Yuli Liu

Washington University in St. Louis, San Luis, Missouri, United States

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Publications (13)55.55 Total impact

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    ABSTRACT: Mucopolysaccharidosis VII (MPS VII) is due to the deficient activity of β-glucuronidase (GUSB) and results in the accumulation of glycosaminoglycans (GAGs) in lysosomes and multisystemic disease with cardiovascular manifestations. The goal here was to determine the pathogenesis of mitral valve (MV) disease in MPS VII dogs. Untreated MPS VII dogs had a marked reduction in the histochemical signal for structurally-intact collagen in the MV at 6months of age, when mitral regurgitation had developed. Electron microscopy demonstrated that collagen fibrils were of normal diameter, but failed to align into large parallel arrays. mRNA analysis demonstrated a modest reduction in the expression of genes that encode collagen or collagen-associated proteins such as the proteoglycan decorin which helps collagen fibrils assemble, and a marked increase for genes that encode proteases such as cathepsins. Indeed, enzyme activity for cathepsin B (CtsB) was 19-fold normal. MPS VII dogs that received neonatal intravenous injection of a gamma retroviral vector had an improved signal for structurally-intact collagen, and reduced CtsB activity relative to that seen in untreated MPS VII dogs. We conclude that MR in untreated MPS VII dogs was likely due to abnormalities in MV collagen structure. This could be due to upregulation of enzymes that degrade collagen or collagen-associated proteins, to the accumulation of GAGs that compete with proteoglycans such as decorin for binding to collagen, or to other causes. Further delineation of the etiology of abnormal collagen structure may lead to treatments that improve biomechanical properties of the MV and other tissues.
    Molecular Genetics and Metabolism 06/2013; · 2.83 Impact Factor
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    ABSTRACT: Mucopolysaccharidosis VII (MPS VII) is due to deficient activity of the lysosomal enzyme β-glucuronidase (GUSB) and results in the accumulation of glycosaminoglycans (GAGs). This study determined the long-term effect of neonatal intravenous injection of a gamma retroviral vector (RV) on cardiac valve disease in MPS VII dogs. Transduced hepatocytes secreted GUSB into the blood for up to 11years at levels similar to or greater than those achieved with enzyme replacement therapy (ERT). Valve regurgitation and thickening were scored from 0 (normal) to +4 (severely abnormal). At 1year, untreated MPS VII dogs had mitral regurgitation, mitral valve thickening, aortic regurgitation, and aortic valve thickening scores of 2.3±0.7, 2.3±0.6, 1.8±0.5, and 1.6±0.7, respectively, which were higher than the values of 0.6±0.1, 0.1±0.4, 0.3±0.8, and 0.1±0.4, respectively, in treated MPS VII dogs. Treated MPS VII dogs maintained low aortic regurgitation and aortic valve thickening scores in their lifetime. Although mitral regurgitation and mitral valve thickening scores increased to 2.0 at ≥8years of age in the treated MPS VII dogs, older normal dogs from the colony had similar scores, making it difficult to assess mitral valve disease. Older treated dogs had calcification within the mitral and the aortic valve annulus, while GUSB staining demonstrated enzyme activity within the mitral valve. We conclude that neonatal RV-mediated gene therapy reduced cardiac valve disease in MPS VII dogs for up to 11years, and propose that neonatal initiation of ERT should have a similar effect.
    Molecular Genetics and Metabolism 06/2013; · 2.83 Impact Factor
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    ABSTRACT: Mucopolysaccharidosis (MPS) VII is a lysosomal storage disease due to deficient activity of β-glucuronidase (GUSB), and results in glycosaminoglycan accumulation. Skeletal manifestations include bone dysplasia, degenerative joint disease, and growth retardation. One gene therapy approach for MPS VII involves neonatal intravenous injection of a gamma retroviral vector expressing GUSB, which results in stable expression in liver and secretion of enzyme into blood at levels predicted to be similar or higher to enzyme replacement therapy. The goal of this study was to evaluate the long-term effect of neonatal gene therapy on skeletal manifestations in MPS VII dogs. Treated MPS VII dogs could walk throughout their lives, while untreated MPS VII dogs could not stand beyond 6months and were dead by 2years. Luxation of the coxofemoral joint and the patella, dysplasia of the acetabulum and supracondylar ridge, deep erosions of the distal femur, and synovial hyperplasia were reduced, and the quality of articular bone was improved in treated dogs at 6 to 11years of age compared with untreated MPS VII dogs at 2years or less. However, treated dogs continued to have osteophyte formation, cartilage abnormalities, and an abnormal gait. Enzyme activity was found near synovial blood vessels, and there was 2% as much GUSB activity in synovial fluid as in serum. We conclude that neonatal gene therapy reduces skeletal abnormalities in MPS VII dogs, but clinically-relevant abnormalities remain. Enzyme replacement therapy will probably have similar limitations long-term.
    Molecular Genetics and Metabolism 04/2013; · 2.83 Impact Factor
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    ABSTRACT: Mucopolysaccharidosis type VII (MPS VII) is characterized by deficient β-glucuronidase (GUSB) activity, which leads to accumulation of chondroitin, heparan and dermatan sulfate glycosaminoglycans (GAGs), and multisystemic disease. MPS VII patients can develop kypho-scoliotic deformity and spinal cord compression due to disease of intervertebral disks, vertebral bodies, and associated tissues. We have previously demonstrated in MPS VII dogs that intervertebral disks degenerate, vertebral bodies have irregular surfaces, and vertebral body epiphyses have reduced calcification, but the pathophysiological mechanisms underlying these changes are unclear. We hypothesized that some of these manifestations could be due to upregulation of destructive proteases, possibly via the binding of GAGs to Toll-like receptor 4 (TLR4), as has been proposed for other tissues in MPS models. In this study, the annulus fibrosus of the intervertebral disk of 6-month-old MPS VII dogs had cathepsin B and K activities that were 117- and 2-fold normal, respectively, which were associated with elevations in mRNA levels for these cathepsins as well as TLR4. The epiphyses of MPS VII dogs had a marked elevation in mRNA for the cartilage-associated gene collagen II, consistent with a developmental delay in the conversion of the cartilage to bone in this region. The spine obtained at autopsy from a young man with MPS VII exhibited similar increased cartilage in the vertebral bodies adjacent to the end plates, disorganization of the intervertebral disks, and irregular vertebral end plate morphology. These data suggest that the pathogenesis of destructive changes in the spine in MPS VII may involve upregulation of cathepsins. Inhibition of destructive proteases, such as cathepsins, might reduce spine disease in patients with MPS VII or related disorders.
    Molecular Genetics and Metabolism 03/2012; 107(1-2):153-60. · 2.83 Impact Factor
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    ABSTRACT: Mucopolysaccharidosis VII (MPS VII) is due to mutations within the gene encoding the lysosomal enzyme β-glucuronidase, and results in the accumulation of glycosaminoglycans. MPS VII causes aortic dilatation and elastin fragmentation, which is associated with upregulation of the elastases cathepsin S (CtsS) and matrix metalloproteinase 12 (MMP12). To test the role of these enzymes, MPS VII mice were crossed with mice deficient in CtsS or MMP12, and the effect upon aortic dilatation was determined. CtsS deficiency did not protect against aortic dilatation in MPS VII mice, but also failed to prevent an upregulation of cathepsin enzyme activity. Further analysis with substrates and inhibitors specific for particular cathepsins suggests that this enzyme activity was due to CtsB, which could contribute to elastin fragmentation. Similarly, MMP12 deficiency and deficiency of both MMP12 and CtsS could not prevent aortic dilatation in MPS VII mice. Microarray and reverse-transcriptase real-time PCR were performed to look for upregulation of other elastases. This demonstrated that mRNA for complement component D was elevated in MPS VII mice, while immunostaining demonstrated high levels of complement component C3 on surfaces within the aortic media. Finally, we demonstrate that neonatal intravenous injection of a retroviral vector encoding β-glucuronidase reduced aortic dilatation. We conclude that neither CtsS nor MMP12 are necessary for elastin fragmentation in MPS VII mouse aorta, and propose that CtsB and/or complement component D may be involved. Complement may be activated by the GAGs that accumulate, and may play a role in signal transduction pathways that upregulate elastases.
    Molecular Genetics and Metabolism 08/2011; 104(4):608-19. · 2.83 Impact Factor
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    ABSTRACT: Mucopolysaccharidosis I (MPS I) is caused by deficient alpha-L-iduronidase (IDUA) activity and results in the accumulation of glycosaminoglycans and multisystemic disease. Gene therapy could program cells to secrete mannose 6-phosphate-modified IDUA, and enzyme in blood could be taken up by other cells. Neonatal retroviral vector (RV)-mediated gene therapy has been shown to reduce the manifestations of murine MPS I; however, intravenous injection of RV into adults was ineffective owing to a cytotoxic T lymphocyte (CTL) response against transduced cells. In this study, prolonged inhibition of CD28 signaling with CTLA4-Ig, or transient administration of CTLA4-Ig with an anti-CD40 ligand antibody or with an anti-CD4 antibody, resulted in stable expression in most mice that received RV as adults. Mice with stable expression had 81 +/- 41U/ml IDUA activity in serum. This resulted in reductions in bone disease, improvements in hearing and vision, and reductions in biochemical and pathological evidence of lysosomal storage in most organs. Improvements in brain were likely due to diffusion of enzyme from blood. However, aortic disease was refractory to treatment. This demonstrates that most manifestations of MPS I can be prevented using adult gene therapy if an immune response is blocked.
    Molecular Therapy 06/2007; 15(5):889-902. · 6.43 Impact Factor
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    ABSTRACT: Mucopolysaccharidosis I (MPS I) due to deficient alpha-L-iduronidase (IDUA) activity results in accumulation of glycosaminoglycans in many cells. Gene therapy could program cells to secrete IDUA modified with mannose 6-phosphate (M6P), and enzyme could be taken up by other cells via the M6P receptor. We previously reported that newborn MPS I mice that were injected intravenously with 10(9) (high-dose) or 10(8) (low-dose) transducing units/kg of a retroviral vector (RV) expressing canine IDUA achieved stable levels of IDUA activity in serum and had reduced disease in heart, eye, ear, and bone in a dose-dependent fashion. However, the dose required for improvement in manifestations of disease in other organs was not reported. High-dose and low-dose RV mice with an average serum IDUA activity of 1037+/-90 U/ml (471-fold normal) and 43+/-12 U/ml (20-fold normal), respectively, had complete correction of biochemical and pathological evidence of disease in the liver, spleen, kidney, and small intestines. Although mice that received high-dose RV had complete correction of lysosomal storage in thymus, ovary, lung, and testis, correction in these organs was only partial for those that received low-dose RV. Storage in brain was almost completely corrected with high-dose RV, but was not improved with low-dose RV. The correction of disease in brain may be due to diffusion of enzyme from blood. We conclude that high-dose RV prevents biochemical and pathological manifestations of disease in all organs in MPS I mice including brain.
    Molecular Genetics and Metabolism 03/2007; 90(2):181-92. · 2.83 Impact Factor
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    ABSTRACT: Mucopolysaccharidosis I (MPS I) is due to deficient activity of the 70 KD lysosomal enzyme α-L-iduronidase (IDUA) and results in an inability to degrade glycosaminoglycans in many cells. Severe MPS I results in cardiac disease, skeletal deformities, hearing and vision abnormalities, and mental retardation. We have previously reported that neonatal gene therapy with a high dose of a retroviral vector (RV) expressing canine IDUA resulted in stable expression and marked clinical improvements. However, since most patients with MPS I are not diagnosed at birth, it is necessary to test if gene therapy can be effective in older mice. However, a CTL responseoccurred after gene therapy to adults using the RV designated hAAT-cIDUA-WPRE for which the long terminal repeat (LTR) or the liver-specific human α1-antitrypsin promoter (hAAT) are in the same orientation. Although the liver is the major site of expression with this vector, expression also occurs at early times in spleen cells of an unknown phenotype. We hypothesized that an RV with liver-specific expression might avoid expression in antigen-presenting cells, and thus be unable to induce a CTL response. An RV was developed that contained a cassette with the hAAT promoter, a splice site, the canine IDUA cDNA, and a polyadenylation site in the opposite orientation to the LTR. This vector expressed IDUA activity well in HepG2 (human hepatoma) cells, but not in NIH 3T3 cells. This vector was injected IV into adults after hepatocyte replication was induced with hepatocyte growth factor (HGF). Transduced cells can secrete IDUA into blood, and serum IDUA activity reflects the stability of expression. Although serum IDUA expression was high at 1 week, it fell to low levels at 1 month. These data suggest that liver-restricted expression cannot prevent a CTL response against this lysosomal enzyme. We speculate that APCs might take up enzyme with M6P, and present its peptides. An alternative approach to prolong expression was to inhibit the immune system at the time of transfer of 1×109 transducing units/kg of hAAT-cIDUA-WPRE. CTLA4-Ig is an immunosuppressive agent that binds to CD80 and CD86 and prevents them from activating CD28, anti-CD4 antibody can deplete T cells, and anti-CD40 ligand can block co-stimulation. Although short-term administration of any agent alone did not result in long-term expression, prolonged CTLA4-Ig led to long-term (6.5 month) expression. Alternatively, 2 weeks of CTLA4-Ig combined with 2 days of anti-CD4 or with 2 days of anti-CD40 ligand led to long term expression. Mice that received adult gene transfer with successful immunomodulation had an average of 88+/−11 units (U)/ml of IDUA activity in serum. Bone mineral density and bone radiographs were normal (N=6), the a-wave of an electroretinograms was significantly improved (N=4), and 3 of 4 mice had improved echocardiograms. However, hearing was not improved (N=3). We conclude that adult gene therapy with short term immunomodulation can reduce some manifestations of disease in MPS I mice.
    Molecular Therapy 05/2006; 13. · 6.43 Impact Factor
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    ABSTRACT: Mucopolysaccharidosis I (MPS I) is a lysosomal storage disease (LSD) due to deficient á-L-iduronidase (IDUA) activity. Although neonatal gene therapy with a retroviral vector (RV) expressing canine IDUA (cIDUA) resulted in stable expression in most mice and marked improvement in clinical manifestations, most patients with MPS I are not diagnosed at birth. It will therefore be necessary to determine if gene therapy can be effective in older animals. Adult MPS I mice were transiently treated with hepatocyte growth factor at 6 weeks of age to induce hepatocyte replication, which was followed by injection of hAAT-cIDUA-WPRE during the period of hepatocyte replication. hAAT-cIDUA-WPRE is an amphotropic gamma RV with the liver-specific human á1-antitrypsin promoter upstream of the canine IDUA cDNA, although expression can also derive from the long terminal repeat of the RV in non-hepatic cells. Although most of the IDUA made by hepatocytes is transported to the lysosome after modification with mannose 6-phosphate, some enzyme is secreted into blood where it can be taken up by other organs. Eight mice achieved serum IDUA activity of 97 ±19 U/ml at 1 week after transduction. However, activity fell to
    Molecular Therapy 08/2005; 11. · 6.43 Impact Factor
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    ABSTRACT: Mucopolysaccharidosis I (MPS I) due to deficient alpha-L-iduronidase (IDUA) activity results in accumulation of glycosaminoglycans in many cells. Gene therapy could program liver to secrete enzyme with mannose 6-phosphate (M6P), and enzyme in blood could be taken up by other cells via the M6P receptor. Newborn MPS I mice were injected with 10(9) (high dose) or 10(8) (low dose) transducing units/kg of a retroviral vector (RV) expressing canine IDUA. Most animals achieved stable expression of IDUA in serum at 1240 +/- 147 and 110 +/- 31 units/ml, respectively. At 8 months, untreated MPS I mice had aortic insufficiency, increased bone mineral density (BMD), and reduced responses to sound and light. In contrast, MPS I mice that received high-dose RV had normal echocardiograms, BMD, auditory-evoked brain-stem responses, and electroretinograms. This is the first report of complete correction of these clinical manifestations in any model of mucopolysaccharidosis. Biochemical and pathologic evaluation confirmed that storage was reduced in these organs. Mice that received low-dose RV and achieved 30 units/ml of serum IDUA activity had no or only partial improvement. We conclude that high-dose neonatal gene therapy with an RV reduces some major clinical manifestations of MPS I in mice, but low dose is less effective.
    Molecular Therapy 02/2005; 11(1):35-47. · 6.43 Impact Factor
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    ABSTRACT: Mucopolysaccharidosis (MPS) is due to deficiencies in enzymes that degrade glycosaminoglycans (GAGs). MPS I is due to deficient α-L-iduronidase activity (IDUA) and results in the accumulation of heparin sulfate (HS) and dermatan sulfate (DS). MPS VII is due to deficient β-glucuronidase activity and results in the accumulation of chondroitin sulfate (CS) in addition to HS and DS. Both disorders result in dysostosis multiplex in patients, which is characterized by short and thick bones. MPS can be treated with liver-directed gene therapy in which hepatocytes continuously secrete enzyme with mannose 6-phosphate, which can be taken up from blood. Although hepatic gene therapy reduced many manifestations of MPS VII, bone disease has not been completely corrected. The purpose of this study was to evaluate the effect of neonatal retroviral vector (RV)-mediated gene therapy on bone disease in MPS I mice. In contrast to untreated MPS VII mice in which long bones have only 81% to 87% of normal length, untreated MPS I mice had normal bone lengths at 6 weeks and 8 months after birth. Normal lengths were likely due to the fact that untreated MPS I mice had much less lysosomal storage material than did MPS VII mice in cartilage cells of the growth plate, which plays a pivotal role in bone elongation. This is likely due to the fact that CS is the major GAG in chondrocytes, and CS only accumulates in MPS VII. For untreated MPS I mice, bone mineral density (BMD) was normal at 6 weeks, but markedly increased at 0.069 gm/cm2 at 8 months [normal is 0.054 (p < 0.0001)]. The long bones of untreated MPS I mice had an increased diameter and were sclerotic, and there was substantial storage in osteocytes. The canine IDUA cDNA was cloned into a retroviral vector (RV) with a strong liver promoter, and the RV was injected into newborn MPS I mice at a high [1 × 109 transducing units (TU)/kg] or a low (1 × 108 TU/kg) dose. This resulted in transduction of liver cells and stable serum IDUA activity in most animals for 8 months at 1241 ± 147 and 110 ± 31 units (U)/ml for the high and low dose animals, respectively. At 8 months, mice that received a high dose of RV had normal long bone diameters without sclerosis, normal BMD [0.054 gm/cm2 (p < 0.0001 vs. values in untreated MPS I)], and marked reduction in lysosomal storage in the osteocytes. Mice that received a low dose of RV had some increase in diameter and sclerosis of the long bones, although they were not as severe as untreated MPS I mice. Similarly, the BMD (0.060 gm/cm2) was partially increased. We conclude that bone disease is much less severe in untreated MPS I mice than in untreated MPS VII mice. This is likely due to the fact that CS does not accumulate in MPS I, and CS is high in cartilage and accumulates in MPS VII. However, MPS I mice still had marked thickening and sclerosis of the bone, which were prevented with a high dose of RV at birth. However, the low dose of RV was less effective. These data help to define the serum activity necessary to prevent bone disease in MPS I.
    Molecular Therapy 01/2004; 9. · 6.43 Impact Factor
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    ABSTRACT: Immune responses after gene therapy could include an antibody response that blocks the activity of a blood protein, or a cytotoxic T lymphocyte (CTL) response that destroys transduced cells. Either could reduce the efficacy of gene therapy. We have previously shown that high dose neonatal gene therapy resulted in tolerance to canine Factor IX (cFIX), human FIX (hFIX), and canine β-glucuronidase in mice. However, since large animals may have a more mature immune system at birth, we evaluated immune responses after neonatal gene therapy in dogs and cats. Neonatal normal dogs that were transduced with a medium (3 × 109 transducing units (TU)/kg) or a low (8 × 107 TU/kg) dose of an RV expressing hFIX achieved stable expression of hFIX for over 6 months at 494 +/− 132 ng/ml (10% of normal) and 26 +/− 12 ng/ml (0.5% of normal), respectively. None of the neonatal RV-treated dogs developed anti-hFIX IgG. Further, the low dose group did not develop antibodies after infusion of 10 doses of hFIX (30 IU/kg/dose, given once per week starting at 2 months after birth), and thus were truly tolerant. Similar results were obtained in one hemophilia B dog that was transduced with 3 × 109 TU/kg of RV at birth and achieved 220 ng/ml of hFIX, as he did not develop anti-hFIX antibodies either before or after stimulation. In contrast, normal dogs that did not receive neonatal gene therapy developed high levels of anti-hFIX antibodies in response to an identical regimen of hFIX protein infusion. We conclude that neonatal gene therapy results in tolerance to hFIX in dogs. A similar gene therapy approach was tested in cats with mucopolysaccharidosis I (MPS I). Six MPS I cats received 1 × 109 TU/kg of an RV expressing canine α-L-iduronidase (IDUA) shortly after birth. All achieved detectable IDUA activity in blood within 2 weeks after gene transfer, with average serum levels of 25.2 units (U)/ml. However, serum activity declined to undetectable levels (
    Molecular Therapy 01/2004; 9. · 6.43 Impact Factor
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    ABSTRACT: Mucopolysaccharidosis (MPS) VI is a lysosomal storage disease caused by deficient activity of N-acetylgalactosamine 4-sulfatase (4S) resulting in an inability to degrade the glycosaminoglycan (GAG) dermatan sulfate, which accumulates in the lysosomes. Clinical features include skeletal abnormalities, growth retardation, facial dysmorphia, and corneal clouding. Two MPS VI cats were injected intravenously at 4 days of age with a Moloney murine leukemia virus-based retroviral vector containing the human alpha-1-antitrypsin promoter, the feline 4S (f4S) cDNA (kindly provided by John J. Hopwood), and the woodchuck hepatitis virus posttranscriptional regulatory element. Both animals received 7.2X10E9 transducing units/kg of body weight. Stable f4S activity has been detected in serum throughout the study and the most recent values from samples taken at 6 months were 23 and 9 times normal. The f4S activities in liver biopsies taken at 5 months were 82 and 38 times normal and the concentration of GAG in the biopsies was reduced to normal levels, 1.2 and 1.8 ug/mg protein, respectively. In comparison, the GAG concentration in liver biopsies from the untreated MPS VI littermates was 34.9 and 20.6 ug/mg. The body weights of the treated cats are 130% and 122% that of their two untreated MPS VI sex-matched control littermates (average of 1.89 kg) and are not different from normal unrelated age- and sex-matched controls. There are profound differences in the appearance of the treated and untreated cats. The MPS VI controls have short ears and tails and their faces are broad and flat. They have joint stiffness and major locomotor difficulties. The treated cats have only mild facial dysmorphia, a much freer range of pelvic motion, near normal gaits, and are more physically active than their MPS VI littermates. The cat with the higher f4S activity is nearly indistinguishable from a phenotypically normal cat except for the eyes, as there was no significant improvement in corneal clouding. MPS VI is particularly suited to liver-directed therapy because unlike other MPS disorders, CNS involvement is minimal. Because MPS VI is a progressive disease, the full extent of the clinical benefit will only become evident over time. We will present a 10-month update, including radiographs comparing the skeletons of normal, treated, and untreated MPS VI cats.
    Molecular Therapy - MOL THER. 01/2004; 9.

Publication Stats

151 Citations
55.55 Total Impact Points

Institutions

  • 2004–2013
    • Washington University in St. Louis
      • Department of Medicine
      San Luis, Missouri, United States
  • 2012
    • University of Pennsylvania
      • Department of Orthopaedic Surgery
      Philadelphia, PA, United States
  • 2005–2011
    • University of Washington Seattle
      • Division of General Internal Medicine
      Seattle, WA, United States