Date Published: January 30, 2017
Publisher: Public Library of Science
Author(s): Timothy Casselli, Humaira Qureshi, Elizabeth Peterson, Danielle Perley, Emily Blake, Bradley Jokinen, Ata Abbas, Sergei Nechaev, John A. Watt, Archana Dhasarathy, Catherine A. Brissette, Utpal Pal.
Lyme disease is caused by infection with the bacterium Borrelia burgdorferi (Bb), which is transmitted to humans by deer ticks. The infection manifests usually as a rash and minor systemic symptoms; however, the bacteria can spread to other tissues, causing joint pain, carditis, and neurological symptoms. Lyme neuroborreliosis presents itself in several ways, such as Bell’s palsy, meningitis, and encephalitis. The molecular basis for neuroborreliosis is poorly understood. Analysis of the changes in the expression levels of messenger RNAs and non-coding RNAs, including microRNAs, following Bb infection could therefore provide vital information on the pathogenesis and clinical symptoms of neuroborreliosis. To this end, we used cultured primary human astrocytes, key responders to CNS infection and important components of the blood-brain barrier, as a model system to study RNA and microRNA changes in the CNS caused by Bb. Using whole transcriptome RNA-seq, we found significant changes in 38 microRNAs and 275 mRNAs at 24 and 48 hours following Bb infection. Several of the RNA changes affect pathways involved in immune response, development, chromatin assembly (including histones) and cell adhesion. Further, several of the microRNA predicted target mRNAs were also differentially regulated. Overall, our results indicate that exposure to Bb causes significant changes to the transcriptome and microRNA profile of astrocytes, which has implications in the pathogenesis, and hence potential treatment strategies to combat this disease.
Lyme disease (or Lyme borreliosis) is prevalent across the entire northern hemisphere, including Europe and parts of Asia . In the United States, the Lyme disease spirochete, Borrelia burgdorferi (Bb), is the cause of more than 90% of all arthropod-borne diseases affecting humans . Roughly 30,000 cases are reported to the Centers for Disease Control and Prevention (CDC) every year, but the infection is likely underreported, and revised estimates suggest the rate is closer to 300,000 people affected by Lyme disease per year [1, 3, 4]. Total direct medical costs of Lyme disease and the controversial Post-Treatment Lyme Disease Syndrome (PTLDS) in the USA are estimated at $700 million- $1.3 billion per year .
Transcriptome studies can provide valuable insights into the pathophysiological mechanisms of disease. To date, few studies have examined global differential gene expression induced by Bb in any cell type. In this work, we demonstrate for the first time an extensive dataset of the transcriptional changes, including mRNAs, long non-coding RNAs, and microRNAs, induced by Bb in primary human astrocytes. 275 genes were differentially regulated in astrocytes co-cultured with Bb. Consistent with previous reports on Bb-induced gene expression, we observed alterations in expression of immune response genes including the chemokine genes cxcl1, cxcl6, and cxcl8, as well as il1β [16, 28, 31–33]. Other genes involved in inflammation and infection control that have not previously been linked to Bb infection were observed as well, most notably tumor necrosis factor superfamily member tnfsf18 and chi3l1. TNFSF18 (GITRL) modulates T lymphocyte survival, and both TNFSF18 and its cognate receptor have been implicated in a number of inflammatory and autoimmune diseases in both human patients and experimental models of systemic lupus erythematosus, autoimmune encephalomyelitis, arthritis, and autoimmune diabetes [43–46].
We identified 275 RNAs and 38 microRNAs differentially expressed in human astrocytes in response to the Lyme disease spirochete, Bb. The identified genes include both previously characterized and novel gene expression changes associated with Bb infection. The expression changes of these RNAs and microRNAs could in part provide an explanation for the persistence of Lyme disease symptoms. Understanding how these changes are maintained over time will be of great importance in developing effective treatments to Lyme disease.