Matrix metalloproteinase-9 and stromal cell-derived factor-1 act synergistically to support migration of blood-borne monocytes into the injured spinal cord.

The infiltration of monocytes into the lesioned site is a key event in the inflammatory response after spinal cord injury (SCI). We hypothesized that the molecular events governing the infiltration of monocytes into the injured cord involve cooperativity between the upregulation of the chemoattractant stromal cell-derived factor-1 (SDF-1)/CXCL12 in the injured cord and matrix metalloproteinase-9 (MMP-9/gelatinase B), expressed by infiltrating monocytes. SDF-1 and its receptor CXCR4 mRNAs were upregulated in the injured cord, while macrophages immunoexpressed CXCR4. When mice, transplanted with bone marrow cells from green fluorescent protein (GFP) transgenic mice, were subjected to SCI, GFP+ monocytes infiltrated the cord and displayed gelatinolytic activity. In vitro studies confirmed that SDF-1α, acting through CXCR4, expressed on bone marrow-derived macrophages, upregulated MMP-9 and stimulated MMP-9-dependent transmigration across endothelial cell monolayers by 2.6-fold. There was a reduction in F4/80+ macrophages in spinal cord-injured MMP-9 knock-out mice (by 36%) or wild-type mice, treated with the broad-spectrum MMP inhibitor GM6001 (by 30%). Mice were adoptively transferred with myeloid cells and treated with the MMP-9/-2 inhibitor SB-3CT, the CXCR4 antagonist AMD3100, or a combination of both drugs. While either drug resulted in a 28-30% reduction of infiltrated myeloid cells, the combined treatment resulted in a 45% reduction, suggesting that SDF-1 and MMP-9 function independently to promote the trafficking of myeloid cells into the injured cord. Collectively, these observations suggest a synergistic partnership between MMP-9 and SDF-1 in facilitating transmigration of monocytes into the injured spinal cord.

Human peripheral blood-derived CD31+ cells have robust angiogenic and vasculogenic properties and are effective for treating ischemic vascular disease.

OBJECTIVES: This study aimed to determine if CD31 is a novel marker of a circulating angio-vasculogenic cell population and to establish the cells' therapeutic effects on experimental ischemia. BACKGROUND: Emerging evidence suggested that therapeutic mechanisms underlying various bone marrow-derived cells are due to paracrine effects. Furthermore, the vasculogenic potential of these cells is under debate. CD31 is a well-known marker for endothelial cells but is also expressed in a fraction of peripheral blood (PB) mononuclear cells. METHODS: CD31(+) cells were isolated from human PB by magnetic-activated cell sorting. The gene expression profile was examined by deoxyribonucleic acid microarray and real-time reverse transcriptase polymerase chain reaction. Various in vitro endothelial differentiation or vasculogenic assays were conducted. Finally, cells were directly implanted into a mouse hind limb ischemia model to test angiogenic-vasculogenic and therapeutic effects. RESULTS: Fluorescent-activated cell sorter analysis revealed that PB-CD31(+) cells exhibited endothelial and hematopoietic stem/progenitor markers. CD31(+) cells had higher levels of expression of proangiogenic genes on microarray and real-time reverse transcriptase polymerase chain reaction and generated higher numbers of endothelial progenitor cells than CD31(-) cells did. CD31(+) cells spontaneously formed vascular tubelike structures and exhibited an endothelial cell phenotype in vitro. In a hind limb ischemia model, CD31(+) cell transplantation augmented blood perfusion and prevented limb loss. Both angiogenic cytokines and capillary density were increased, suggesting CD31(+) cells augmented neovascularization. CONCLUSIONS: CD31 is a novel marker that designates circulating angiogenic and vasculogenic cells. These cells are easily isolated from human PB and thus are a novel candidate for treatment of ischemic cardiovascular disease.

Dual angiogenic and neurotrophic effects of bone marrow-derived endothelial progenitor cells on diabetic neuropathy.

BACKGROUND: Endothelial progenitor cells (EPCs) are known to promote neovascularization in ischemic diseases. Recent evidence suggested that diabetic neuropathy is causally related to impaired angiogenesis and deficient growth factors. Accordingly, we investigated whether diabetic neuropathy could be reversed by local transplantation of EPCs. METHODS AND RESULTS: We found that motor and sensory nerve conduction velocities, blood flow, and capillary density were reduced in sciatic nerves of streptozotocin-induced diabetic mice but recovered to normal levels after hind-limb injection of bone marrow-derived EPCs. Injected EPCs were preferentially and durably engrafted in the sciatic nerves. A portion of engrafted EPCs were uniquely localized in close proximity to vasa nervorum, and a smaller portion of these EPCs were colocalized with endothelial cells. Multiple angiogenic and neurotrophic factors were significantly increased in the EPC-injected nerves. These dual angiogenic and neurotrophic effects of EPCs were confirmed by higher proliferation of Schwann cells and endothelial cells cultured in EPC-conditioned media. CONCLUSIONS: We demonstrate for the first time that bone marrow-derived EPCs could reverse various manifestations of diabetic neuropathy. These therapeutic effects were mediated by direct augmentation of neovascularization in peripheral nerves through long-term and preferential engraftment of EPCs in nerves and particularly vasa nervorum and their paracrine effects. These findings suggest that EPC transplantation could represent an innovative therapeutic option for treating diabetic neuropathy.

Matrix metalloproteinase-2 facilitates wound healing events that promote functional recovery after spinal cord injury.

Matrix metalloproteinases (MMPs) are proteolytic enzymes that are involved in both injury and repair mechanisms in the CNS. Pharmacological blockade of MMPs, limited to the first several days after spinal cord injury, improves locomotor recovery. This beneficial response is, however, lost when treatment is extended beyond the acutely injured cord to include wound healing and tissue remodeling. This suggests that some MMPs play a beneficial role in wound healing. To test this hypothesis, we investigated the role of MMP-2, which is actively expressed during wound healing, in white matter sparing and axonal plasticity, the formation of a glial scar, and locomotor recovery after spinal cord injury. MMP-2 increased between 7 and 14 d after injury, where it was immunolocalized in reactive astrocytes bordering the lesion epicenter. There was reduced white matter sparing and fewer serotonergic fibers, caudal to the lesion in injured MMP-2 null animals. MMP-2 deficiency also resulted in increased immunoreactivity to chondroitin sulfate proteoglycans and a more extensive astrocytic scar. Most importantly, locomotion in an open field, performance on a rotarod, and grid walking were significantly impaired in injured MMP-2 null mice. Our findings suggest that MMP-2 promotes functional recovery after injury by regulating the formation of a glial scar and white matter sparing and/or axonal plasticity. Thus, strategies exploiting MMPs as therapeutic targets must balance these beneficial effects during wound healing with their adverse interactions in the acutely injured spinal cord.

Activation of cyclin-dependent kinase 5 is involved in axonal regeneration.

Cyclin-dependent kinase 5 (Cdk5) is a serine-threonine kinase that is activated by the binding of p35 or p39 regulatory protein. Cdk5 and p35 are highly localized in the growth cone of cultured neurons, and Cdk5 activity is associated with neurite outgrowth. Here we report evidence on the functional involvement of Cdk5 kinase in regenerating peripheral nerve fibers. Elevated levels of Cdk5 protein were found in regenerating axons of facial motor neurons after nerve crush, and Cdk5 kinase activity was increased with a similar time course as increases in Cdk5 protein levels. The p35 protein was also found to be associated with increased Cdk5 activity in regenerating nerves. Administration of Cdk5 inhibitors, roscovitine and olomoucine, into the crushed nerves resulted in decreases in Cdk5 kinase activity in nerves and retardation of nerve fiber regrowth. Retardation of axonal regeneration by Cdk5 inhibition was confirmed by reduced labeling of facial motor neurons using retrograde tracer fluorogold (FG). These findings provide first in vivo evidence indicating that Cdk5 activity, which is induced by axonal injury, may play an important role in axonal regeneration.