Angiogenesis is the formation of new capillaries from pre-existing blood vessels and participates in proper vasculature development. In pathological conditions such as cancer, abnormal angiogenesis takes place. Angiogenesis is primarily carried out by endothelial cells, the innermost layer of blood vessels. The vascular endothelial growth factor-A (VEGF-A) and its receptor-2 (VEGFR-2) trigger most of the mechanisms activating and regulating angiogenesis, and have been the targets for the development of drugs. However, most experimental assays assessing angiogenesis rely on animal models. We report an in vitro model using a microvessel-on-a-chip. It mimics an effective endothelial sprouting angiogenesis event triggered from an initial microvessel using a single angiogenic factor, VEGF-A. The angiogenic sprouting in this model is depends on the Notch signaling, as observed in vivo. This model enables the study of anti-angiogenic drugs which target a specific factor/receptor pathway, as demonstrated by the use of the clinically approved sorafenib and sunitinib for targeting the VEGF-A/VEGFR-2 pathway. Furthermore, this model allows testing simultaneously angiogenesis and permeability. It demonstrates that sorafenib impairs the endothelial barrier function, while sunitinib does not. Such in vitro human model provides a significant complimentary approach to animal models for the development of effective therapies.

Methionine sulfoxide reductase B3 (MsrB3) is a protein repair enzyme that specifically reduces methionine-R-sulfoxide to methionine. A recent genetic study showed that the MSRB3 gene is associated with autosomal recessive hearing loss in human deafness DFNB74. However, the precise role of MSRB3 in the auditory system and the pathogenesis of hearing loss have not yet been determined. This work is the first to generate MsrB3 knockout mice to elucidate the possible pathological mechanisms of hearing loss observed in DFNB74 patients. We found that homozygous MsrB3(-/-) mice were profoundly deaf and had largely unaffected vestibular function, whereas heterozygous MsrB3(+/-) mice exhibited normal hearing similar to that of wild-type mice. The MsrB3 protein is expressed in the sensory epithelia of the cochlear and vestibular tissues, beginning at E15.5 and E13.5, respectively. Interestingly, MsrB3 is densely localized at the base of stereocilia on the apical surface of auditory hair cells. MsrB3 deficiency led to progressive degeneration of stereociliary bundles starting at P8, followed by a loss of hair cells, resulting in profound deafness in MsrB3(-/-) mice. The hair cell loss appeared to be mediated by apoptotic cell death, which was measured using TUNEL and caspase 3 immunocytochemistry. Taken together, our data suggest that MsrB3 plays an essential role in maintaining the integrity of hair cells, possibly explaining the pathogenesis of DFNB74 deafness in humans caused by MSRB3 deficiency.

Aims: Methionine sulfoxide reductase A (MsrA) and methionine metabolism are associated with oxidative stress, a principal cause of ischemia/reperfusion (I/R) injury. Herein, we investigated the protective role of MsrA against kidney I/R injury and the involvement of MsrA in methionine metabolism and the transsulfuration pathway during I/R. Results: We found that MsrA gene-deleted mice (MsrA -/ -) were more susceptible to kidney I/R injury than wild-type mice (MsrA +/+ ). Deletion of MsrA enhanced renal functional and morphological impairments, congestion, inflammatory responses, and oxidative stress under I/R conditions. Concentrations of homocysteine and H 2 S in the plasma of control MsrA -/ -mice were significantly lower than those in control MsrA +/+ mice. I/R reduced the levels of homocysteine and H 2 S in both MsrA +/+ and MsrA -/ -mice, and these reductions were significantly more profound in MsrA -/ -than in MsrA +/+ mice. I/R reduced the expression and activities of cystathionine-b-synthase (CBS) and cystathionine-c-lyase (CSE), both of which are H 2 S-producing enzymes, in the kidneys. These reductions were more profound in the MsrA -/ -mice than in the MsrA +/+ mice. Innovation: The data provided herein constitute the first in vivo evidence for the involvement of MsrA in regulating methionine metabolism and the trans-sulfuration pathway under normal and I/R conditions. Conclusion: Our data demonstrate that MsrA protects the kidney against I/R injury, and that this protection is associated with reduced oxidative stress and inflammatory responses. The data indicate that MsrA regulates H 2 S production during I/R by modulating the expression and activity of the CBS and CSE enzymes.

A 3D in vitro microvessel model consisting of pericytes and endothelial cells which enables visualization of the multistep process of angiogenesis induced by VEGF.

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