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Osteoporosis: immune system disorders also play an important role

(Vienna, 16-10-2015) In Austria, around 740,000 people are affected by osteoporosis, 600,000 of whom are women. Alongside the "classic" factors involved in the development of this disease – such as oestrogen deficiency, genetic predisposition, hormonal changes and smoking – immune system disorders play a more significant role than was thought some years ago. This aspect is being researched in the field of so-called osteoimmunology by a working group led by Peter Pietschmann (Institute of Pathophysiology and Allergy Research) at MedUni Vienna. The aim is to be able to suppress these inflammatory responses in the future and in this way slow down the disease. 

Osteoporosis is the result of disparity between the rate of bone loss and that of bone formation. This leads to changes in bone mass and the microarchitecture of osseous tissue.  The result is a decline in bone strength and therefore an increased risk of fractures. "More than 50% of this multifactorial disease is down to genetics," says Pietschmann. The other risk factors for developing osteoporosis include hormonal changes, environmental factors, calcium or vitamin D deficiency and smoking.

The interaction between the immune system and osteoporosis plays a greater role than previously thought. It is known that numerous inflammatory diseases such as rheumatoid arthritis, systemic lupus or Crohn's disease, for example, are associated with an elevated long-term osteoporosis risk. However, even mechanisms that are independent of classic inflammations result in excessive osteoclast activity and therefore to bone loss.

It is the so-called pro-inflammatory cytokines, which activate the osteoclasts that attack bone and at the same time retard bone-building osteoblasts, that are responsible for this. "If we are able to specify and block these cytokines and other molecules that are involved, we will be better able to combat osteoporosis," explains Pietschmann on the occasion of today's 14th Viennese Osteoporosis Day (Vienna Town Hall, 10 a.m. – 6 p.m.) and the upcoming World Osteoporosis Day on 20 October. In older people there is often increased production of cytokines and other inflammatory triggers; known as “inflammaging" in medical jargon. This term was coined by the Italian gerontologist Claudio Francheschi.

The aim is to develop new therapeutic approaches that interfere directly in bone metabolism and halt the destruction of bone at an early stage. A therapeutic approach using a RANK ligand (RANKL) antibody is already available. RANKL (Receptor Activator of Nuclear factor Kappa B Ligand) is a substance that is formed by a subgroup of white blood corpuscles, the T-cells, amongst others. This immune system messenger substance promotes the formation of osteoclasts, the cells that break down bone.

Research in the Immunology Cluster at MedUni Vienna
Pietschmann’s working group is established within the Immunology Research Cluster (Director: Wilfried Ellmeier) – one of five research clusters at MedUni Vienna – thereby facilitating interdisciplinary research and maximizing resources. "With our micro-computed tomography devices we have optimum technical resources, even when compared internationally, and that is a major factor in our research successes," says the MedUni Vienna researcher. In a current ongoing study, the Viennese researchers were also able to show that oxidative stress plays a role in the development of osteoporosis. And incidentally, it was Pietschmann himself who coined the term "osteoimmunology" in 1997.