Abstract
MicroRNAs have been proposed as biomarkers for equine sarcoids, the most prevalent equine skin tumors globally. This study served to validate the diagnostic and prognostic potential of whole blood microRNAs identified in a previous study for long-term equine sarcoid diagnosis and outcome prediction. Based on findings of a clinical examination at the age of 3 years and a follow-up following a further 5-12 years, 32 Franches-Montagnes and 45 Swiss Warmblood horses were assigned to four groups: horses with regression (n = 19), progression (n = 9), new occurrences of sarcoid lesions (n = 19) and tumor-free control horses (n = 30). The expression levels for eight microRNAs (eca-miR-127, eca-miR-432, eca-miR-24, eca-miR-125a-5p, eca-miR-134, eca-miR-379, eca-miR-381, eca-miR-382) were analyzed through reverse transcription quantitative polymerase chain reaction in whole blood samples collected on initial examination. Associations of sex, breed, diagnosis, and prognosis with microRNA expression levels were examined using multivariable analysis of variance. Sex and breed influenced the expression level of five and two microRNAs, respectively. Eca-miR-127 allowed discrimination between sarcoid-affected and tumor-free horses. No variation in microRNA expression was found when comparing horses with sarcoid regression and progression. Expression levels of eca-miR-125a-5p and eca-miR-432 varied in male horses that developed sarcoids throughout the study period in comparison to male control horses. While none of the investigated miRNAs was validated for predicting the prognosis of sarcoid regression / progression within young horses with this condition, two miRNAs demonstrated potential to predict if young male (though not female) tumor-free horse can develop sarcoids within the following years. Sex- and breed- biased miRNAs exist within the equine species and have an impact on biomarker discovery.
Highlights
Equine sarcoids (ES) are the most globally prevalent skin tumors in equids [1, 2]
This study aims to replace next-generation sequencing (NGS)(which is essentially an elaborate technique, and is unpractical for routine clinical diagnostics) with reverse transcription quantitative polymerase chain reaction (RT-qPCR), a less expensive and time-consuming miRNA quantification method for validation potential biomarkers in a larger, more diverse and independent study population [30]
Cases were excluded from the study whenever relevant information was missing within clinical records, clinical diagnosis was equivocal, no initial blood sample was available, or whenever the horse was lost to follow-up
Summary
Equine sarcoids (ES) are the most globally prevalent skin tumors in equids [1, 2]. Bovine papillomavirus 1 and 2 (BPV 1 and 2) are considered as the major etiological agents of ES [3]. Genetic susceptibility appears to play an important role and is thought to have a polygenic base [4, 5]. Non-invasive methods comprise polymerase chain reaction (PCR) analyses for BPV 1 and 2 from swabs collected from the surface of putative ES lesions, together with clinical diagnosis (based on typical lesion appearance / localization and has approximately 80% sensitivity and specificity [7,8,9,10]). Adjunct non-invasive tests can improve the reliability of ES diagnosis
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