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Protein appears to protect against bone loss in arthritis.

A small protein named GILZ appears to protect against the bone loss that often accompanies arthritis and its treatment, researchers from the Georgia Regents University report.

Arthritis as well as aging prompt the body to make more fat than bone, and the researchers have previously shown GILZ can restore a more youthful, healthy mix. It also tamps down inflammation, a major factor in arthritis.  Now researchers have early evidence that GILZ might one day be a better treatment option for arthritis patients than widely used synthetic glucocorticoids, which actually increase bone loss.  The current study was presented at The American Society for Bone and Mineral Research Annual Meeting.

In addition to bone loss, glucocorticoids, such as prednisone, produce other side effects, including diabetes. While GILZ is induced by glucocorticoids, directly overexpressing the protein appears to better target sources of bone loss and inflammation and avoid these serious side effects. .

For this study, the focus was tumour necrosis factor alpha, a proinflammatory cytokine that helps regulate immune cells and is a major player in arthritis. Tumour necrosis factor alpha primarily works though promoting inflammation, which is great if the target is cancer. However, when tumour necrosis factor alpha becomes dysregulated, it can also cause diseases like arthritis and inflammatory bowel disease.

To look specifically at the impact on bone loss, the researchers crossed mice bred to overexpress tumour necrosis factor alpha throughout the body with mice that overexpressed GILZ in just their mesenchymal stem cells. These stem cells produce the osteoblasts, which make bone. They also make fat, and when the cells stop making as much bone, they tend to make more of it. The lab has shown that GILZ can coax mesenchymal stem cells back to making more bone and less fat.

While the mice that overexpressed only tumour necrosis factor alpha quickly developed arthritis along with significant bone and weight loss, those that also overexpressed GILZ had significantly less bone loss.

Previous studies have shown that the GILZ transgenic mouse can make more bone. In this instance the group wanted to see if GILZ would still have a bone protective effect in an inflammatory environment similar to arthritis.

Next steps include developing an oral medication, a peptide specifically, that increases GILZ expression rather than the genetic alterations the researchers have used in animal models.  The researchers also want to see if GILZ can prevent arthritis from developing in the face of inflammation.

Glucocorticoids and GILZ are both produced naturally in the body. Glucocorticoids are steroid hormones that help regulate the body’s use of the fuel glucose and dampen the immune response.

Source:  Medical College of Georgia at Georgia Regents University

Schematic illustration of the role of GILZ as mediator of both anti-inflammatory and immunosuppressive glucocorticoid activities and aldosterone-induced ENaC-mediated Na+ transport. GILZ, induced by glucocorticoids, directly interacts with NF-κB, inhibits NF-κB-dependent transcription and mediated anti-inflammatory and immunosuppressive effects in lymphoid and myeloid compartment. Shc/Grb2/Sos complex converts Ras into its active GTP-bound form, leading to the activation of ERK-1/2 and Akt/PKB pathways. GILZ binds Ras and Raf in dimeric or trimeric conformation and diminishes the activation of Ras/Raf downstream targets, including ERK-1/2, Akt, Rb phosphorylation, and cyclin D1 expression, leading to inhibition of Ras- and Raf-dependent cell proliferation and Ras-induced transformation. GILZ, induced by aldosterone, inhibits ERK-1/2 phosphorylation, leading to increased expression of surface α subunit of the ENaC and augmentation of ENaC-mediated Na+ current in the kidney. See text for details. MR, mineral corticoid receptor; Al, aldosterone; GR, glucocorticoid receptor; GC, glucocorticoid; ShC, Grb2, adaptor proteins; SOS, GTP-exchange factor. Red T-headed leaders indicate inhibition; green arrow-headed leaders indicate activation.  Riccardi et al 2009.
Schematic illustration of the role of GILZ as mediator of both anti-inflammatory and immunosuppressive glucocorticoid activities and aldosterone-induced ENaC-mediated Na+ transport. GILZ, induced by glucocorticoids, directly interacts with NF-κB, inhibits NF-κB-dependent transcription and mediated anti-inflammatory and immunosuppressive effects in lymphoid and myeloid compartment. Shc/Grb2/Sos complex converts Ras into its active GTP-bound form, leading to the activation of ERK-1/2 and Akt/PKB pathways. GILZ binds Ras and Raf in dimeric or trimeric conformation and diminishes the activation of Ras/Raf downstream targets, including ERK-1/2, Akt, Rb phosphorylation, and cyclin D1 expression, leading to inhibition of Ras- and Raf-dependent cell proliferation and Ras-induced transformation. GILZ, induced by aldosterone, inhibits ERK-1/2 phosphorylation, leading to increased expression of surface α subunit of the ENaC and augmentation of ENaC-mediated Na+ current in the kidney. See text for details. MR, mineral corticoid receptor; Al, aldosterone; GR, glucocorticoid receptor; GC, glucocorticoid; ShC, Grb2, adaptor proteins; SOS, GTP-exchange factor. Red T-headed leaders indicate inhibition; green arrow-headed leaders indicate activation. Riccardi et al 2009.

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