Research articles

Targeting mesenchymal stem cells (MSCs), progenitors of osteoblasts, to bone has been a long-standing goal but has had limited success so far. Here, Min Guan and her colleagues deliver a peptidomimetic integrin ligand against integrin α4β1 conjugated to the bone-seeking agent bisphosphonate alendronate as a means of attracting infused and/or endogenous MSCs to the bone surface to stimulate bone formation. The approach was tested in both xenotransplantation and immunocompetent mice, as well as in mouse models of trabecular bone loss induced by aging and estrogen deficiency (ovariectomy).

BMP7 has been previously shown to protect against renal fibrosis. Raghu Kalluri and his colleagues have now identified activin-like kinase 3 (Alk3) as the key co-receptor for BMP7 in the kidney and have identified an orally available, small-peptide agonist of Alk3 that reduces established fibrosis in five animal models of kidney injury.

Tau aggregation is associated with neurodegenerative diseases called tauopathies. Ashley Bush and colleagues now report that aged tau-deficient mice develop motor and cognitive dysfunction that is linked to elevated iron levels in the brains of the mice.

Zhang and colleagues have developed a new targeted delivery system for RNA interference–based bone anabolic therapy. Using dioleoyl trimethylammonium propane (DOTAP)-based cationic liposomes attached to six repetitive sequences of aspartate, serine, serine (AspSerSer)₆, the system provided selective enrichment of the encapsulated osteogenic siRNA in osteogenic lineage cells at the bone formation surface and the subsequent depletion of the target gene, encoding the bone formation inhibitor casein kinase-2 interacting protein-1 (PLEKHO1, also known as CKIP-1), leading to the promotion of bone formation in healthy and osteoporotic rats.

The role of T cells in modulating the course of influenza infection in humans is not clear. Wilkinson et al. now report that, in the absence of strain-specific humoral immunity, preexisting cytotoxic CD4⁺ T cells limit the severity and duration of symptoms in humans challenged with influenza virus and suggest these CD4⁺ T cell responses might be harnessed in vaccine development.

The ability of Mycobacterium leprae to upregulate miRNA-21 provides an effective mechanism for the pathogen to escape from the vitamin D–dependent antimicrobial pathway.

Mutations in isocitrate dehydrogenases 1 and 2 (IDH1 and IDH2) in the majority of people with grade 2 and 3 gliomas is associated with elevated levels of 2-hydroxyglutarate (2HG) within the tumor. As harboring IDH1 or IDH2 mutations confers a considerable survival benefit in these individuals, there has been considerable interest in studying this metabolite as a potential biomarker. Here, Changho Choi et al. report the successful noninvasive detection of 2HG in 30 subjects with gliomas using a proton magnetic resonance spectroscopy approach.

This report uncovers a direct link between cancer-driving inflammation and DNA methylation by showing that PGE₂ regulates the expression of DNA methylases, resulting in silencing of tumor-suppressor genes. The authors suggest that DNA methylation is an important component of the pathogenic effect of inflammatory signaling in colorectal cancer.

By modeling acquired resistance to the EGFR antibody cetuximab in metastatic colorectal cancer, the authors identify a new mutation in the ectodomain of the receptor. The mutation is present in patient tumors after cetuximab therapy, confirming that it represents a clinically-relevant mechanism for therapy resistance. Moreover, the mutation does not affect the response to other EGFR antibodies, suggesting that if independently confirmed it may be a useful indicator to tailor anti-EGFR therapy.

Kejia Cai et al. describe a method to non-invasively detect glutamate (Glu) concentrations in the brain with MRI at high resolution. The approach is based on the pH-dependent chemical exchange saturation transfer (CEST) effect between the amino group of Glu and bulk water and offers advantages over proton magnetic resonance spectroscopy. Feasibility of GluCEST was demonstrated in rat brain after middle cerebral artery occlusion stroke and in a rat brain tumor model, as well as in healthy human brain at 7 Tesla.

Noise-induced hearing loss (NIHL) is a prevalent problem in the industrialized world. Now, Lukas Rüttiger and colleagues show that the phosphodiesterase inhibitor vardenafil can prevent NIHL in rats and mice.

Using mice with an amino substitution in the kinase PKG, a key regulator of blood vessel tone, Oleksandra Prysyazhna et al. provide evidence for the physiological importance of PKG oxidation and disulfide formation in maintaining normal blood pressure. These results clarify the nature of an enigmatic vasodilatory activity termed endothelium-derived hyperpolarizing factor and suggest that vascular oxidative stress can have blood pressure-lowering effects.

Protective T helper 2 (T_H2)-type responses are induced by parasite infection and can control inflammation and induce parasite expulsion. In this issue, Chen et al. report that in a mouse model of helminth infection, T_H2-type responses protect against acute lung tissue damage by both suppressing inflammation and promoting macrophage-associated wound healing.

Cidea is typically thought of as a lipid droplet–associated cytoplasmic protein in brown adipose tissue. Peng Li and colleagues now show that it is also in the nucleus, and in mammary gland epithelial cells it acts as an essential transcriptional coactivator of C/EBPβ to regulate the expression of genes involved in milk lipid secretion during lactation.

Cell-surface glycans are known to alter as Barrett's esophagus progresses to adenocarcinoma, leading to specific changes in lectin binding patterns. Bird-Lieberman and her colleagues have exploited this knowledge to develop a new endoscopic approach that uses fluorescent-labeled lectins to visualize pre-cancerous, high-grade dysplastic lesions in Barrett's esophagus that cannot be detected by conventional endoscopy. The method uses commonly available endoscopic equipment, provides a wide field of view and is shown here in ex vivo esophageal tissue.

The authors identify a new tumor suppressor role for Smurf2 that is linked to its regulation of histone modifications through RNF20. In the absence of Smurf2 in mice, and potentially also when its nuclear function is compromised in human tumors, higher levels of histone ubiquitination lead to a relaxation of chromatin structure, and alterations in DNA repair result in compromised genomic instability and increased tumorigenesis in aging mice. The findings suggest that loss of Smurf2 function may underlie tumor initiation by reshaping the epigenetic landscape of cells.

Mutations in the type I ryanodine receptor (RYR1), a calcium channel, leads to stimulus-induced pathological muscle contractions, including malignant hyperthermia. Currently there are no pharmacological agents to protect against this condition, but Susan Hamilton and her colleagues have now identified AICAR as one possible candidate compound. To date, AICAR has been thought to be an AMPK activator, but her group shows that in a mouse model of malignant hyperthermia it does not target this kinase, but rather RYR1, to prevent improper calcium leakage and pathology.

The Niemann-Pick C1–like 1 cholesterol uptake receptor is an entry factor for the hepatitis C virus, according to this report. Ezetimibe, a drug that targets this receptor and is approved for use in humans, inhibits infection by the hepatitis C virus in a mouse model, highlighting the therapeutic potential of this discovery.