Connexin 43 Channels Protect Osteocytes Against Oxidative Stress–Induced Cell Death

Kar, Rekha; Riquelme, Manuel A.; Werner, Sherry L.; Jiang, Jean X.

doi:10.1002/jbmr.1917

Cited by 77 publications

(96 citation statements)

References 39 publications

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“…Similar to the current report, immunohistochemistry studies showed that Cx43 expression in osteocytes decreases in old mice (Kar et al ., 2013). On the other hand, the expression of Cx43 is not decreased in osteoblastic cells isolated from old rats (Genetos et al ., 2012).…”

Section: Discussionmentioning

confidence: 99%

“…In addition to increased osteocyte apoptosis, mice lacking osteocytic Cx43 (Cx43 ΔOt ) exhibit enhanced endocortical resorption, partially mimicking the phenotype of old mice (Almeida et al ., 2007b) and raising the possibility that decreased Cx43 contributes at least in part to the skeletal phenotype of aging. However, while it has been shown that Cx43 levels in osteocytes are decreased in old mice (Kar et al ., 2013), the signaling pathway activated by Cx43 deficiency involved in osteocyte apoptosis with aging is not known.…”

Section: Introductionmentioning

confidence: 99%

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Disruption of the Cx43/miR21 pathway leads to osteocyte apoptosis and increased osteoclastogenesis with aging

et al. 2017

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SummarySkeletal aging results in apoptosis of osteocytes, cells embedded in bone that control the generation/function of bone forming and resorbing cells. Aging also decreases connexin43 (Cx43) expression in bone; and osteocytic Cx43 deletion partially mimics the skeletal phenotype of old mice. Particularly, aging and Cx43 deletion increase osteocyte apoptosis, and osteoclast number and bone resorption on endocortical bone surfaces. We examined herein the molecular signaling events responsible for osteocyte apoptosis and osteoclast recruitment triggered by aging and Cx43 deficiency. Cx43‐silenced MLO‐Y4 osteocytic (Cx43def) cells undergo spontaneous cell death in culture through caspase‐3 activation and exhibit increased levels of apoptosis‐related genes, and only transfection of Cx43 constructs able to form gap junction channels reverses Cx43def cell death. Cx43def cells and bones from old mice exhibit reduced levels of the pro‐survival microRNA miR21 and, consistently, increased levels of the miR21 target phosphatase and tensin homolog (PTEN) and reduced phosphorylated Akt, whereas PTEN inhibition reduces Cx43def cell apoptosis. miR21 reduction is sufficient to induce apoptosis of Cx43‐expressing cells and miR21 deletion in miR21fl/fl bones increases apoptosis‐related gene expression, whereas a miR21 mimic prevents Cx43def cell apoptosis, demonstrating that miR21 lies downstream of Cx43. Cx43def cells release more osteoclastogenic cytokines [receptor activator of NFκB ligand (RANKL)/high‐mobility group box‐1 (HMGB1)], and caspase‐3 inhibition prevents RANKL/HMGB1 release and the increased osteoclastogenesis induced by conditioned media from Cx43def cells, which is blocked by antagonizing HMGB1‐RAGE interaction. These findings identify a novel Cx43/miR21/HMGB1/RANKL pathway involved in preventing osteocyte apoptosis that also controls osteoclast formation/recruitment and is impaired with aging.

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Disruption of the Cx43/miR21 pathway leads to osteocyte apoptosis and increased osteoclastogenesis with aging

et al. 2017

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“…Animal experiments have shown relations to superoxide and oxidative stress 79 . Six genes with known links to oxidative stress and NO, within these 38 loci were identified (REST 48 , GJA1 49 , YAP1 50 , PRDM16 51 , LRP1 52 , and MRVI1 53 ). This is in line with previous findings 16 , however, in the DEPICT pathway analysis we found that NO-related reconstituted gene sets were not significantly associated with migraine (FDR > 0.54) (Supplementary Table 15).…”

Section: Discussionmentioning

confidence: 99%

“…Six of the loci harbor genes that are involved in nitric oxide signaling and oxidative stress (REST 48 , GJA1 49 , YAP1 50 , PRDM16 51 , LRP1 52 , and MRVI1 53 ).…”

Section: Supplementary Table 6)mentioning

confidence: 99%

Meta-analysis of 375,000 individuals identifies 38 susceptibility loci for migraine

Gormley

Anttila

Winsvold

et al. 2015

Preprint

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Migraine is a debilitating neurological disorder affecting around 1 in 7 people worldwide, but its molecular mechanisms remain poorly understood. Some debate exists over whether migraine is a disease of vascular dysfunction, or a result of neuronal dysfunction with secondary vascular changes. Genome-wide association (GWA) studies have thus far identified 13 independent loci associated with migraine. To identify new susceptibility loci, we performed the largest genetic study of migraine to date, comprising 59,674 cases and 316,078 controls from 22 GWA studies. We identified 45 independent single nucleotide polymorphisms (SNPs) significantly associated with migraine risk (P < 5 x 10-8) that map to 38 distinct genomic loci, including 28 loci not previously reported and the first locus identified on chromosome X. Furthermore, a subset analysis for migraine without aura (MO) identified seven of the same loci as from the full sample, whereas no loci reached genome-wide significance in the migraine with aura (MA) subset. In subsequent computational analyzes, the identified loci showed enrichment for genes expressed in vascular and smooth muscle tissues, consistent with a predominant theory of migraine that highlights vascular etiologies.

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“…Hemichannels are formed by 6 Cx proteins. Cx43 is the major connexin isoform expressed in bone cells and the activity of hemichannels induced by OS is primarily mediated by Cx43 hemichannels (8). Cx43 hemichannels have been shown to regulate the release of NAD + , prostaglandin E2 (PGE2), and ATP in response to mechanical stimulation in osteocytes (8).…”

Section: Introductionmentioning

confidence: 99%

Elevated Intracellular Ca2+ Signals by Oxidative Stress Activate Connexin 43 Hemichannels in Osteocytes

Riquelme

Jiang

2013

Bone Res.

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Elevated oxidative stress (OS) during aging leads to bone loss. OS increases intracellular Ca 2+ ([Ca2+ IntroductionIn oxidation-related cellular damage, an increase in the intracellular Ca 2+ ([Ca 2+ ]i) concentration is known to Osteocytes, comprising of approximately 95% of all bone cells, are embedded inside of the bone matrix. Their long dendritic processes form a communication network between neighboring osteocytes and with cells on the bone surface to regulate bone remodeling. During aging, the number of viable osteocytes decreases gradually (1). Oxidative stress (OS) is thought to be a major factor attributing to osteocyte apoptosis and subsequent bone loss (2). 356the exchange of small molecules (up to ~1 kDa) (7). Hemichannels are formed by 6 Cx proteins. Cx43 is the major connexin isoform expressed in bone cells and the activity of hemichannels induced by OS is primarily mediated by Cx43 hemichannels (8). Cx43 hemichannels have been shown to regulate the release of NAD + , prostaglandin E2 (PGE2), and ATP in response to mechanical stimulation in osteocytes (8). Cx43 plays a critical role in many aspects of bone cell function, including proliferation, survival, and differentiation of osteoblasts, skeletal development, and postnatal bone mass acquisition (9-10). Furthermore, Cx43 is shown to be required for the anti-apoptotic effect of bisphosphonates on osteoblasts and osteocytes in vivo (11). However, the cellular mechanism that regulates the activity of Cx43 hemichannels by OS is poorly understood. In this study, we uncovered the role of intracellular Ca 2+ rise induced by OS in the regulation of Cx43 hemichannels. These findings will ultimately help to illustrate the underlying mechanism of Cx43 hemichannel opening and OSinduced Ca 2+ signals in osteocytic cell death and bone aging. Materials and Methods MaterialsFetal bovine serum (FBS) and calf serum (CS) were from HyClone Laboratories (Logan, UT, USA); rat tail collagen type I, 99% pure, was from Becton Dickinson Laboratories (Bedford, MA, USA); Fluo-4 AM were from Invitrogen (Eugene, OR, USA); EZ-link Sulfo-NHS-LC-Biotin and NeutrAvidine from Pierce Biotechnology (Rockford, IL, USA); paraformaldehyde (16% stock solution) was from Electron Microscopy Science (Fort Washington, PA, USA); nitrocellulose membrane was from Schleicher & Schuell (Keene, NH, USA); Enhanced Chemiluminescence (ECL) kit was from Amersham Biosciences (Piscataway, NJ, USA); X-OMAT AR films were from Eastman Kodak (Rochester, NY, USA). All other chemicals were from either Sigma (St. Louis, MO, USA) or Fisher Scientific (Pittsburgh, PA, USA).Cell culture MLO-Y4 cells were cultured on collagen-coated (rat tail collagen type I; 0.15 mg·mL -1 ) surfaces. Cells were grown in α-modified essential medium (MEM) supplemented with 2.5% FBS and 2.5% CS, and incubated in a 5% CO2 incubator at 37 ℃ as described previously (12). [Ca 2+ ]i changes were monitored in MLO-Y4 cells plated on collagen coated glass bottom cell culture plate (MatTek, Ashland, MA, USA). Cells were ester-loaded wi...

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Connexin 43 Channels Protect Osteocytes Against Oxidative Stress–Induced Cell Death

Cited by 77 publications

References 39 publications

Disruption of the Cx43/miR21 pathway leads to osteocyte apoptosis and increased osteoclastogenesis with aging

Disruption of the Cx43/miR21 pathway leads to osteocyte apoptosis and increased osteoclastogenesis with aging

Meta-analysis of 375,000 individuals identifies 38 susceptibility loci for migraine

Elevated Intracellular Ca2+ Signals by Oxidative Stress Activate Connexin 43 Hemichannels in Osteocytes

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