PHD2 serves as an oxygen sensor that rescues blood supply by regulating vessel formation and shape in case of oxygen shortage1–5. However, it is unknown whether PHD2 can influence arteriogenesis. Here we studied the role of PHD2 in collateral artery growth by using hindlimb ischaemia as a model, a process that compensates for the lack of blood flow in case of major arterial occlusion6–8. We show that Phd2 (also known as Egln1) haplodeficient (Phd2+/−) mice displayed preformed collateral arteries that preserved limb perfusion and prevented tissue necrosis in ischaemia. Improved arteriogenesis in Phd2+/− mice was due to an expansion of tissue-resident, M2-like macrophages9,10 and their increased release of arteriogenic factors, leading to enhanced smooth muscle cell (SMC) recruitment and growth. Both chronic and acute deletion of one Phd2 allele in macrophages was sufficient to skew their polarization towards a proarteriogenic phenotype. Mechanistically, collateral vessel preconditioning relied on the activation of canonical NF-κB pathway in Phd2+/− macrophages. These results unravel how PHD2 regulates arteriogenesis and artery homeostasis by controlling a specific differentiation state in macrophages and suggest new treatment options for ischaemic disorders.

Murine bone marrow stromal cells differentiate not only into mesodermal derivatives, such as osteocytes, chondrocytes, adipocytes, skeletal myocytes, and cardiomyocytes, but also into neuroectodermal cells in vitro.Human bone marrow stromal cells are easy to isolate but difficult to study because of their limited life span. To overcome this problem, we attempted to prolong the life span of bone marrow stromal cells and investigated whether bone marrow stromal cells modified with bmi-1, hTERT, E6, and E7 retained their differentiated capability, or multipotency. In this study, we demonstrated that the life span of bone marrow stromal cells derived from a 91-year-old donor could be extended and that the stromal cells with an extended life span differentiated into neuronal cells in vitro. We examined the neuronally differentiated cells morphologically, physiologically, and biologically and compared the gene profiles of undifferentiated and differentiated cells. The neuronally differentiated cells exhibited characteristics similar to those of midbrain neuronal progenitors. Thus, the results of this study support the possible use of autologous-cell graft systems to treat central nervous system diseases in geriatric patients.Murine and human bone marrow stromal cells differentiate into osteoblasts (2), chondrocytes (13), skeletal myocytes, adipocytes, and cardiomyocytes (24) in vitro and thus are a useful cell source for bone regeneration (26) and in vivo cardiovasculogenesis (11). However, recent studies suggest that bone marrow stromal cells can also differentiate into a neuronal lineage (22), and murine bone marrow-derived multipotent adult progenitor cells differentiate into dopaminergic neuronal cells (16). Since the use of bone marrow stromal cells entails no ethical or immunological problems, and bone marrow aspiration is an established routine procedure, they may be a useful source of cells for transplantation.Large numbers of cells may be necessary for repairing damaged human tissues to restore function. However, there have been no reports of a sufficient number of differentiated neurons ever having been obtained from human marrow stromal cells. One reason is that normal human cells undergo a limited number of divisions in culture and then enter a nondividing state referred to as "senescence." Senescence is classified into two categories: "stress-induced premature senescence," or "telomere-independent senescence," and "replicative senescence," or "telomere-dependent senescence" (3, 5, 38). p16 Ink4a (p16), a cyclin-dependent kinase (CDK) inhibitor, is induced by certain oncogenes and other damage or stress signals and is required for "premature senescence" in human mammary epithelial cells and keratinocytes. p16 inhibits dephosphorylation of pRb by Cdk4/6-cyclin D, and hypophosphorylated pRb actively represses the genes required for the S phase by sequestering the E2F transcription factors. "Replicative senescence" is caused by telomere size reduction during successive cell divisions because of the chromosome...

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