Background— Stroke is a leading cause of death and disability worldwide; however, no effective treatment currently exists. Methods and Results— Rats receiving subcutaneous granulocyte colony-stimulating factor (G-CSF) showed less cerebral infarction, as evaluated by MRI, and improved motor performance after right middle cerebral artery ligation than vehicle-treated control rats. Subcutaneous administration of G-CSF enhanced the availability of circulating hematopoietic stem cells to the brain and their capacity for neurogenesis and angiogenesis in rats with cerebral ischemia. Conclusions— G-CSF induced increases in bone marrow cell mobilization and targeting to the brain, reducing the volume of cerebral infarction and improving neural plasticity and vascularization.

A number of human diseases are caused by inherited mitochondrial DNA mutations. Two of these diseases, MELAS (mitochondrial myopathy, encephalopathy, lactic acidosis and stroke-like episodes) and MERRF (myoclonic epilepsy and ragged-red fibres), are commonly caused by point mutations to tRNA genes encoded by mitochondrial DNA. Here we report on how these mutations affect mitochondrial function in primary fibroblast cultures established from a MELAS patient containing an A to G mutation at nucleotide 3243 in the tRNA^Leu(UUR) gene and a MERRF patient containing an A to G mutation at nucleotide 8344 in the tRNA^Lys gene. Both mitochondrial membrane potential and respiration rate were significantly decreased in digitonin-permeabilized MELAS and MERRF fibroblasts respiring on glutamate/malate. A similar decrease in mitochondrial membrane potential was found in intact MELAS and MERRF fibroblasts. The mitochondrial content of these cells, estimated by stereological analysis of electron micrographs and from measurement of mitochondrial marker enzymes, was similar in control, MELAS and MERRF cells. Therefore, in cultured fibroblasts, mutation of mitochondrial tRNA genes leads to assembly of bioenergetically incompetent mitochondria, not to an alteration in their amount. However, the cell volume occupied by secondary lysosomes and residual bodies in the MELAS and MERRF cells was greater than in control cells, suggesting increased mitochondrial degradation in these cells. In addition, fibroblasts containing mitochondrial DNA mutations were 3–4-fold larger than control fibroblasts. The implications of these findings for the pathology of mitochondrial diseases are discussed.

Mutations and deletions in mitochondrial DNA (mtDNA) lead to a number of human diseases characterized by neuromuscular degeneration. Accumulation of truncated mtDNA molecules (Δ‐mtDNA) lacking a specific 4977‐bp fragment, the common deletion, leads to three related mtDNA diseases : Pearson's syndrome; Kearns‐Sayre syndrome; and chronic progressive external ophthalmoplegia (CPEO). In addition, the proportion of Δ‐mtDNA present increases with age in a range of tissues. Consequently, there is considerable interest in the effects of the accumulation of Δ‐mtDNA on cell function. The 4977‐bp deletion affects genes encoding 7 polypeptide components of the mitochondrial respiratory chain, and 5 of the 22 tRNAs necessary for mitochondrial protein synthesis. To determine how the accumulation of Δ‐mtDNA affects oxidative phosphorylation we constructed a series of cybrids by fusing a human osteosarcoma cell line depleted of mtDNA (@gR⁰) with enucleated skin fibroblasts from a CPEO patient. The ensuing cybrids contained 0−86 %Δ‐mtDNA and all had volumes, protein contents, plasma‐membrane potentials and mitochondrial contents similar to those of the parental cell line. The bioenergetic consequences of accumulating Δ‐mtDNA were assessed by measuring the mitochondrial membrane potential, rate of ATP synthesis and ATP/ADP ratio. In cybrids containing less than 50−55 %Δ‐mtDNA, these bioenergetic functions were equivalent to those of cybrids with intact mtDNA. However, once the proportion of Δ‐mtDNA exceeded this threshold, the mitochondrial membrane potential, rate of ATP synthesis, and cellular ATP/ADP ratio decreased. These bioenergetic deficits will contribute to the cellular pathology associated with the accumulation of Δ‐mtDNA in the target tissues of patients with mtDNA diseases.