Summary Mesenchymal stem cells (MSCs) reside in the perivascular niche of many organs, including kidney, lung, liver, and heart, although their roles in these tissues are poorly understood. Here, we demonstrate that Gli1 marks perivascular MSC-like cells that substantially contribute to organ fibrosis. In vitro, Gli1+ cells express typical MSC markers, exhibit trilineage differentiation capacity, and possess colony-forming capacity, despite constituting a small fraction of the platelet-derived growth factor-β (PDGFRβ)+ cell population. Genetic lineage tracing analysis demonstrate that tissue-resident, but not circulating, Gli1+ cells proliferate following kidney, lung, liver, or heart injury to generate myofibroblasts. Genetic ablation of these cells substantially ameliorates kidney and heart fibrosis, and preserves ejection fraction in a model of induced heart failure. These findings implicate perivascular Gli1+ MSC-like cells as a major cellular origin of organ fibrosis and demonstrate these cells may be a relevant therapeutic target to prevent solid organ dysfunction following injury.

Recently we have established that the kidney tubular epithelium is repaired by surviving epithelial cells. It is not known, however, whether a population of intratubular adult progenitor cells are responsible for this epithelial repair after acute kidney injury. In this study, we used an unbiased DNA analog-based approach that does not rely on candidate markers to track multiple rounds of cell division in vivo. In the proximal tubule, robust thymidine analog incorporation was observed postinjury. Cell division was stochastic and enriched among cells that were injured and dedifferentiated. There was no evidence for the presence of a population of specialized progenitors that repeatedly divide in response to injury. Instead, these results indicate that after injury, new epithelial cells arise from self-duplication of surviving cells, most of which are injured. Because the renal papilla contains DNA label-retaining cells and has been proposed as a stem cell niche, we examined the proliferative behavior of these putative progenitors after ischemiareperfusion injury. Although label-retaining cells in the renal papilla diminished with time after ischemia-reperfusion injury, they neither proliferated nor migrated to the outer medulla or cortex. Thus, nonlethally injured cells repopulate the kidney epithelium after injury in the absence of any specialized progenitor cell population.

Activity-dependent changes in gene-expression are believed to underlie the molecular representation of memory. In this study, we report that in vivo activation of neurons rapidly induces the CREB-regulated microRNA miR-132. To determine if production of miR-132 is regulated by neuronal activity its expression in mouse brain was monitored by quantitative RT-PCR (RT-qPCR). Pilocarpine-induced seizures led to a robust, rapid, and transient increase in the primary transcript of miR-132 (pri-miR-132) followed by a subsequent rise in mature microRNA (miR-132). Activation of neurons in the hippocampus, olfactory bulb, and striatum by contextual fear conditioning, odor-exposure, and cocaine-injection, respectively, also increased pri-miR-132. Induction kinetics of pri-miR-132 were monitored and found to parallel those of immediate early genes, peaking at 45 minutes and returning to basal levels within two hours of stimulation. Expression levels of primary and mature-miR-132 increased significantly between postnatal days 10 and 24. We conclude that miR-132 is an activity-dependent microRNA in vivo, and may contribute to the long-lasting proteomic changes required for experience-dependent neuronal plasticity.