Postdoctoral Scholar, University of California San Diego
Chemically synthesized glycomaterials that recapitulate the functions of native glycans
Glycans are important constituents that decorate the eukaryotic cell surface. Due to their chemical complexity, however, glycans are less studied compared to their protein counterparts. Here, we present a chemical strategy to mimic the natural macromolecular architecture of a class of glycans, termed glycosaminoglycans, in order to study their role in the developing neuromuscular junction. Our strategy presents an elegant solution towards the synthesis of chemically-defined homogeneous glycosaminoglycan conjugates, while obviating laborious synthetic procedures. Using these materials, we successfully recapitulated the functions of native muscle glycosaminoglycans. Furthermore, we discovered a differing role for soluble versus cell-surface anchored glycosaminoglycans in regulating the neuromuscular synapse.
Abstract: Spinal muscular atrophy (SMA) is a common and often fatal neuromuscular disorder caused by low levels of the Survival Motor Neuron (SMN) protein. Amongst the earliest detectable consequences of SMN deficiency are profound defects of the neuromuscular junctions (NMJs). In model mice these synapses appear disorganized, fail to mature and are characterized by poorly arborized nerve terminals. Given one role of the SMN protein in orchestrating the assembly of spliceosomal snRNP particles and subsequently regulating the alternative splicing of pre-mRNAs, a plausible link between SMN function and the distal neuromuscular SMA phenotype is an incorrectly spliced transcript or transcripts involved in establishing or maintaining NMJ structure. In this study we explore the effects of one such transcript - Z+ Agrin - known to be a critical organizer of the NMJ. We confirm that low SMN protein reduces motor neuronal levels of Z+Agrin. Repletion of this isoform of Agrin in the motor neurons of SMA model mice increases muscle fiber size, enhances the post-synaptic NMJ area, reduces the abnormal accumulation of intermediate filaments in nerve terminals of the neuromuscular synapse and improves the innervation of muscles. While these effects are independent of changes in SMN levels or increases in motor neuron numbers they nevertheless have a significant effect on the overall disease phenotype, enhancing mean survival in severely affected SMA model mice by ∼40%. We conclude that Agrin is an important target of the SMN protein and that mitigating NMJ defects may be one strategy in treating human spinal muscular atrophy.
Pub.: 06 Apr '17, Pinned: 27 Jun '17
Abstract: The adult mammalian heart is non-regenerative due to the post-mitotic nature of cardiomyocytes. The neonatal mouse heart can regenerate, but only for the first week of life. Here we show that changes in the composition of the extracellular matrix (ECM) during this week can affect cardiomyocyte growth and differentiation in mice. We identify Agrin, a component of neonatal ECM, as required for the full regenerative capacity of neonatal mouse hearts. In vitro, recombinant Agrin promotes the division of mouse and human iPSC-derived cardiomyocytes via a mechanism that involves the disassembly of the dystrophin glycoprotein complex and Yap and ERK-mediated signaling. In vivo, a single administration of Agrin promotes cardiac regeneration in adult mice after myocardial infarction, although the degree of cardiomyocyte proliferation observed in this model suggests additional therapeutic mechanisms. Collectively, we uncover a new inducer of mammalian heart regeneration, highlighting fundamental roles of the ECM in cardiac repair.
Pub.: 06 Jun '17, Pinned: 27 Jun '17
Abstract: Growth factor (GF) signaling is a key determinant of stem cell fate. Interactions of GFs with their receptors are often mediated by heparan sulfate proteoglycans (HSPGs). Here, we report a cell surface engineering strategy that exploits the function of HSPGs to promote differentiation in embryonic stem cells (ESCs). We have generated synthetic neoproteoglycans (neoPGs) with affinity for the fibroblast growth factor 2 (FGF2) and introduced them into plasma membranes of ESCs deficient in HS biosynthesis. There, the neoPGs assumed the function of native HSPGs, rescued FGF2-mediated kinase activity, and promoted neural specification. This glycocalyx remodeling strategy is versatile and may be applicable to other types of differentiation.
Pub.: 16 Jul '14, Pinned: 27 Jun '17
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