CDK5 Targeting as a Therapy for Recovering Neurovascular Unit Integrity in Alzheimer’s Disease

The neurovascular unit (NVU) is responsible for synchronizing the energetic demand, vasodynamic changes, and neurochemical and electrical function of the brain through a closed and interdependent interaction of cell components conforming to brain tissue. In this review, we will focus on cyclin-dependent kinase 5 (CDK5) as a molecular pivot, which plays a crucial role in the healthy function of neurons, astrocytes, and the endothelium and is implicated in the cross-talk of cellular adhesion signaling, ion transmission, and cytoskeletal remodeling, thus allowing the individual and interconnected homeostasis of cerebral parenchyma. Then, we discuss how CDK5 overactivation affects the integrity of the NVU in Alzheimer’s disease (AD) and cognitive impairment; we emphasize how CDK5 is involved in the excitotoxicity spreading of glutamate and Ca2+ imbalance under acute and chronic injury. Additionally, we present pharmacological and gene therapy strategies for producing partial depletion of CDK5 activity on neurons, astrocytes, or endothelium to recover neuroplasticity and neurotransmission, suggesting that the NVU should be the targeted tissue unit in protective strategies. Finally, we conclude that CDK5 could be effective due to its intervention on astrocytes by its end feet on the endothelium and neurons, acting as an intermediary cell between systemic and central communication in the brain. This review provides integrated guidance regarding the pathogenesis of and potential repair strategies for AD.

The States of Pluripotency: Pluripotent Lineage Development in the Embryo and in the Dish

The pluripotent cell lineage of the embryo comprises a series of temporally and functionally distinct intermediary cell states, the epiblast precursor cell of the newly formed blastocyst, the epiblast population of the inner cell mass, and the early and late epiblast of the postimplantation embryo, referred to here as early and late primitive ectoderm. Pluripotent cell populations representative of the embryonic populations can be formed in culture. Although multiple pluripotent cell states are now recognised, little is known about the signals and pathways that progress cells from the epiblast precursor cell to the late primitive ectoderm in the embryo or in culture. The characterisation of cell states is most advanced in mouse where conditions for culturing distinct pluripotent cell states are well established and embryonic material is accessible. This review will focus on the pluripotent cell states present during embryonic development in the mouse and what is known of the mechanisms that regulate the progression of the lineage from the epiblast precursor cell and the ground state of pluripotency to the late primitive ectoderm present immediately prior to cell differentiation.

Ivig, but Not a Monoclonal Anti-RBC Antibody, Requires the Presence of Gr-1+ Cells to Ameliorate Immune Thrombocytopenia in a Murine Model

Abstract 268 Although there are many theories as to the mechanism of action of IVIg in the treatment of autoimmune disease, the exact pathway by which IVIg functions remains unclear. Many cell populations have been implicated in the IVIg pathway, including dendritic cells, which are considered to be one of the central initiators of IVIg effects, and macrophages, which are involved in platelet destruction. In addition, there is evidence from several groups that additional intermediary cell types may be involved. IVIg administration can induce a suppressive effect on peripheral blood neutrophil counts in ITP patients. In fact, alloimmunized thrombocytopenic patients, who display low neutrophil counts, do not respond to IVIg therapy. Here, we questioned whether Gr-1+cells (consisting primarily of neutrophils) are a critical cell type required for IVIg function, in a murine model of ITP. Another IVIg product which has ameliorative effects similar to IVIg but appears to function via a different mechanism is anti-D. We have previously shown that IVIg and a monoclonal antibody with “anti-D like” activity, TER-119, can successfully ameliorate thrombocytopenia in a murine model of ITP. In human patients as well as murine models of ITP, these 2 therapeutics appear to function via different mechanisms. Some work has shown that IVIg and anti-D work by the same, or overlapping mechanism, while other work shows a notable difference in that IVIg can cause neutropenia under conditions where it works to ameliorate autoimmune inflammation. Mice pretreated with 50 mg IVIg (∼2g/kg), or 50 ug TER-119 thirty min prior to administration of anti-platelet antibody MWReg30, show protection from thrombocytopenia compared with untreated mice. To assess the potential role for Gr-1+ cells in IVIg vs TER-119 mediated amelioration of murine ITP, we used RB6-8C5, a well described rat antibody for Gr-1+ cell depletion. Mice were injected with RB6-8C5 or control rat IgG 24 hr prior to thrombocytopenia induction. Mice pretreated with RB6-8C5 failed to respond to IVIg therapy compared with control mice. In contrast, Gr-1+ cell depletion had no effect on the ability of TER-119 to ameliorate the thrombocytopenia. This suggests that Gr-1+ cells likely play an essential role in IVIg function. In contrast, TER-119, does not depend on the presence of Gr-1+cells, suggesting that the mechanisms of action for IVIg and RBC specific antibodies are different for this requirement. In line with these observations, it has been observed that IVIg can modulate neutrophil activity, suggesting that in the murine ITP model, IVIg may function through a neutrophil dependent pathway. Experiments using more specific granulocyte antibodies will help ascertain whether neutrophils or some other Gr-1+ cell population is involved in IVIg function. Disclosures: No relevant conflicts of interest to declare.

IL-4 enhances IFN-λ1 (IL-29) production by plasmacytoid DCs via monocyte secretion of IL-1Ra

The type-III interferon (IFN) family is composed of 3 molecules in humans: IFN-λ1 (interleukin-29 [IL-29]), IFN-λ2 (IL-28A), and IFN-λ3 (IL-28B), each of which signals through the same receptor complex. Plasmacytoid dendritic cells (pDCs) are major IFN-λ producers among peripheral lymphocytes. Recently, it has been shown that IFN-λ1 exerts a powerful inhibitory effect over the T-helper 2 (Th2) response by antagonizing the effect of IL-4 on CD4+ T cells and inhibiting the production of Th2-associated cytokines. Here, we asked whether Th2 cytokines exert reciprocal control over IFN-λ production. IL-4 treatment during stimulation of human peripheral lymphocytes significantly elevated IFN-λ1 transcription and secretion. However, pDCs were not directly responsive to IL-4. Using depletion and reconstitution experiments, we showed that IL-4–responsive monocytes are an intermediary cell, responding to IL-4 by elevating their secretion of IL-1 receptor antagonist (IL-Ra); this IL-1Ra acts on pDCs to elevate their IFN-λ1 output. Thus, our experiments revealed a novel mechanism for regulation of both IFN-λ1 production and pDC function, and suggests an expanded immunomodulatory role for Th2-associated cytokines.

Generation of Functional Lymphoid (Natural Killer) Cells From Human ESC-Derived Hemangioblasts.

Abstract 1502 Poster Board I-525 Studies with human and mouse embryonic stem cells (ESCs) have shown that a common precursor to both vascular (endothelial and smooth muscle cells) and hematopoietic cell lineages called the hemangioblast can be produced from ESC-derived embryoid bodies in culture. We have developed a simple strategy to efficiently and reproducibly generate hemangioblasts from multiple hESC lines under serum- and stromal-free conditions, which will be important for their productive use in regenerative medicine. Previous work has shown that hESC-derived hemangioblasts can effectively differentiate into erythroid and myeloid lineages, but their ability to produce lymphoid lineage cells, including those with immunotherapeutic potential, is relatively unknown. Natural killer (NK) cells, which are part of the innate immune system, provide rapid, non-specific responses against viral infection and are involved in tumor cell detection and elimination. Interplay between various activating and inhibitory signals control the three main functions of NK cells, which are cytokine release, natural cytotoxicity, and antibody-dependent cellular cytotoxicity. Using hemangioblasts generated from both H7 and HuES-3 hESC lines, we have been able to produce mature CD56low/−CD16+ NK cells and found that their production does not require the use of stromal feeder layers. The differentiation procedure involves an initial 4 day culture to generate embryoid bodies, followed by a 12-14 day culture in methylcellulose supplemented with a set of cytokines and growth factors for the production and expansion of a hemangioblastic population. An additional 14-17 days in liquid culture plus human serum and a cocktail of cytokines allows for the differentiation of NK cells as assessed by flow cytometry. A non-radioactive cytotoxicity assay similar to the 51Cr release assay shows that these hemangioblast-derived NK cells harbor natural cytotoxicity function as they are able to effectively induce apoptosis in target K562 erythroblastic leukemia cells after a standard 4 hr co-culture. Using hemangioblasts as an intermediary cell source may enhance the capability and/or efficiency of hESCs to differentiate in vitro and importantly, allow for the development of feeder-free systems for the production of cells with immunotherapeutic potential. Disclosures: Kimbrel: Stem Cell & Regenerative Medicine International: Employment. Lu: Stem Cell & Regenerative Medicine International: Employment. Lanza: Stem Cell & Regenerative Medicine International/Advanced Cell Technology: Employment.

Astrocytes Function in Matching Blood Flow to Metabolic Activity

The brain possesses an intrinsic regulatory mechanism to maintain an adequate supply of O2 and nutrition despite local increases in neuronal activity. Brain astrocytes function as an intermediary cell type by responding to glutamate released from activated neurons, and they couple cerebral blood flow by producing cytochrome P-450-derived epoxyeicosatrienoic acids that induce vasodilation and increase capillary density.

An Alternate Pathway for T Cell Development Supported by the Bone Marrow Microenvironment: Recapitulation of Thymic Maturation

In the principal pathway of α/β T cell maturation, T cell precursors from the bone marrow migrate to the thymus and proceed through several well-characterized developmental stages into mature CD4+ and CD8+ T cells. This study demonstrates an alternative pathway in which the bone marrow microenvironment also supports the differentiation of T cell precursors into CD4+ and CD8+ T cells. The marrow pathway recapitulates developmental stages of thymic maturation including a CD4+CD8+ intermediary cell and positive and negative selection, and is strongly inhibited by the presence of mature T cells. The contribution of the marrow pathway in vivo requires further study in mice with normal and deficient thymic or immune function.