverse eNOS uncoupling and resume the endothelial dysfunction and pathological changes (increased vasculature resistance, hind limb muscle atrophy and defective collateral circulation) associated with eNOS uncoupling in diabetic ischemic foot. All of which enlightens a novel therapeutic strategy for future diabetic ischemic foot treatments.

Robust Central Nervous System Pathology in Transgenic Mice following Peripheral Injection of α-Synuclein Fibrils

ABSTRACT Misfolded α-synuclein (αS) is hypothesized to spread throughout the central nervous system (CNS) by neuronal connectivity leading to widespread pathology. Increasing evidence indicates that it also has the potential to invade the CNS via peripheral nerves in a prion-like manner. On the basis of the effectiveness following peripheral routes of prion administration, we extend our previous studies of CNS neuroinvasion in M83 αS transgenic mice following hind limb muscle (intramuscular [i.m.]) injection of αS fibrils by comparing various peripheral sites of inoculations with different αS protein preparations. Following intravenous injection in the tail veins of homozygous M83 transgenic (M83+/+) mice, robust αS pathology was observed in the CNS without the development of motor impairments within the time frame examined. Intraperitoneal (i.p.) injections of αS fibrils in hemizygous M83 transgenic (M83+/−) mice resulted in CNS αS pathology associated with paralysis. Interestingly, injection with soluble, nonaggregated αS resulted in paralysis and pathology in only a subset of mice, whereas soluble Δ71-82 αS, human βS, and keyhole limpet hemocyanin (KLH) control proteins induced no symptoms or pathology. Intraperitoneal injection of αS fibrils also induced CNS αS pathology in another αS transgenic mouse line (M20), albeit less robustly in these mice. In comparison, i.m. injection of αS fibrils was more efficient in inducing CNS αS pathology in M83 mice than i.p. or tail vein injections. Furthermore, i.m. injection of soluble, nonaggregated αS in M83+/− mice also induced paralysis and CNS αS pathology, although less efficiently. These results further demonstrate the prion-like characteristics of αS and reveal its efficiency to invade the CNS via multiple routes of peripheral administration. IMPORTANCE The misfolding and accumulation of α-synuclein (αS) inclusions are found in a number of neurodegenerative disorders and is a hallmark feature of Parkinson's disease (PD) and PD-related diseases. Similar characteristics have been observed between the infectious prion protein and αS, including its ability to spread from the peripheral nervous system and along neuroanatomical tracts within the central nervous system. In this study, we extend our previous results and investigate the efficiency of intravenous (i.v.), intraperitoneal (i.p.), and intramuscular (i.m.) routes of injection of αS fibrils and other protein controls. Our data reveal that injection of αS fibrils via these peripheral routes in αS-overexpressing mice are capable of inducing a robust αS pathology and in some cases cause paralysis. Furthermore, soluble, nonaggregated αS also induced αS pathology, albeit with much less efficiency. These findings further support and extend the idea of αS neuroinvasion from peripheral exposures.