Marcksl1 modulates endothelial cell mechanoresponse to haemodynamic forces to control blood vessel shape and size.

The formation of vascular tubes is driven by extensive changes in endothelial cell (EC) shape. Here, we have identified a role of the actin-binding protein, Marcksl1, in modulating the mechanical properties of EC cortex to regulate cell shape and vessel structure during angiogenesis. Increasing and depleting Marcksl1 expression level in vivo results in an increase and decrease, respectively, in EC size and the diameter of microvessels. Furthermore, endothelial overexpression of Marcksl1 induces ectopic blebbing on both apical and basal membranes, during and after lumen formation, that is suppressed by reduced blood flow. High resolution imaging reveals that Marcksl1 promotes the formation of linear actin bundles and decreases actin density at the EC cortex. Our findings demonstrate that a balanced network of linear and branched actin at the EC cortex is essential in conferring cortical integrity to resist the deforming forces of blood flow to regulate vessel structure.

Ectopic Expression Induces Abnormal Somatodendritic Distribution of Tau in the Mouse Brain.

Tau is a microtubule (MT)-associated protein that is localized to the axon. In Alzheimer's disease, the distribution of tau undergoes a remarkable alteration, leading to the formation of tau inclusions in the somatodendritic compartment. To investigate how this mislocalization occurs, we recently developed immunohistochemical tools that can separately detect endogenous mouse and exogenous human tau with high sensitivity, which allows us to visualize not only the pathological but also the pre-aggregated tau in mouse brain tissues of both sexes. Using these antibodies, we found that in tau-transgenic mouse brains, exogenous human tau was abundant in dendrites and somata even in the presymptomatic period, whereas the axonal localization of endogenous mouse tau was unaffected. In stark contrast, exogenous tau was properly localized to the axon in human tau knock-in mice. We tracked this difference to the temporal expression patterns of tau. Endogenous mouse tau and exogenous human tau in human tau knock-in mice exhibited high expression levels during the neonatal period and strong suppression into the adulthood. However, human tau in transgenic mice was expressed continuously and at high levels in adult animals. These results indicated the uncontrolled expression of exogenous tau beyond the developmental period as a cause of mislocalization in the transgenic mice. Superresolution microscopic and biochemical analyses also indicated that the interaction between MTs and exogenous tau was impaired only in the tau-transgenic mice, but not in knock-in mice. Thus, the ectopic expression of tau may be critical for its somatodendritic mislocalization, a key step of the tauopathy.SIGNIFICANCE STATEMENT Somatodendritic localization of tau may be an early step leading to the neuronal degeneration in tauopathies. However, the mechanisms of the normal axonal distribution of tau and the mislocalization of pathological tau remain obscure. Our immunohistochemical and biochemical analyses demonstrated that the endogenous mouse tau is transiently expressed in neonatal brains, that exogenous human tau expressed corresponding to such tau expression profile can distribute into the axon, and that the constitutive expression of tau into adulthood (e.g., human tau in transgenic mice) results in abnormal somatodendritic localization. Thus, the expression profile of tau is tightly associated with the localization of tau, and the ectopic expression of tau in matured neurons may be involved in the pathogenesis of tauopathy.

Distribution of endogenous normal tau in the mouse brain.

Tau is a microtubule-associated protein (MAP) that is localized to the axon. In Alzheimer's disease (AD), the distribution of tau undergoes a remarkable alteration, leading to the formation of tau inclusions in the somatodendritic compartment. While the abnormal aggregated tau has been extensively studied in human patient tissues and animal models of AD, how normal tau localizes to the axon, which would be the foundation to understand how the mis-localization occurs, has not been well studied due to the poor detectability of normal unaggregated tau in vivo. Therefore, we developed immunohistochemical techniques that can detect normal mouse and human tau in brain tissues with high sensitivity. Using these techniques, we demonstrate the global distribution of tau in the mouse brain and confirmed that normal tau is exclusively localized to the axonal compartment in vivo. Interestingly, tau antibodies strongly labeled nonmyelinated axons such as hippocampal mossy fibers, while white matters generally exhibited low levels of immunoreactivity. Furthermore, mouse tau is highly expressed not only in neurons but also in oligodendrocytes. With super resolution imaging using the stimulated-depletion microscopy, axonal tau appeared punctate rather than fibrous, indicating that tau decorates microtubules sparsely. Co-labeling with presynaptic and postsynaptic markers revealed that normal tau is not localized to synapses but sparsely distributes in the axon. Taken together, this study reports novel antibodies to investigate the localization and mis-localization of tau in vivo and novel findings of normal tau localization in the mouse brain.

Secreted Frizzled-related protein 1 (Sfrp1) regulates the progression of renal fibrosis in a mouse model of obstructive nephropathy.

Renal fibrosis is responsible for progressive renal diseases that cause chronic renal failure. Sfrp1 (secreted Frizzled-related protein 1) is highly expressed in kidney, although little is known about connection between the protein and renal diseases. Here, we focused on Sfrp1 to investigate its roles in renal fibrosis using a mouse model of unilateral ureteral obstruction (UUO). In wild-type mice, the expression of Sfrp1 protein was markedly increased after UUO. The kidneys from Sfrp1 knock-out mice showed significant increase in expression of myofibrobast markers, α-smooth muscle actin (αSMA). Sfrp1 deficiency also increased protein levels of the fibroblast genes, vimentin, and decreased those of the epithelial genes, E-cadherin, indicated that enhanced epithelial-to-mesenchymal transition. There was no difference in the levels of canonical Wnt signaling; rather, the levels of phosphorylated c-Jun and JNK were more increased in the Sfrp1(-/-) obstructed kidney. Moreover, the apoptotic cell population was significantly elevated in the obstructed kidneys from Sfrp1(-/-) mice following UUO but was slightly increased in those from wild-type mice. These results indicate that Sfrp1 is required for inhibition of renal damage through the non-canonical Wnt/PCP pathway.

Adequate Time Window and Environmental Factors Supporting Retinal Graft Cell Survival in rd Mice.

Postnatal photoreceptor cells can be integrated into the wild-type adult retina in mice, and retinal transplantation is now one therapeutic option for retinal degenerative diseases when photoreceptor degeneration is the primary cause of the disease. The aim of this study was to specify the optimal time window during the course of retinal degeneration and to modulate the host and/or graft environment for a successful transplantation. We first studied the background features of the mice with phosphodiesterase 6b (PDE6b) gene mutation (rd; C3H/Hej) and found that the infiltration of microglia and glial fibrillary acidic protein (GFAP) expression once increased at the peak of rod death (∼2-3 weeks of age) but then reduced for a following period until gliosis began to take place with enhanced GFAP expression (∼8 weeks of age). The postnatal retinal cells (p4-p7) were successfully transplanted during this period with neurite extension into the host retina. In later transplantations (6 or 8 weeks of age), graft cells survived better in the presence of chondroitinase ABC (ChABC), which digests chondroitin sulfate proteoglycan (CSPG), an essential component of gliosis. In contrast, in earlier transplantations (4 weeks of age), graft cells survived better in the presence of valproic acid (VPA), a neural differentiating reagent, or glatiramer acetate, an immune modulator. These suggest that, immediately after the outer nuclear layer (ONL) degeneration, an inflammatory reaction may be easily induced but the host neurons may be more able to accept donor cells in the presence of neural differentiating factor. These results will help optimize transplantation conditions when we consider clinical application.