Injury to the CNS leads to formation of scar tissue, which is important in sealing the lesion and inhibiting axon regeneration. The fibrotic scar that comprises a dense extracellular matrix is thought to originate from meningeal cells surrounding the CNS. However, using transgenic mice, we demonstrate that perivascular collagen1␣1 cells are the main source of the cellular composition of the fibrotic scar after contusive spinal cord injury in which the dura remains intact. Using genetic lineage tracing, light sheet fluorescent microscopy, and antigenic profiling, we identify collagen1␣1 cells as perivascular fibroblasts that are distinct from pericytes. Our results identify collagen1␣1 cells as a novel source of the fibrotic scar after spinal cord injury and shift the focus from the meninges to the vasculature during scar formation.

Perforin-2 (MPEG1) is a pore-forming, antibacterial protein with broad-spectrum activity. Perforin-2 is expressed constitutively in phagocytes and inducibly in parenchymal, tissue-forming cells. In vitro, Perforin-2 prevents the intracellular replication and proliferation of bacterial pathogens in these cells. Perforin-2 knockout mice are unable to control the systemic dissemination of methicillin-resistant Staphylococcus aureus (MRSA) or Salmonella typhimurium and perish shortly after epicutaneous or orogastric infection respectively. In contrast, Perforin-2-sufficient littermates clear the infection. Perforin-2 is a transmembrane protein of cytosolic vesicles -derived from multiple organelles- that translocate to and fuse with bacterium containing vesicles. Subsequently, Perforin-2 polymerizes and forms large clusters of 100 Å pores in the bacterial surface with Perforin-2 cleavage products present in bacteria. Perforin-2 is also required for the bactericidal activity of reactive oxygen and nitrogen species and hydrolytic enzymes. Perforin-2 constitutes a novel and apparently essential bactericidal effector molecule of the innate immune system.DOI: http://dx.doi.org/10.7554/eLife.06508.001

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Perforin-2 (MPEG1) is an effector of the innate immune system that limits the proliferation and spread of medically relevant Gram-negative, -positive, and acid fast bacteria. We show here that a cullin-RING E3 ubiquitin ligase (CRL) complex containing cullin-1 and βTrCP monoubiquitylates Perforin-2 in response to pathogen associated molecular patterns such as LPS. Ubiquitylation triggers a rapid redistribution of Perforin-2 and is essential for its bactericidal activity. Enteric pathogens such as Yersinia pseudotuberculosis and enteropathogenic Escherichia coli disarm host cells by injecting cell cycle inhibiting factors (Cifs) into mammalian cells to deamidate the ubiquitin-like protein NEDD8. Because CRL activity is dependent upon NEDD8, Cif blocks ubiquitin dependent trafficking of Perforin-2 and thus, its bactericidal activity. Collectively, these studies further underscore the biological significance of Perforin-2 and elucidate critical molecular events that culminate in Perforin-2-dependent killing of both intracellular and extracellular, cell-adherent bacteria.DOI: http://dx.doi.org/10.7554/eLife.06505.001

Although infiltrating macrophages influence many pathological processes after spinal cord injury (SCI), the intrinsic molecular mechanisms that regulate their function are poorly understood. A major hurdle has been dissecting macrophage-specific functions from those in other cell types as well as understanding how their functions change over time. Therefore, we used the RiboTag method to obtain macrophage-specific mRNA directly from the injured spinal cord in mice and performed RNA sequencing to investigate their transcriptional profile. Our data show that at 7 d after SCI, macrophages are best described as foam cells, with lipid catabolism representing the main biological process, and canonical nuclear receptor pathways as their potential mediators. Genetic deletion of a lipoprotein receptor, CD36, reduces macrophage lipid content and improves lesion size and locomotor recovery. Therefore, we report the first macrophagespecific transcriptional profile after SCI and highlight the lipid catabolic pathway as an important macrophage function that can be therapeutically targeted after SCI.