Rett syndrome is an X-linked autism spectrum disorder. The disease is characterized in the majority of cases by mutation of the MECP2 gene, which encodes a methyl-CpG-binding protein 1–5. Although MeCP2 is expressed in many tissues, the disease is generally attributed to a primary neuronal dysfunction 6. However, as shown recently, glia, specifically astrocytes, also contribute to Rett pathophysiology. Here we examined the role of another form of glia, microglia, in a murine model of Rett syndrome. Transplantation of wild type bone marrow into irradiation-conditioned Mecp2-null hosts resulted in engraftment of brain parenchyma by bone marrow-derived myeloid cells of microglial phenotype, and arrest of disease development. However, when cranial irradiation was blocked by lead shield, and microglial engraftment was prevented, disease was not arrested. Similarly, targeted expression of Mecp2 in myeloid cells, driven by Lysmcre on an Mecp2-null background, dramatically attenuated disease symptoms. Thus, via multiple approaches, wild type Mecp2-expressing microglia within the context of an Mecp2-null male mouse arrested numerous facets of disease pathology; lifespan was increased; breathing patterns were normalized; apneas were reduced; body weight was increased to near wild type, and locomotor activity was improved. Mecp2+/− females also exhibited significant improvements as a result of wild type microglial engraftment. These benefits mediated by wild type microglia, however, were diminished when phagocytic activity was inhibited pharmacologically using annexin V to block phosphatydilserine residues on apoptotic targets, thus preventing recognition and engulfment by tissue-resident phagocytes. These results suggest the importance of microglial phagocytic activity in Rett syndrome. Our data implicate microglia as major players in Rett pathophysiology, and suggest that bone marrow transplantation might offer a feasible therapeutic approach for this devastating disorder.

Whereas thousands of new neurons are generated daily during adult life, only a fraction of them survive and become part of neural circuits; the rest die, and their corpses are presumably cleared by resident phagocytes. How the dying neurons are removed and how such clearance influences neurogenesis are not well understood. Here, we identify an unexpected phagocytic role for the doublecortin (DCX)-positive neuronal progenitor cells during adult neurogenesis. Our in vivo and ex vivo studies demonstrate that DCX+ cells comprise a significant phagocytic population within the neurogenic zones. Intracellular engulfment protein ELMO1, which promotes Rac activation downstream of phagocytic receptors, was required for phagocytosis by DCX+ cells. Disruption of engulfment in vivo genetically (in Elmo1-null mice) or pharmacologically (in wild-type mice) led to reduced uptake by DCX+ cells, accumulation of apoptotic nuclei in the neurogenic niches and impaired neurogenesis. Collectively, these findings indicate a paradigm wherein DCX+ neuronal precursors also serve as phagocytes, and that their phagocytic activity critically contributes to neurogenesis in the adult brain.

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The effect of phonon-electron (p-e) scattering on lattice thermal conductivity is investigated for Cu, Ag, Au, Al, Pt, and Ni. We evaluate both phonon-phonon (p-p) and p-e scattering rates from first principles and calculate the lattice thermal conductivity (j L). It is found that p-e scattering plays an important role in determining the j L of Pt and Ni at room temperature, while it has negligible effect on the j L of Cu, Ag, Au, and Al. Specifically, the room temperature j L s of Cu, Ag, Au, and Al predicted from density-functional theory calculations with the local density approximation are 16.9, 5.2, 2.6, and 5.8 W/m K, respectively, when only p-p scattering is considered, while it is almost unchanged when p-e scattering is also taken into account. However, the j L of Pt and Ni is reduced from 7.1 and 33.2 W/m K to 5.8 and 23.2 W/m K by p-e scattering. Even though Al has quite high electron-phonon coupling constant, a quantity that characterizes the rate of heat transfer from hot electrons to cold phonons in the two-temperature model, p-e scattering is not effective in reducing j L owing to the relatively low p-e scattering rates in Al. The difference in the strength of p-e scattering in different metals can be qualitatively understood by checking the amount of electron density of states that is overlapped with the Fermi window. Moreover, j L is found to be comparable to the electronic thermal conductivity in Ni. Published by AIP Publishing.

Thrombospondin 1 (TSP1), an oligomeric matrix protein, is known for its antiangiogenic activity. Recently, TSP1 has been shown to regulate synaptogenesis in the developing brain. In this study, we examine another role of TSP1 in the CNS, namely, in proliferation and differentiation of neural progenitor cells (NPCs). We found that adult mice deficient in TSP1 exhibit reduced proliferation of NPCs in vivo [13,330+/-826 vs. 4914+/-455 (mean+/-se wt vs. TSP1(-/-)); P<0.001, Student's t test] and impaired neuronal differentiation (1382+/-83 vs. 879+/-79; P<0.001). In vitro, NPC obtained from adult TSP1(-/-) mice display decreased proliferation in BrdU assay (48+/-8 vs. 24+/-3.5%; P<0.01) and decreased neuronal fate commitment (8+/-0.85 vs. 4.6+/-0.5%; P<0.05) in contrast to wild-type NPCs. Both proliferation and neuronal differentiation deficits are remediable in vitro by exogenous TSP1. Notably, conditioned medium from TSP1(-/-) astrocytes, unlike that from control astrocytes, fails to promote neurogenesis in wild-type NPCs, suggesting that TSP1 is one of the key molecules responsible for astrocyte-induced neurogenesis. Our data demonstrate that TSP1 is a critical participant in maintenance of the adult NPC pool and in neuronal differentiation.

Electron-phonon (e-p) interaction and transport are important for laser-matter interactions, hot-electron relaxation, and metal-nonmetal interfacial thermal transport. A widely used approach is the two-temperature model (TTM), where e-p coupling is treated with a gray approach with a lumped coupling factor G ep and the assumption that all phonons are in local thermal equilibrium. However, in many applications, different phonon branches can be driven into strong nonequilibrium due to selective e-p coupling, and a TTM analysis can lead to misleading or wrong results. Here, we extend the original TTM into a general multitemperature model (MTM), by using phonon branch-resolved e-p coupling factors and assigning a separate temperature for each phonon branch. The steady-state thermal transport and transient hot electron relaxation processes in constant and pulse laser-irradiated single-layer graphene (SLG) are investigated using our MTM respectively. Results show that different phonon branches are in strong nonequilibrium, with the largest temperature rise being more than six times larger than the smallest one. A comparison with TTM reveals that under steady state, MTM predicts 50% and 80% higher temperature rises for electrons and phonons respectively, due to the "hot phonon bottleneck" effect. Further analysis shows that MTM will increase the predicted thermal conductivity of SLG by 67% and its hot electron relaxation time by 60 times. We expect that our MTM will prove advantageous over TTM and gain use among experimentalists and engineers to predict or explain a wide ranges of processes involving laser-matter interactions.

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