Additionally in a previous transgenic

Additionally, in a previous transgenic model with autotaxin under the control of the MMTV-LTR promoter, aberrant expression of human autotaxin caused late-onset, metastatic breast cancer [5]. The AT-ATX transgenic model is analogous to the previous one because ∼30% of all spontaneous tumors appeared in the mammary glands of mice. Overall, approximately 21% of transgenic animals developed tumors. Although this is a smaller percentage than we predicted, it is comparable to the percentage of patients presenting with HER2-positive breast cancer, which tends to be more aggressive than ER-positive disease. It also correlates with the data we retrieved from The Cancer Genome Atlas showing that ∼19% of invasive breast cancers have an autotaxin alteration [14,15]. Autotaxin has a well-known role in mediating tumorigenesis [33,34]. The autotaxin-mediated miRNome signature derived from our model shows upregulation of miR-34c-5p, miR-34b-5p, and miR-30c-2-3p. The former two miRNAs have been found to play protective roles for cancer Balaglitazone in lung cancer and thyroid carcinoma, respectively. This lends importance to their overexpression in the presence of elevated autotaxin as a precursor to tumorigenesis here [35,36]. Limitations of this study arose while delineating the miRNA signature and conducting homology verification to segregate clinically relevant human miRNAs. Among the 126 miRNAs verified, several miRNAs showed significant and interesting trends, but did not have strong homology to corresponding human miRNA. For example, miR-2137 had a similar sequential increase in expression similar to miR-489-3p, however, it is not present in humans and therefore clinically irrelevant. Other miRNAs did not appear in the DIANA TarBase database as having any potential targets based on sequence alignment. Thus, we can interpret the known components appearing in our serum miRNome, but are technically limited and unable to interpret 100% of the information, due to currently nonexistent scientific knowledge.
Conflict of interest statement
Acknowledgements The research was supported by a grant from the National Institutes of Health1R15CA176653 (to MMM). We would like to thank Dr. Aaron M. Beedle for assistance with the transgenic animals.
Introduction Although non-steroidal anti-inflammatory drugs (NSAIDs) and cyclooxygenase-2 (COX-2) inhibitors are the most commonly used medications for osteoarthritis (OA) pain, their side effect concerns and lack of satisfactory pain relief in a large proportion of patients suggest the need for drugs that target other pain mechanisms1, 2. Inhibition of autotaxin represents a potential novel mechanism for treating OA pain. Autotaxin is an extracellular enzyme with lysophospholipase D activity whose primary substrate is the lipid lysophosphatidyl choline (LPC). Autotaxin cleaves choline from LPC to generate lysophosphatidic acid (LPA), a bioactive lipid mediator that signals through the activation of six G-protein coupled receptors (GPCRs) (LPA Receptors 1–6)3, 4, 5. LPA signaling through its receptors results in the induction of several downstream signaling pathways that result in a variety of effects, including cell proliferation, migration, angiogenesis, increase in cytokine signaling and ion channel activation6, 7, 8. Autotaxin knockout mice have an embryonic lethal phenotype due to defects in blood vessel formation. However, heterozygous mice are viable and show a 50% decrease in autotaxin activity and circulating LPA levels, suggesting that autotaxin is the primary enzyme responsible for the production of LPA in plasma. Autotaxin heterozygous mice show decreased sensitivity to pain evoked via mechanical or thermal stimulation in animals subjected to partial ligation of the sciatic nerve. Intrathecal LPC induced mechanical allodynia (assessed in a paw pressure test) and thermal hyperalgesia (assessed in a thermal paw withdrawal test) are significantly reduced in autotaxin heterozygote animals, suggestive of a decreased conversion of LPC to LPA and direct intrathecal administration of LPA has the ability to induce a chronic pain response in rodents. Cyclic phosphatidic acid (cPA) and its stable analog carbacyclic phosphatidic acid (ccPA) are inhibitors of autotaxin, and they have been shown to inhibit acute and chronic pain in animal models. A small molecule inhibitor of autotaxin has been shown to inhibit the local production of LPA and inhibit the vocalization response, a surrogate measure of inflammatory pain in the rat adjuvant induced arthritis model. Mice that lack some of the LPA receptors (LPA1, LPA3 and LPA5) have also been demonstrated to be resistant to neuropathic pain after peripheral nerve injury12, 15, 16. These data provide evidence for a role for autotaxin and LPA in inflammatory and neuropathic pain.