Dr. Sarah  Hewitt   image

Dr. Sarah Hewitt

4009 Orchard Dr
Midland MI 48640
989 393-3515
Medical School: Other - Unknown
Accepts Medicare: No
Participates In eRX: No
Participates In PQRS: No
Participates In EHR: No
License #: 4301106045
NPI: 1891109930
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Structure-guided design and optimization of small molecules targeting the protein-protein interaction between the von Hippel-Lindau (VHL) E3 ubiquitin ligase and the hypoxia inducible factor (HIF) alpha subunit with in vitro nanomolar affinities. - Journal of medicinal chemistry
E3 ubiquitin ligases are attractive targets in the ubiquitin-proteasome system, however, the development of small-molecule ligands has been rewarded with limited success. The von Hippel-Lindau protein (pVHL) is the substrate recognition subunit of the VHL E3 ligase that targets HIF-1α for degradation. We recently reported inhibitors of the pVHL:HIF-1α interaction, however they exhibited moderate potency. Herein, we report the design and optimization, guided by X-ray crystal structures, of a ligand series with nanomolar binding affinities.
Diagnostic whole genome sequencing and split-read mapping for nucleotide resolution breakpoint identification in CNTNAP2 deficiency syndrome. - American journal of medical genetics. Part A
Whole genome sequencing (WGS) has the potential to report on all types of genetic abnormality, thus converging diagnostic testing on a single methodology. Although WGS at sufficient depth for robust detection of point mutations is still some way from being affordable for diagnostic purposes, low-coverage WGS is already an excellent method for detecting copy number variants ("CNVseq"). We report on a family in which individuals presented with a presumed autosomal recessive syndrome of severe intellectual disability and epilepsy. Array comparative genomic hybridization (CGH) analysis had revealed a homozygous deletion apparently lying within intron 3 of CNTNAP2. Since this was too small for confirmation by FISH, CNVseq was used, refining the extent of this mutation to approximately 76.8 kb, encompassing CNTNAP2 exon 3 (an out-of-frame deletion). To characterize the precise breakpoints and provide a rapid molecular diagnostic test, we resequenced the CNVseq library at medium coverage and performed split read mapping. This yielded information for a multiplex polymerase chain reaction (PCR) assay, used for cascade screening and/or prenatal diagnosis in this family. This example demonstrates a rapid, low-cost approach to converting molecular cytogenetic findings into robust PCR-based tests.© 2014 Wiley Periodicals, Inc.
Measuring the quality of surgical decisions for Latina breast cancer patients. - Health expectations : an international journal of public participation in health care and health policy
A high-quality decision for breast cancer surgery requires that patients are well informed, meaningfully involved in decision making, and receive treatments that match their goals. There is little in the existing literature that examines a comprehensive measure of decision quality for Latina breast cancer patients.To examine the quality of surgical decisions among Latina breast cancer survivors and explore factors associated with decision quality and decision regret.Cross-sectional mailed survey.English and certified Spanish translations of Breast Cancer Surgery Decision Quality Instrument (BCS-DQI), Short Acculturation Scale for Hispanics (SASH) and decision regret.Ninety-seven breast cancer survivors of Hispanic or Spanish descent identified through the cancer registry from Orange or San Diego Counties in California.The 97 respondents were on average 55.7 years old, 39.1% had high school diploma or more education, and 62.9% had low acculturation (SASH scores < 2.99). The average knowledge score was 48.2%, the average decision process score was 67.5%, and many (77.3%) received treatments that matched their goals. In multivariable models, there were no significant associations with education, age, acculturation and any aspect of decision quality or decision regret in this sample. Respondents who had higher decision process scores, indicating more involvement in decision making, had significantly lower decision regret.The BCS-DQI may require some adaptation for Latina populations to improve acceptability. The different aspects of decision quality, including knowledge, decision process and concordance, did not vary by level of acculturation.© 2014 John Wiley & Sons Ltd.
Sequencing and characterisation of rearrangements in three S. pastorianus strains reveals the presence of chimeric genes and gives evidence of breakpoint reuse. - PloS one
Gross chromosomal rearrangements have the potential to be evolutionarily advantageous to an adapting organism. The generation of a hybrid species increases opportunity for recombination by bringing together two homologous genomes. We sought to define the location of genomic rearrangements in three strains of Saccharomyces pastorianus, a natural lager-brewing yeast hybrid of Saccharomyces cerevisiae and Saccharomyces eubayanus, using whole genome shotgun sequencing. Each strain of S. pastorianus has lost species-specific portions of its genome and has undergone extensive recombination, producing chimeric chromosomes. We predicted 30 breakpoints that we confirmed at the single nucleotide level by designing species-specific primers that flank each breakpoint, and then sequencing the PCR product. These rearrangements are the result of recombination between areas of homology between the two subgenomes, rather than repetitive elements such as transposons or tRNAs. Interestingly, 28/30 S. cerevisiae-S. eubayanus recombination breakpoints are located within genic regions, generating chimeric genes. Furthermore we show evidence for the reuse of two breakpoints, located in HSP82 and KEM1, in strains of proposed independent origin.
Progressive dopaminergic cell loss with unilateral-to-bilateral progression in a genetic model of Parkinson disease. - Proceedings of the National Academy of Sciences of the United States of America
DJ-1 mutations cause autosomal recessive early-onset Parkinson disease (PD). We report a model of PD pathology: the DJ1-C57 mouse. A subset of DJ-1-nullizygous mice, when fully backcrossed to a C57BL/6 [corrected] background, display dramatic early-onset unilateral loss of dopaminergic (DA) neurons in their substantia nigra pars compacta, progressing to bilateral degeneration of the nigrostriatal axis with aging. In addition, these mice exhibit age-dependent bilateral degeneration at the locus ceruleus nucleus and display mild motor behavior deficits at aged time points. These findings effectively recapitulate the early stages of PD. Therefore, the DJ1-C57 mouse provides a tool to study the preclinical aspects of neurodegeneration. Importantly, by exome sequencing, we identify candidate modifying genes that segregate with the phenotype, providing potentially critical clues into how certain genes may influence the penetrance of DJ-1-related degeneration in mice.
ROS-dependent regulation of Parkin and DJ-1 localization during oxidative stress in neurons. - Human molecular genetics
Mutations in several genes, including Parkin, PTEN-induced kinase 1 (Pink1) and DJ-1, are associated with rare inherited forms of Parkinson's disease (PD). Despite recent attention on the function of these genes, the interplay between DJ-1, Pink1 and Parkin in PD pathogenesis remains unclear. In particular, whether these genes regulate mitochondrial control pathways in neurons is highly controversial. Here we report that Pink1-dependent Parkin translocation does occur in mouse cortical neurons in response to a variety of mitochondrial damaging agents. This translocation only occurs in the absence of antioxidants in the neuronal culturing medium, implicating a key role of reactive oxygen species (ROS) in this response. Consistent with these observations, ROS blockers also prevent Parkin recruitment in mouse embryonic fibroblasts. Loss of DJ-1, a gene linked to ROS management, results in increased stress-induced Parkin recruitment and increased mitophagy. Expression of wild-type DJ-1, but not a cysteine-106 mutant associated with defective ROS response, rescues this accelerated Parkin recruitment. Interestingly, DJ-1 levels increase at mitochondria following oxidative damage in both fibroblasts and neurons, and this process also depends on Parkin and possibly Pink1. These results not only highlight the presence of a Parkin/Pink1-mediated pathway of mitochondrial quality control (MQC) in neurons, they also delineate a complex reciprocal relationship between DJ-1 and the Pink1/Parkin pathway of MQC.
DJ-1 protects the nigrostriatal axis from the neurotoxin MPTP by modulation of the AKT pathway. - Proceedings of the National Academy of Sciences of the United States of America
Loss-of-function DJ-1 (PARK7) mutations have been linked with a familial form of early onset Parkinson disease. Numerous studies have supported the role of DJ-1 in neuronal survival and function. Our initial studies using DJ-1-deficient neurons indicated that DJ-1 specifically protects the neurons against the damage induced by oxidative injury in multiple neuronal types and degenerative experimental paradigms, both in vitro and in vivo. However, the manner by which oxidative stress-induced death is ameliorated by DJ-1 is not completely clear. We now present data that show the involvement of DJ-1 in modulation of AKT, a major neuronal prosurvival pathway induced upon oxidative stress. We provide evidence that DJ-1 promotes AKT phosphorylation in response to oxidative stress induced by H(2)O(2) in vitro and in vivo following 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) treatment. Moreover, we show that DJ-1 is necessary for normal AKT-mediated protective effects, which can be bypassed by expression of a constitutively active form of AKT. Taken together, these data suggest that DJ-1 is crucial for full activation of AKT upon oxidative injury, which serves as one explanation for the protective effects of DJ-1.
Altered chloride homeostasis removes synaptic inhibitory constraint of the stress axis. - Nature neuroscience
In mammals, stress elicits a stereotyped endocrine response that requires an increase in the activity of hypothalamic parvocellular neuroendocrine neurons. The output of these cells is normally constrained by powerful GABA-mediated synaptic inhibition. We found that acute restraint stress in rats released the system from inhibitory synaptic drive in vivo by down-regulating the transmembrane anion transporter KCC2. This manifested as a depolarizing shift in the reversal potential of GABA(A)-mediated synaptic currents that rendered GABA inputs largely ineffective. Notably, repetitive activation of GABA synapses after stress resulted in a more rapid collapse of the anion gradient and was sufficient to increase the activity of neuroendocrine cells. Our data indicate that hypothalamic neurons integrate psychological cues to mount the endocrine response to stress by regulating anion gradients.
Brain-derived neurotrophic factor silences GABA synapses onto hypothalamic neuroendocrine cells through a postsynaptic dynamin-mediated mechanism. - Journal of neurophysiology
In the paraventricular nucleus of the hypothalamus (PVN), experimental stress paradigms that suppress gamma-aminobutyric acid (GABA) inputs to parvocellular neuroendocrine cells (PNCs) also increase the expression of brain-derived neurotrophic factor (BDNF). In the adult CNS, BDNF regulates the efficacy of GABAergic transmission, but its contributions to functional changes at inhibitory synapses in the PVN have not been investigated. Analysis of quantal transmission revealed a decrease in the frequency of miniature inhibitory postsynaptic currents (mIPSCs) in response to BDNF with no accompanying changes in their amplitude. These effects were completely blocked by prior inclusion of the TrKB receptor antagonist K252a in the patch pipette. Inclusion of a dynamin inhibitory peptide in the patch pipette also blocked the effects of BDNF, consistent with an all-or-none removal of clusters of postsynaptic GABAA receptors. Finally, to confirm a decrease in the availability of postsynaptic GABAA receptors, we tested the effects of BDNF on focal application of the GABAA agonist muscimol. Postsynaptic responses to muscimol were reduced after BDNF. Collectively, these data indicate that BDNF remodels functional synaptic contacts putatively by reducing the surface expression of postsynaptic GABAA receptors.
Norepinephrine triggers release of glial ATP to increase postsynaptic efficacy. - Nature neuroscience
Glial cells actively participate in synaptic transmission. They clear molecules from the synaptic cleft, receive signals from neurons and, in turn, release molecules that can modulate signaling between neuronal elements. Whether glial-derived transmitters can contribute to enduring changes in postsynaptic efficacy, however, remains to be established. In rat hypothalamic paraventricular nucleus, we demonstrate an increase in the amplitude of miniature excitatory postsynaptic currents in response to norepinephrine that requires the release of ATP from glial cells. The increase in quantal efficacy, which likely results from an insertion of AMPA receptors, is secondary to the activation of P2X(7) receptors, an increase in postsynaptic calcium and the activation of phosphatidylinositol 3-kinase. The gliotransmitter ATP, therefore, contributes directly to the regulation of postsynaptic efficacy at glutamatergic synapses in the CNS.

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