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Integrative transcriptomic and proteomic analysis of osteocytic cells exposed to fluid flow reveals novel mechano-sensitive signaling pathways.

ABSTRACT: Osteocytes, positioned within bone?s porous structure, are subject to interstitial fluid flow upon whole bone loading. Such fluid flow is widely theorized to be a mechanical signal transduced by osteocytes, initiating a poorly understood cascade of signaling events mediating bone adaptation to mechanical load. The objective of this study was to examine the time course of flow-induced changes in osteocyte gene transcript and protein levels using high-throughput approaches. Osteocyte-like MLO-Y4 cells were subjected to 2h of oscillating fluid flow (1Pa peak shear stress) and analyzed following 0, 2, 8, and 24h post-flow incubation. Transcriptomic microarray analysis, followed by gene ontology pathway analysis, demonstrated fluid flow regulation of genes consistent with both known and unknown metabolic and inflammatory responses in bone. Additionally, two of the more highly up-regulated gene products - chemokines Cxcl1 and Cxcl2, supported by qPCR - have not previously been reported as responsive to fluid flow. Proteomic analysis demonstrated greatest up-regulation of the ATP-producing enzyme NDK, calcium-binding Calcyclin, and G protein-coupled receptor kinase 6. Finally, an integrative pathway analysis merging fold changes in transcript and protein levels predicted signaling nodes not directly detected at the sampled time points, including transcription factors c-Myc, c-Jun, and RelA/NF-?B. These results extend our knowledge of the osteocytic response to fluid flow, most notably up-regulation of Cxcl1 and Cxcl2 as possible paracrine agents for osteoblastic and osteoclastic recruitment. Moreover, these results demonstrate the utility of integrative, high-throughput approaches in place of a traditional candidate approach for identifying novel mechano-sensitive signaling molecules.

SUBMITTER: Govey PM

PROVIDER: S-EPMC4037855 | biostudies-literature | 2014 Jun

REPOSITORIES: biostudies-literature

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Integrative transcriptomic and proteomic analysis of osteocytic cells exposed to fluid flow reveals novel mechano-sensitive signaling pathways.

Govey Peter M PM Jacobs Jon M JM Tilton Susan C SC Loiselle Alayna E AE Zhang Yue Y Freeman Willard M WM Waters Katrina M KM Karin Norman J NJ Donahue Henry J HJ

Journal of biomechanics 20140325 8

Osteocytes, positioned within bone׳s porous structure, are subject to interstitial fluid flow upon whole bone loading. Such fluid flow is widely theorized to be a mechanical signal transduced by osteocytes, initiating a poorly understood cascade of signaling events mediating bone adaptation to mechanical load. The objective of this study was to examine the time course of flow-induced changes in osteocyte gene transcript and protein levels using high-throughput approaches. Osteocyte-like MLO-Y4 c ...[more]

PMID: 24720889

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Project description:Atherosclerosis preferentially occurs in arterial regions of disturbed blood flow (d-flow), which alters gene expression, endothelial function, and atherosclerosis. Here, we show that d-flow regulates genome-wide DNA methylation patterns in a DNA methyltransferase (DNMT)-dependent manner. D-flow induced expression of DNMT1 in mouse arterial endothelium in vivo and in cultured endothelial cells by oscillatory shear (OS) in vitro. The DNMT inhibitor 5-Aza-2’deoxycytidine (5Aza) or DNMT1 siRNA significantly reduced OS-induced endothelial inflammation. Moreover, 5Aza reduced lesion formation in two ApoE-/- mouse atherosclerosis models. To identify the 5Aza mechanisms, we conducted two genome-wide studies: reduced representation bisulfite sequencing (RRBS) and microarray using endothelial-enriched gDNA and RNA, respectively, from the partially-ligated left carotid artery (LCA exposed to d-flow) and the right contralateral control (RCA) of mice treated with 5Aza or vehicle. Systems biological analyses using RRBS and transcriptome data revealed 11 mechanosensitive genes whose promoters were hypermethylated under d-flow conditions, but rescued by 5Aza treatment. Of those, the two transcription factors HoxA5 and Klf3 contain cAMP- response-elements, and their methylation status could serve as a mechanosensitive master switch in gene expression. Our results demonstrate that d-flow controls epigenomic DNA methylation patterns in a DNMT-dependent manner, which in turn alters endothelial gene expression and induces atherosclerosis. We used 6- to 8-week-old male C57Bl/6 mice (The Jackson Laboratory) according to the approved Institutional Animal Care and Use Committee protocol by Emory University. Mice were subjected to partial carotid ligation surgery under anesthesia. Brieﬂy, 3 of 4 caudal branches of LCA (left external carotid, internal carotid, and occipital artery) were ligated with 6-0 silk suture, although the superior thyroid artery was left intact. Development of low and oscillatory blood flow in the Left Carotid Artery of each mouse was determined by ultrasound measurements. Each sample contained total RNA from 3 pooled RCAs or LCAs. We ran 3 samples of LCA, RCA, AzaLCA, and AzaRCA on 2 microarrays.

Dataset Information

Integrative transcriptomic and proteomic analysis of osteocytic cells exposed to fluid flow reveals novel mechano-sensitive signaling pathways.

Publications

Integrative transcriptomic and proteomic analysis of osteocytic cells exposed to fluid flow reveals novel mechano-sensitive signaling pathways.

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