Distal symmetrical polyneuropathy (DSP) is the most common form of human immunodeficiency virus (HIV) infection-associated peripheral neuropathy and is frequently associated with pain, however it is often under-diagnosed and/or under-treated. Unfortunately, amongst the extensive current HIV/AIDS (acquired immunodeficiency syndrome) research, DSP is an understudied area with few animal models available. It has been previously shown that C57BL/6 mice infected with LP-BM5, a murine retroviral isolate, develop a severe acquired immunodeficiency syndrome similar to humans infected with HIV, hence the term murine AIDS (MAIDS). LP-BM5 infection also induces CNS encephalopathy and cognitive deficits in C57BL/6 mice that are prevented by treatment with the anti-retroviral agent azidothymidine. Our preliminary experiment shows that LP-BM5 induced significant hind limb mechanical hypersensitivity and loss of peripheral nerve fibers in the foot pad skins, signs of peripheral neuropathy, along with the development of MAIDS, suggesting that LP-BM5 infection could be a potential rodent model of HIV/AIDS associated painful peripheral neuropathy. The current proposal is the first attempt to characterize LP-BM5-induced peripheral neuropathy in C57BL/6 mice and investigate the mechanisms in LP-BM5-induced neuropathy. We hypothesize that peripheral LP-BM5 viral infection leads to a painful peripheral neuropathy, presented as hind limb mechanical hypersensitivity and reduced foot pad intraepidermal nerve fiber (IENF) density in susceptible C57BL/6 mice and that spinal cord microglial LP-BM5 infection and its direct or indirect induction of microglial CD40 up- regulation contribute to LP-BM5-induced peripheral neuropathy. The central hypothesis will be tested through three specific aims: 1) Characterize the time course of the development of LP-BM5-induced peripheral neuropathy;2) Identify the specific cellular target of LP-BM5 in the lumbar spinal cord;and 3) Determine the role of spinal cord microglial CD40 in LP-BM5-induced peripheral neuropathy. CD154 (CD40L)-CD40 interaction is known to be critical in the development of the features of MAIDS. Also both CD40 signaling and CNS microglia are critical in the pathogenesis of HIV encephalitis as well as peripheral nerve injury-induced neuropathy. Assessing the role of microglial CD40 will further provide underlying mechanisms involved in the LP-BM5-induced peripheral neuropathy. The long-term goal of the proposed study is to provide further knowledge on retroviral infection-induced neuropathy that could lead to a better understanding of, and more effective treatments for, HIV infection-associated painful peripheral neuropathy.
It is estimated that 33 million people worldwide were living with HIV/acquired immunodeficiency syndrome (AIDS) at the end of 2007 (The 2007 United Nations AIDS epidemic update reports), and as such, greater attention is being focused on the treatment of the numerous HIV infection-related complications. As the most common form of HIV infection-associated peripheral neuropathy, painful distal symmetrical polyneuropathy (DSP) is often under-diagnosed and/or under-treated partially due to a lack of available animal models. The current study carries great potential for establishing a rodent model of HIV infection associated DSP in humans and may lead to more effective treatments.
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