Tau is a microtubule-associated protein implicated in neurodegenerative tauopathies. Alternative splicing of the tau gene (MAPT) generates six tau isoforms, distinguishable by the exclusion or inclusion of a repeat region of exon 10, which are referred to as 3-repeat (3R) and 4-repeat (4R) tau, respectively. We developed transgenic mouse models that express the entire human MAPT gene in the presence and absence of the mouse Mapt gene and compared the expression and regulation of mouse and human tau isoforms during development and in the young adult. We found differences between mouse and human tau in the regulation of exon 10 inclusion. Despite these differences, the isoform splicing pattern seen in normal human brain is replicated in our mouse models. In addition, we found that all tau, both in the neonate and young adult, is phosphorylated. We also examined the normal anatomic distribution of mouse and human tau isoforms in mouse brain. We observed developmental and species-specific variations in the expression of 3R- and 4R-tau within the frontal cortex and hippocampus. In addition, there were differences in the cellular distribution of the isoforms. Mice transgenic for the human MAPT gene exhibited higher levels of neuronal cell body expression of tau compared to wildtype mice. This neuronal cell body expression of tau was limited to the 3R isoform, whereas expression of 4R-tau was more "synaptic like," with granular staining of neuropil rather than in neuronal cell bodies. These developmental and species-specific differences in the regulation and distribution of tau isoforms may be important to the understanding of normal and pathologic tau isoform expression.

Brain lesions composed of pathological tau help to drive neurodegeneration in Alzheimer's disease (AD) and related tauopathies. Here, we identified the mammalian suppressor of tauopathy 2 (MSUT2) gene as a modifier of susceptibility to tau toxicity in two mouse models of tauopathy. Transgenic PS19 mice overexpressing tau, a model of AD, and lacking the Msut2 gene exhibited decreased learning and memory deficits, reduced neurodegeneration, and reduced accumulation of pathological tau compared to PS19 tau transgenic mice expressing Msut2 Conversely, Msut2 overexpression in 4RTauTg2652 tau transgenic mice increased pathological tau deposition and promoted the neuroinflammatory response to pathological tau. MSUT2 is a poly(A) RNA binding protein that antagonizes the canonical nuclear poly(A) binding protein PABPN1. In individuals with AD, MSUT2 abundance in postmortem brain tissue predicted an earlier age of disease onset. Postmortem AD brain tissue samples with normal amounts of MSUT2 showed elevated neuroinflammation associated with tau pathology. We observed co-depletion of MSUT2 and PABPN1 in postmortem brain samples from a subset of AD cases with higher tau burden and increased neuronal loss. This suggested that MSUT2 and PABPN1 may act together in a macromolecular complex bound to poly(A) RNA. Although MSUT2 and PABPN1 had opposing effects on both tau aggregation and poly(A) RNA tail length, we found that increased poly(A) tail length did not ameliorate tauopathy, implicating other functions of the MSUT2/PABPN1 complex in tau proteostasis. Our findings implicate poly(A) RNA binding proteins both as modulators of pathological tau toxicity in AD and as potential molecular targets for interventions to slow neurodegeneration in tauopathies.

Accumulation of insoluble conformationally altered hyperphosphorylated tau occurs as part of the pathogenic process in Alzheimer's disease (AD) and other tauopathies. In most AD subjects, wild-type (WT) tau aggregates and accumulates in neurofibrillary tangles and dystrophic neurites in the brain; however, in some familial tauopathy disorders, mutations in the gene encoding tau cause disease.

While BMPR2 mutation strongly predisposes to pulmonary arterial hypertension (PAH), only 20% of mutation carriers develop clinical disease. This finding suggests that modifier genes contribute to FPAH clinical expression. Since modifiers are likely to be common alleles, this problem is not tractable by traditional genetic approaches. Furthermore, examination of gene expression is complicated by confounding effects attributable to drugs and the disease process itself.

Pulmonary arterial hypertension (PAH) is a disease of progressively increasing pulmonary vascular resistance, associated with mutations of the type 2 receptor for the BMP pathway, BMPR2. The canonical signaling pathway for BMPR2 is through the SMAD family of transcription factors. BMPR2 is expressed in every cell type, but the impact of BMPR2 mutations affecting SMAD signaling, such as Bmpr2delx4+, had only previously been investigated in smooth muscle and endothelium. In the present study, we created a mouse with universal doxycycline-inducible expression of Bmpr2delx4+ in order to determine if broader expression had an impact relevant to the development of PAH. We found that the most obvious phenotype was a dramatic, but patchy, increase in pulmonary inflammation. We crossed these double transgenic mice onto an NF-κB reporter strain, and by luciferase assays on live mice, individual organs and isolated macrophages, we narrowed down the origin of the inflammatory phenotype to constitutive activation of tissue macrophages. Study of bone marrow-derived macrophages from mutant and wild-type mice suggested a baseline difference in differentiation state in Bmpr2 mutants. When activated with LPS, both mutant and wild-type macrophages secrete BMP pathway inhibitors sufficient to suppress BMP pathway activity in smooth muscle cells (SMC) treated with conditioned media. Functionally, co-culture with macrophages results in a BMP signaling-dependent increase in scratch closure in cultured SMC. We conclude that SMAD signaling through BMP is responsible, in part, for preventing macrophage activation in both live animals and in cells in culture, and that activated macrophages secrete BMP inhibitors in sufficient quantity to cause paracrine effect on vascular smooth muscle.

BACKGROUND: Hereditary pulmonary arterial hypertension(PAH) is usually caused by mutations in BMPR2. Mutations are found throughout the gene, and common molecular consequences of different types of mutation are not known. Knowledge of common molecular consequences would provide insight into molecular etiology of disease. The objective of this study was to determine common molecular consequences across classes of BMPR2 mutation. METHODS #ENTITYSTARTX00026; RESULTS: Increased superoxide and peroxide production, and alterations in genes associated with oxidative stress were a common consequence of stable transfection of vascular smooth muscle cells with three distinct classes of BMPR2 mutation, in the ligand binding domain, the kinase domain, and the cytoplasmic tail domain. Measurement of oxidized lipids in whole lung from transgenic mice expressing a mutation in the BMPR2 cytoplasmic tail showed a 50% increase in isoprostanes and a twofold increase in isofurans, suggesting increased ROS of mitochondrial origin. Immunohistochemistry on BMPR2 transgenic mouse lung showed that oxidative stress was vascular-specific. Electron microscopy showed decreased mitochondrial size and variability in pulmonary vessels from BMPR2 mutant mice. Measurement of oxidized lipids in urine from humans with BMPR2 mutations demonstrated increased ROS, regardless of disease status. Immunohistochemistry on HPAH patient lung confirmed oxidative stress specific to the vasculature. CONCLUSIONS: Increased oxidative stress, likely of mitochondrial origin, is a common consequence of BMPR2 mutation across mutation types in cell culture, mice, and humans.