Ross River virus (RRV) is a mosquito-borne alphavirus and the aetiological agent of
epidemic polyarthritis (EPA). Arthropod borne-Alphaviruses that are related to RRV,
such as Chikungunya virus, Sindbis virus and Barmah Forest virus, are usually
associated with epidemics of infectious arthritides in different parts of the world. In
humans, RRV-induced disease symptoms include fever, rash, myalgia and pain and
stiffness of the joints. Muscle and joint pain are the most debilitating symptoms in RRV
patients and the best treatment available is non-steroidal anti-inflammatory drugs
(NSAID). Previous studies in mice have demonstrated that RRV infection results in
inflammation of skeletal muscle and joints and that macrophages play a primary role in
disease.
The present study was carried out to further elucidate the underlying mechanisms
mediating RRV-induced muscle and joint pathology. Previous studies have reported
that encephalitic alphaviruses trigger apoptosis of brain cells in mice and that blocking
apoptosis reduces mortality rates. In the present study, the ability of RRV to induce
muscle apoptosis was investigated in vitro, using a murine myoblast cell line (C1C12),
and in vivo, using a mouse model of RRV disease. RRV-infected C1C12 myofibres
displayed an array of morphological and biochemical makers of apoptosis. Apoptosis
was also observed in the skeletal muscle of RRV-infected C57BL/6J mice. Blocking
apoptosis by general caspase inhibition resulted in milder disease symptoms, reduced
myofibre damage and decreased inflammation of muscle and joint tissues. The total
number of cell infiltrates as well as the number of macrophages infiltrating muscle was
significantly reduced by the treatment with a caspase inhibitor.
The effects of RRV infection on the skeletal system were also investigated. Primary
human osteoblast cells were infected with RRV and monitored for viral-induced
cytopathic effect. Osteoblasts supported rapid virus growth and, by 48 hours after
infection, succumbed to viral-induced necrosis. In addition, histological examination of
bone tissue from RRV-infected C57BL/6J mice showed clear evidence of bone
resorption. Tibias from infected mice showed an increased number of activated
osteoclasts, a reduction in bone density and thinning of cortical bone.
The expression of host factors involved in inflammatory responses and bone
remodelling was studied in RRV-infected myofibres and osteoblast cell cultures and in
the muscle and joint tissues from infected mice. RRV-infected muscle cells and tissue
showed elevated mRNA levels for the chemokines CCL-2, CCL3, CCL5 and CXCL1,
all of which are known to mediate the migration of monocytic cells. With the exception
of CXCL1, these chemokines were also found to be up-regulated in RRV-infected
osteoblast cultures and in joint tissues from infected mice. Muscle and joint tissue from
infected mice also showed elevated mRNA levels for type I and type II interferons,
TNF- and NOS2. In addition, joint tissues from infected animals contained high levels
of IL-6 and IL-1, two cytokines known to mediate bone remodelling.
Finally, the therapeutic potential of the drug bindarit was investigated using the mouse
model of RRV disease. Bindarit is a known inhibitor of CCL-2 and TNF- and has
been found to prevent protein denaturation. Treatment with bindarit resulted in mice
developing milder disease symptoms, reduced muscle damage and decreased
inflammation of muscle and joint tissues. In particular, bindarit significantly reduced
macrophage infiltration into skeletal muscle tissue.
This thesis has contributed to the understanding of RRV pathogenesis. It has identified
novel mechanisms of RRV-induced muscle and bone pathology and provided further
evidence that associate pro-inflammatory host factors to RRV disease. This work has
also demonstrated that bindarit should be considered as a candidate for treating RRV
disease in humans.
| Identifer | oai:union.ndltd.org:ADTP/219590 |
| Date | January 2007 |
| Creators | Rulli, Nestor Ezequiel, na |
| Publisher | University of Canberra. School of Health Sciences |
| Source Sets | Australiasian Digital Theses Program |
| Language | English |
| Detected Language | English |
| Rights | ), Copyright Nestor Ezequiel Rulli |
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