Transgenic cardiac targeted overexpression of human thymidylate kinase (TMPK)

Thymidylate kinase (TMPK) is a nucleoside monophosphate kinase that catalyzes phosphorylation of thymidine monophosphate (TMP) to thymidine diphosphate (TDP). TMPK also mediates phosphorylation of monophosphates of thymidine nucleoside analog (NA) prodrugs on the pathway to their active triphosphate antiviral or anti-tumor moieties. Novel transgenic mice (TG) expressing human (h) TMPK were genetically engineered using the α-myosin heavy chain promoter to drive its cardiac-targeted over-expression. In “2 by 2” protocols, TMPK TGs and wild type (WT) littermates were treated with the NA zidovudine (a deoxythymidine analog, AZT) or vehicle for 35 days. Alternatively, TGs and WTs were treated with a deoxycytidine NA (racivir, RCV) or vehicle. Changes in mitochondrial DNA (mtDNA) abundance and mitochondrial ultrastructure were defined quantitatively by real-time PCR and transmission electron microscopy, respectively. Cardiac performance was determined echocardiographically. Results showed TMPK TGs treated with either AZT or RCV exhibited decreased cardiac mtDNA abundance. Cardiac ultrastructural changes were seen only with AZT. AZT-treated TGs exhibited increased left ventricle (LV) mass. In contrast, LV mass in RCV treated TGs and WTs remained unchanged. In all cohorts, LV end-diastolic dimension (LVEDD) remained unchanged. This novel cardiac-targeted overexpression of hTMPK helps define the role of TMPK in mitochondrial toxicity of antiretrovirals.