The myelin-associated glycoprotein inhibitor BENZ induces outgrowth and survival of rat dorsal root ganglion cell cultures

New Human CD22/Siglec-2 Ligands with a Triazole Glycoside

CD22 is a member of the Siglec family. Considerable attention has been drawn to the design and synthesis of new Siglec ligands to explore target biology and innovative therapies. In particular, CD22-ligand-targeted nanoparticles with therapeutic functions have proved successful in preclinical settings for blood cancers, autoimmune diseases, and tolerance induction. Here we report the design, synthesis and affinity evaluation of a new class of Siglec ligands: namely sialic acid derivatives with a triazole moiety replacing the natural glycoside oxygen atom. In addition, we describe important and surprising differences in binding to CD22 expressed at the cell surface for compounds with distinct valences. The new class of compounds might serve as a template for the design of ligands for other members of the Siglec family and next-generation CD22-ligand-based targeted therapies.

Impaired Axonal Regeneration in Diabetes. Perspective on the Underlying Mechanism from In Vivo and In Vitro Experimental Studies

Axonal regeneration after peripheral nerve injury is impaired in diabetes, but its precise mechanisms have not been elucidated. In this paper, we summarize the progress of research on altered axonal regeneration in animal models of diabetes and cultured nerve tissues exposed to hyperglycemia. Impaired nerve regeneration in animal diabetes can be attributed to dysfunction of neurons and Schwann cells, unfavorable stromal environment supportive of regenerating axons, and alterations of target tissues receptive to reinnervation. In particular, there are a number of factors such as enhanced activity of the negative regulators of axonal regeneration (e.g., phosphatase and tensin homolog deleted on chromosome 10 and Rho/Rho kinase), delayed Wallerian degeneration, alterations of the extracellular matrix components, enhanced binding of advanced glycation endproducts (AGEs) with the receptor for AGE, and delayed muscle reinnervation that can be obstacles to functional recovery after an axonal injury. It is also noteworthy that we and others have observed excessive neurite outgrowth from peripheral sensory ganglion explants from streptozotocin (STZ)-diabetic mice in culture and enhanced regeneration of small nerve fibers after sciatic nerve injury in STZ-induced diabetic rats. The excess of abortive neurite outgrowth may lead to misconnections of axons and target organs, which may interfere with appropriate target reinnervation and functional repair. Amelioration of perturbed nerve regeneration may be crucial for the future management of diabetic neuropathy.

Neurotrophic and neuroprotective properties of exendin-4 in adult rat dorsal root ganglion neurons: involvement of insulin and RhoA

Glucagon-like peptide-1 (GLP-1) is thought to preserve neurons and glia following axonal injury and neurodegenerative disorders. We investigated the neurotrophic and neuroprotective properties of exendin (Ex)-4, a synthetic GLP-1 receptor (GLP-1R) agonist, on adult rat dorsal root ganglion (DRG) neurons and PC12 cells. GLP-1R was predominantly localized on large and small peptidergic neurons in vivo and in vitro, suggesting the involvement of GLP-1 in both the large and small sensory fiber functions. Ex-4 dose-dependently (1 ≤ 10 ≤ 100 nM) promoted neurite outgrowth and neuronal survival at 2 and 7 days in culture, respectively. Treatment with 100 nM Ex-4 restored the reduced neurite outgrowth and viability of DRG neurons caused by the insulin removal from the medium and suppressed the activity of RhoA, an inhibitory regulator for peripheral nerve regeneration, in PC12 cells. Furthermore, these effects were attenuated by co-treatment with phosphatidylinositol-3'-phosphate kinase (PI3K) inhibitor, LY294002. These findings imply that Ex-4 enhances neurite outgrowth and neuronal survival through the activation of PI3K signaling pathway, which negatively regulates RhoA activity. Ex-4 and other GLP-1R agonists may compensate for the reduced insulin effects on neurons, thereby being beneficial for the treatment of diabetic neuropathy.

Discovery of multifold modified sialosides as human CD22/Siglec-2 ligands with nanomolar activity on B-cells

Sialic acids are abundant in higher domains of life and lectins recognizing sialosaccharides are heavily involved in the regulation of the human immune system. Modified sialosides are useful tools to explore the functions of those lectins, especially members of the Siglec (sialic acid binding immunoglobulin like lectin) family. Here we report design, synthesis, and affinity evaluation of novel sialoside classes with combined modification at positions 2, 4, and 9 or 2, 3, 4, and 9 of the sialic acid scaffold as human CD22 (human Siglec-2) ligands. They display up to 7.5 × 10(5)-fold increased affinity over αMe Neu5Ac (the minimal Siglec ligand). CD22 is a negative regulating coreceptor of the B-cell receptor (BCR). In vitro experiments with a human B-lymphocyte cell line showed functional blocking of CD22 upon B-cell receptor (BCR) stimulation in the presence of nanomolar concentrations of the novel ligands. The observed increased Ca(2+) response corresponds to enhanced cell activation, providing an opportunity to therapeutically modulate B-lymphocyte responses, e.g., in immune deficiencies and infections.

Apolipoproteins D and E3 exert neurotrophic and synaptogenic effects in dorsal root ganglion cell cultures

Co-cultures of 3T3-L1 adipocytes with neurons from the rat dorsal root ganglia (DRG) showed enhanced neuritogenesis and synaptogenesis. Microarray analysis for upregulated genes in adipocyte/DRG co-cultures currently points to apolipoproteins D and E (ApoD, ApoE) as influential proteins. We therefore tested adipocyte-secreted cholesterol and the carrier proteins ApoD and ApoE3. Cholesterol, ApoD, and ApoE3 each increased neurite outgrowth and upregulated the expression of presynaptic synaptophysin and synaptotagmin, as well as the postsynaptic density protein 95. The neurotrophic effects of ApoD and ApoE3 were associated with an increased expression of the low-density lipoprotein receptor and apolipoprotein E receptor 2. Simultaneous treatment with receptor-associated protein, an apolipoprotein receptor antagonist, inhibited the neurotrophic function of both apolipoproteins. The application of ApoD, ApoE3, and cholesterol to DRG cell cultures corresponded with increased expression of the chemokine stromal cell-derived factor 1 and its receptor CXC chemokine receptor 4 (CXCR4). Surprisingly, the inhibition of CXCR4 by the antagonistic drug AMD3100 decreased the apolipoprotein/cholesterol dependent neurotrophic effects. We thus assume that apolipoprotein-induced neuritogenesis in DRG cells interferes with CXCR4 signaling, and that adipocyte-derived apolipoproteins might be helpful in nerve repair.

UnPAKing the class differences among p21-activated kinases

The p21-activated kinases (PAKs) are signal transducers, central to many vital cellular processes, including cell morphology, motility, survival, gene transcription and hormone signalling. The mammalian PAK family contains six serine/threonine kinases divided into two subgroups, group I (PAK 1-3) and group II (PAK4-6), based on their domain architecture and regulation. PAKs functioning as dynamic signalling nodes present themselves as attractive therapeutic targets in tumours, neurological diseases and infection. The recent findings across all PAKs, including newly reported structures, shed light on the cellular functions of PAKs, highlighting molecular mechanisms of activation, catalysis and substrate specificity. We believe that a comprehensive understanding of the entire PAK family is essential for developing strategies towards PAK-targeted therapeutics.