Osteoblast response against Mycobacterium tuberculosis infection

Kaur Khushpreet *, Karakousis Petros C.^#, Verma Indu*

* Dept. of Biochemistry, Postgraduate Institute of Medical Education and Research, Chandigarh-160012

# Center for Tuberculosis Research, Johns Hopkins University school of Medicine, Baltimore, MD 21287

Tuberculous osteomyelitis is widely characterized by bone loss and bone destruction caused by Mycobacterium tuberculosis (M.tb). It is difficult to treat and usually requires longer anti-tubercular treatment due to bone complexity. The pathogenesis of disease has not yet established. Thus, the present study aimed to investigate whether M.tb invades osteoblasts and, further, how it affects the osteogenesis process resulting into bone loss as seen in patients suffering from tuberculous osteomyelitis. The MC3T3 pre-osteoblast-like cells were infected with M.tb H37Rv-lux. Invasion and intracellular multiplication of M.tb H37Rv-lux was measured in terms of relative luminescence units (RLU). Osteoblast proliferation and differentiation markers were studied at 3,7,14 and 21day post-infection using various osteogenesis markers, such as osteoblast cell proliferation, ALP activity via pNPP substrate solution, collagen deposition using sirius red and calcium mineralization using alizarin red staining. M.tb was found not only to invade, but also to multiply within osteoblasts upto 21days post-infection. Further, significant inhibition of the expression of key markers of osteoblasts growth and division, such as alkaline phosphatase, collagen and calcium mineralization highlighted the effect of M.tb infection in disrupting bone homeostasis, resulting to bone loss. These results suggests that osteoblasts provide a suitable micro-environment for the growth and survival of M.tb. Invasion and multiplication of intracellular bacteria appears to be associated with reduced activity of osteoblast through various coordinated signals, likely accounting for the bone loss observed in cases of tuberculous osteomyelitis. An improved understanding of the mechanisms underlying M.tb-induced bone destruction may yield novel strategies for the treatment of tuberculous osteomyelitis.