Isolation and Structure of an Antibody that Fully Neutralizes Isolate SIVmac239 Reveals Functional Similarity of SIV and HIV Glycan Shields.

HIV- and SIV-envelope (Env) trimers are both extensively glycosylated, and antibodies identified to date have been unable to fully neutralize SIVmac239. Here, we report the isolation, structure, and glycan interactions of antibody ITS90.03, a monoclonal antibody that completely neutralized the highly neutralization-resistant isolate, SIVmac239. The co-crystal structure of a fully glycosylated SIVmac239-gp120 core in complex with rhesus CD4 and the antigen-binding fragment of ITS90.03 at 2.5-Å resolution revealed that ITS90 recognized an epitope comprised of 45% glycan. SIV-gp120 core, rhesus CD4, and their complex could each be aligned structurally to their human counterparts. The structure revealed that glycans masked most of the SIV Env protein surface, with ITS90 targeting a glycan hole, which is occupied in ∼83% of SIV strains by glycan N238. Overall, the SIV glycan shield appears to functionally resemble its HIV counterpart in coverage of spike, shielding from antibody, and modulation of receptor accessibility.

Surgical restabilization reduces the progression of post-traumatic osteoarthritis initiated by ACL rupture in mice.

OBJECTIVE: People who sustain joint injuries such as anterior cruciate ligament (ACL) rupture often develop post-traumatic osteoarthritis (PTOA). In human patients, ACL injuries are often treated with ACL reconstruction. However, it is still unclear how effective joint restabilization is for reducing the progression of PTOA. The goal of this study was to determine how surgical restabilization of a mouse knee joint following non-invasive ACL injury affects PTOA progression. DESIGN: In this study, 187 mice were subjected to non-invasive ACL injury or no injury. After injury, mice underwent restabilization surgery, sham surgery, or no surgery. Mice were then euthanized on day 14 or day 49 after injury/surgery. Functional analyses were performed at multiple time points to assess voluntary movement, gait, and pain. Knees were analyzed ex vivo with micro-computed tomography, RT-PCR, and whole-joint histology to assess articular cartilage degeneration, synovitis, and osteophyte formation. RESULTS: Both ACL injury and surgery resulted in loss of epiphyseal trabecular bone (-27-32%) and reduced voluntary movement at early time points. Joint restabilization successfully lowered OA score (-78% relative to injured at day 14, p < 0.0001), and synovitis scores (-37% relative to injured at day 14, p = 0.042), and diminished the formation of chondrophytes/osteophytes (-97% relative to injured at day 14, p < 0.001, -78% at day 49, p < 0.001). CONCLUSIONS: This study confirmed that surgical knee restabilization was effective at reducing articular cartilage degeneration and diminishing chondrophyte/osteophyte formation after ACL injury in mice, suggesting that these processes are largely driven by joint instability in this mouse model. However, restabilization was not able to mitigate the early inflammatory response and the loss of epiphyseal trabecular bone, indicating that these processes are independent of joint instability.

CD8ß Depletion Does Not Prevent Control of Viral Replication or Protection from Challenge in Macaques Chronically Infected with a Live Attenuated Simian Immunodeficiency Virus.

We evaluated the contribution of CD8αß+ T cells to control of live-attenuated simian immunodeficiency virus (LASIV) replication during chronic infection and subsequent protection from pathogenic SIV challenge. Unlike previous reports with a CD8α-specific depleting monoclonal antibody (mAb), the CD8ß-specific mAb CD8ß255R1 selectively depleted CD8αß+ T cells without also depleting non-CD8+ T cell populations that express CD8α, such as natural killer (NK) cells and γδ T cells. Following infusion with CD8ß255R1, plasma viremia transiently increased coincident with declining peripheral CD8αß+ T cells. Interestingly, plasma viremia returned to predepletion levels even when peripheral CD8αß+ T cells did not. Although depletion of CD8αß+ T cells in the lymph node (LN) was incomplete, frequencies of these cells were 3-fold lower (P = 0.006) in animals that received CD8ß255R1 than in those that received control IgG. It is possible that these residual SIV-specific CD8αß+ T cells may have contributed to suppression of viremia during chronic infection. We also determined whether infusion of CD8ß255R1 in the LASIV-vaccinated animals increased their susceptibility to infection following intravenous challenge with pathogenic SIVmac239. We found that 7/8 animals infused with CD8ß255R1, and 3/4 animals infused with the control IgG, were resistant to SIVmac239 infection. These results suggest that infusion with CD8ß255R1 did not eliminate the protection afforded to LASIV vaccination. This provides a comprehensive description of the impact of CD8ß255R1 infusion on the immunological composition in cynomolgus macaques, compared to an isotype-matched control IgG, while showing that the control of LASIV viremia and protection from challenge can occur even after CD8ß255R1 administration.IMPORTANCE Studies of SIV-infected macaques that deplete CD8+ T cells in vivo with monoclonal antibodies have provided compelling evidence for their direct antiviral role. These studies utilized CD8α-specific mAbs that target both the major (CD8αß+) and minor (CD8αα+) populations of CD8+ T cells but additionally deplete non-CD8+ T cell populations that express CD8α, such as NK cells and γδ T cells. In the current study, we administered the CD8ß-specific depleting mAb CD8ß255R1 to cynomolgus macaques chronically infected with a LASIV to selectively deplete CD8αß+ T cells without removing CD8αα+ lymphocytes. We evaluated the impact on control of virus replication and protection from pathogenic SIVmac239 challenge. These results underscore the utility of CD8ß255R1 for studying the direct contribution of CD8αß+ T cells in various disease states.

Select gp120 V2 domain specific antibodies derived from HIV and SIV infection and vaccination inhibit gp120 binding to α4ß7.

The GI tract is preferentially targeted during acute/early HIV-1 infection. Consequent damage to the gut plays a central role in HIV pathogenesis. The basis for preferential targeting of gut tissues is not well defined. Recombinant proteins and synthetic peptides derived from HIV and SIV gp120 bind directly to integrin α4ß7, a gut-homing receptor. Using both cell-surface expressed α4ß7 and a soluble α4ß7 heterodimer we demonstrate that its specific affinity for gp120 is similar to its affinity for MAdCAM (its natural ligand). The gp120 V2 domain preferentially engages extended forms of α4ß7 in a cation -sensitive manner and is inhibited by soluble MAdCAM. Thus, V2 mimics MAdCAM in the way that it binds to α4ß7, providing HIV a potential mechanism to discriminate between functionally distinct subsets of lymphocytes, including those with gut-homing potential. Furthermore, α4ß7 antagonists developed for the treatment of inflammatory bowel diseases, block V2 binding to α4ß7. A 15-amino acid V2 -derived peptide is sufficient to mediate binding to α4ß7. It includes the canonical LDV/I α4ß7 binding site, a cryptic epitope that lies 7-9 amino acids amino terminal to the LDV/I, and residues K169 and I181. These two residues were identified in a sieve analysis of the RV144 vaccine trial as sites of vaccine -mediated immune pressure. HIV and SIV V2 mAbs elicited by both vaccination and infection that recognize this peptide block V2-α4ß7 interactions. These mAbs recognize conformations absent from the ß- barrel presented in a stabilized HIV SOSIP gp120/41 trimer. The mimicry of MAdCAM-α4ß7 interactions by V2 may influence early events in HIV infection, particularly the rapid seeding of gut tissues, and supports the view that HIV replication in gut tissue is a central feature of HIV pathogenesis.

Genetic interaction between Lrp6 and Wnt5a during mouse development.

Lrp6 is generally described as a receptor required for signal transduction in the Wnt/beta-catenin pathway. Wnt5a, however, is a Wnt ligand that usually does not activate Wnt/beta-catenin but rather activates noncanonical Wnt signaling. We have previously shown that Lrp6 can inhibit noncanonical Wnt5a/Wnt11 signaling and that Lrp5/6 loss-of-function produces noncanonical gain-of function defects, which can be rescued by loss of Wnt5a. Here, we describe other phenotypes found in Wnt5a/Lrp6 compound mutant mice, including a worsening of individual Wnt5a or Lrp6 loss of function phenotypes. Lrp6 haploinsufficiency in a Wnt5a-/- background caused spina bifida and exacerbated posterior truncation. Wnt5a-/-Lrp6-/- embryos displayed presomitic mesoderm morphogenesis, somitogenesis, and neurogenesis defects, which are much more severe than in either of the single mutants. Interestingly these results reveal a further level of complexity in processes in which Wnt5a and LRP6 cooperate, or oppose each other, during mouse development.

Identification and comparative expression analyses of Daam genes in mouse and Xenopus.

During vertebrate embryogenesis, secreted Wnt molecules regulate cell fates by signaling through the canonical pathway mediated by beta-catenin, and regulate planar cell polarity (PCP) and convergent extension movements through alternative pathways. The phosphoprotein Dishevelled (Dsh/Dvl) is a Wnt signal transducer thought to function in all Wnt signaling pathways. A recently identified member of the Formin family, Daam (Dishevelled--associated activator of morphogenesis), regulates the morphogenetic movements of vertebrate gastrulation in a Wnt-dependent manner through direct interactions with Dsh/Dvl and RhoA. We describe two mouse Daam cDNAs, mDaam1 and mDaam2, which encode proteins characterized by highly conserved formin homology domains and which are expressed in complementary patterns during mouse development. Cross-species comparisons indicate that the expression domains of Xenopus Daam1 (XDaam1) mirror mDaam1 expression. Our results demonstrate that Daams are expressed in tissues known to require Wnts and are consistent with Daams being effectors of Wnt signaling during vertebrate development.

Two-color in situ hybridization of whole-mount mouse embryos.

RNA in situ hybridization is a powerful technique used to identify the spatial localization of a specific RNA in a tissue section or whole tissue. In this protocol, we describe a reliable method for two-color in situ hybridization that can be used to accurately assess the expression of multiple genes with contrasting or overlapping expression patterns in whole mouse embryos.

The Wnt3a/ß-catenin target gene Mesogenin1 controls the segmentation clock by activating a Notch signalling program.

Segmentation is an organizing principle of body plans. The segmentation clock, a molecular oscillator best illustrated by the cyclic expression of Notch signalling genes, controls the periodic cleavage of somites from unsegmented presomitic mesoderm during vertebrate segmentation. Wnt3a controls the spatiotemporal expression of cyclic Notch genes; however, the underlying mechanisms remain obscure. Here we show by transcriptional profiling of Wnt3a (-/-) embryos that the bHLH transcription factor, Mesogenin1 (Msgn1), is a direct target gene of Wnt3a. To identify Msgn1 targets, we conducted genome-wide studies of Msgn1 activity in embryonic stem cells. We show that Msgn1 is a major transcriptional activator of a Notch signalling program and synergizes with Notch to trigger clock gene expression. Msgn1 also indirectly regulates cyclic genes in the Fgf and Wnt pathways. Thus, Msgn1 is a central component of a transcriptional cascade that translates a spatial Wnt3a gradient into a temporal pattern of clock gene expression.

The extracellular domain of Lrp5/6 inhibits noncanonical Wnt signaling in vivo.

Lrp5/6 are crucial coreceptors for Wnt/beta-catenin signaling, a pathway biochemically distinct from noncanonical Wnt signaling pathways. Here, we examined the possible participation of Lrp5/6 in noncanonical Wnt signaling. We found that Lrp6 physically interacts with Wnt5a, but that this does not lead to phosphorylation of Lrp6 or activation of the Wnt/beta-catenin pathway. Overexpression of Lrp6 blocks activation of the Wnt5a downstream target Rac1, and this effect is dependent on intact Lrp6 extracellular domains. These results suggested that the extracellular domain of Lrp6 inhibits noncanonical Wnt signaling in vitro. In vivo, Lrp6-/- mice exhibited exencephaly and a heart phenotype. Surprisingly, these defects were rescued by deletion of Wnt5a, indicating that the phenotypes resulted from noncanonical Wnt gain-of-function. Similarly, Lrp5 and Lrp6 antisense morpholino-treated Xenopus embryos exhibited convergent extension and heart phenotypes that were rescued by knockdown of noncanonical XWnt5a and XWnt11. Thus, we provide evidence that the extracellular domains of Lrp5/6 behave as physiologically relevant inhibitors of noncanonical Wnt signaling during Xenopus and mouse development in vivo.

Wnt3a/beta-catenin signaling controls posterior body development by coordinating mesoderm formation and segmentation.

Somitogenesis is thought to be controlled by a segmentation clock, which consists of molecular oscillators in the Wnt3a, Fgf8 and Notch pathways. Using conditional alleles of Ctnnb1 (beta-catenin), we show that the canonical Wnt3a/beta-catenin pathway is necessary for molecular oscillations in all three signaling pathways but does not function as an integral component of the oscillator. Small, irregular somites persist in abnormally posterior locations in the absence of beta-catenin and cycling clock gene expression. Conversely, Notch pathway genes continue to oscillate in the presence of stabilized beta-catenin but boundary formation is delayed and anteriorized. Together, these results suggest that the Wnt3a/beta-catenin pathway is permissive but not instructive for oscillating clock genes and that it controls the anterior-posterior positioning of boundary formation in the presomitic mesoderm (PSM). The Wnt3a/beta-catenin pathway does so by regulating the activation of the segment boundary determination genes Mesp2 and Ripply2 in the PSM through the activation of the Notch ligand Dll1 and the mesodermal transcription factors T and Tbx6. Spatial restriction of Ripply2 to the anterior PSM is ensured by the Wnt3a/beta-catenin-mediated repression of Ripply2 in posterior PSM. Thus, Wnt3a regulates somitogenesis by activating a network of interacting target genes that promote mesodermal fates, activate the segmentation clock, and position boundary determination genes in the anterior PSM.

Mouse Ripply2 is downstream of Wnt3a and is dynamically expressed during somitogenesis.

Somites are blocks of mesoderm that form when segment boundaries are periodically generated in the anterior presomitic mesoderm (PSM). Periodicity is thought to be driven by an oscillating Notch-centered segmentation clock, whereas boundaries are spatially positioned by the secreted signaling molecules Wnt3a and Fgf8. We identified the putative transcriptional corepressor Ripply2 as a differentially expressed gene in wild-type and Wnt3a(-/-) embryos. Here, we show that Ripply2 is expressed in the anterior PSM and that it indeed lies downstream of Wnt3a. Dynamic Ripply2 expression in prospective somites S0 and S-I overlaps with the rostral expression of cycling genes in the Notch pathway, suggesting that Ripply2 may be controlled by the segmentation clock. Continued expression of Ripply2 in embryos lacking Hes7, a molecular oscillator in the Notch clock, indicates that Hes7 is not a major regulator of Ripply2. Our data are consistent with Ripply2 functioning as a segment boundary determination gene during mammalian embryogenesis. Developmental

Wnt3a links left-right determination with segmentation and anteroposterior axis elongation.

The alignment of the left-right (LR) body axis relative to the anteroposterior (AP) and dorsoventral (DV) axes is central to the organization of the vertebrate body plan and is controlled by the node/organizer. Somitogenesis plays a key role in embryo morphogenesis as a principal component of AP elongation. How morphogenesis is coupled to axis specification is not well understood. We demonstrate that Wnt3a is required for LR asymmetry. Wnt3a activates the Delta/Notch pathway to regulate perinodal expression of the left determinant Nodal, while simultaneously controlling the segmentation clock and the molecular oscillations of the Wnt/beta-catenin and Notch pathways. We provide evidence that Wnt3a, expressed in the primitive streak and dorsal posterior node, acts as a long-range signaling molecule, directly regulating target gene expression throughout the node and presomitic mesoderm. Wnt3a may also modulate the symmetry-breaking activity of mechanosensory cilia in the node. Thus, Wnt3a links the segmentation clock and AP axis elongation with key left-determining events, suggesting that Wnt3a is an integral component of the trunk organizer.