Regulation of Microtubule Organization and Microtubule-dependent Transport by Septin 9

Microtubules (MTs) are a major component of the mammalian cytoskeleton. MTs are essential for cell morphogenesis and cellular functions including cell motility, cell division and intra-cellular transport. MT functions are tightly regulated by post-translational modifications (PTMs) and MT-associated proteins (MAPs). However, the underlying mechanisms are still elusive. Septins are a family of GTP-binding proteins that can form hetero-oligomeric and polymeric structures, and function as scaffolds or diffusion barriers, controlling the localization of membrane and cytoplasmic proteins. Mammalian septins interact with MTs and actin filaments, Septins are also involved in Golgi-to-plasma membrane vesicle transport and chromosome alignment. Interestingly, septins have been shown to interact with the centromere-associated protein E (CENP-E), a mitotic kinesin-like motor that links kinetochores to the ends of spindle MTs. However, it is unknown whether septins interact directly with MTs and how they affect MT organization and intracellular transport. In the first part of this thesis, I studied how MT organization is regulated by septins. I showed that the N-terminal domain of SEPT9 contains the novel repeat motifs K/R-x-x-E/D and R/K-R-x-E, which bind and bundle MTs by interacting with the acidic C-terminal tails of [beta]-tubulin. Alanine scanning mutagenesis revealed that the K/R-R/x-x-E/D motifs pair electrostatically with one another and the C-terminal tails of β-tubulin, enabling septin-septin interactions that link MTs together. SEPT9 is the only gene linked to hereditary neuralgic amyotrophy (HNA), a rare autosomal-dominant neuropathy. SEPT9 isoforms lacking repeat motifs or containing the HNA-linked mutation R88W, which maps to the R/K-R-x-E motif, diminished intracellular MT bundling and impaired asymmetric neurite growth in PC-12 cells. These findings provide the first insight into the mechanism of septin interaction with MTs and the molecular and cellular basis of HNA. In the second part of this thesis, I discovered a novel interaction between SEPT9 and KIF17, a kinesin 2 family motor that is important for learning and memory, mediating the transport of the NMDA glutamate receptor in hippocampal neurons. I found that SEPT9 associates directly with the cargo-binding C-terminal tail of KIF17 and competes with mLin-10/Mint1, a cargo adaptor/scaffold protein, which links KIF17 to the NMDA receptor subunit 2B (NR2B). Significantly, SEPT9 down-regulates NR2B transport into the dendrites of hippocampal neurons. Because SEPT9 does not affect the microtubule-dependent motility of KIF17, my results suggest that SEPT9 modulates the interaction of KIF17 with NR2B cargo. These results provide the first evidence of an interaction between septins and a non-mitotic kinesin, and suggest that SEPT9 modulates specifically the interactions of KIF17 with membrane cargo. These findings advanced our knowledge of how septins associate with MTs and revealed the mechanism of MT binding and bundling by septins. My studies also provided the first clue about the etiology of HNA, which might be helpful in developing therapies for this disease in the future. In addition, the results of this work provided the first insight into how septins may regulate kinesin-dependent transport and the transport of a neurotransmitter to dendrite membrane. This knowledge could potentially be helpful in developing treatment for diseases associated with misregulation of MT organization and MT based transport.Ph.D., Biological Sciences -- Drexel University, 201

VEGF Is Involved in the Increase of Dermal Microvascular Permeability Induced by Tryptase

Tryptases are predominantly mast cell-specific serine proteases with pleiotropic biological activities and play a critical role in skin allergic reactions, which are manifested with rapid edema and increases of vascular permeability. The exact mechanisms of mast cell tryptase promoting vascular permeability, however, are unclear and, therefore, we investigated the effect and mechanism of tryptase or human mast cells (HMC-1) supernatant on the permeability of human dermal microvascular endothelial cells (HDMECs). Both tryptase and HMC-1 supernatant increased permeability of HDMECs significantly, which was resisted by tryptase inhibitor APC366 and partially reversed by anti-VEGF antibody and SU5614 (catalytic inhibitor of VEGFR). Furthermore, addition of tryptase to HDMECs caused a significant increase of mRNA and protein levels of VEGF and its receptors (Flt-1 and Flk-1) by Real-time RT-PCR and Western blot, respectively. These results strongly suggest an important role of VEGF on the permeability enhancement induced by tryptase, which may lead to novel means of controlling allergic reaction in skin

Multi-contrast brain magnetic resonance image super-resolution using the local weight similarity

Abstract Background Low-resolution images may be acquired in magnetic resonance imaging (MRI) due to limited data acquisition time or other physical constraints, and their resolutions can be improved with super-resolution methods. Since MRI can offer images of an object with different contrasts, e.g., T1-weighted or T2-weighted, the shared information between inter-contrast images can be used to benefit super-resolution. Methods In this study, an MRI image super-resolution approach to enhance in-plane resolution is proposed by exploring the statistical information estimated from another contrast MRI image that shares similar anatomical structures. We assume some edge structures are shown both in T1-weighted and T2-weighted MRI brain images acquired of the same subject, and the proposed approach aims to recover such kind of structures to generate a high-resolution image from its low-resolution counterpart. Results The statistical information produces a local weight of image that are found to be nearly invariant to the image contrast and thus this weight can be used to transfer the shared information from one contrast to another. We analyze this property with comprehensive mathematics as well as numerical experiments. Conclusion Experimental results demonstrate that the image quality of low-resolution images can be remarkably improved with the proposed method if this weight is borrowed from a high resolution image with another contrast. Graphical Abstract Multi-contrast MRI Image Super-resolution with Contrast-invariant Regression Weight

Crustal structure beneath the Indochina peninsula from teleseismic receiver functions

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/95076/1/grl27455.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/95076/2/grl27455-sup-0012-ts01.pd

Pathological mechanisms of type 1 diabetes in children: investigation of the exosomal protein expression profile

IntroductionType 1 diabetes (T1D) is a serious autoimmune disease with high morbidity and mortality. Early diagnosis and treatment remain unsatisfactory. While the potential for development of T1D biomarkers in circulating exosomes has attracted interest, progress has been limited. This study endeavors to explore the molecular dynamics of plasma exosome proteins in pediatric T1D patients and potential mechanisms correlated with T1D progressionMethodsLiquid chromatography-tandem mass spectrometry with tandem mass tag (TMT)6 labeling was used to quantify exosomal protein expression profiles in 12 healthy controls and 24 T1D patients stratified by age (≤ 6 years old and > 6 years old) and glycated hemoglobin (HbA1c) levels (> 7% or > 7%). Integrated bioinformatics analysis was employed to decipher the functions of differentially expressed proteins, and Western blotting was used for validation of selected proteins' expression levels. ResultsWe identified 1035 differentially expressed proteins (fold change > 1.3) between the T1D patients and healthy controls: 558 in those ≤ 6-year-old and 588 in those > 6-year-old. In those who reached an HbA1c level < 7% following 3 or more months of insulin therapy, the expression levels of most altered proteins in both T1D age groups returned to levels comparable to those in the healthy control group. Bioinformatics analysis revealed that differentially expressed exosome proteins are primarily related to immune function, hemostasis, cellular stress responses, and matrix organization. Western blotting confirmed the alterations in RAB40A, SEMA6D, COL6A5, and TTR proteins. DiscussionThis study delivers valuable insights into the fundamental molecular mechanisms contributing to T1D pathology. Moreover, it proposes potential therapeutic targets for improved T1D management