The mitochondrial protease, LonP1, is a potential cardioprotective target for attenuating doxorubicin-induced cardiomyocyte death

BACKGROUND: Doxorubicin (DOX), a first-line chemotherapeutic agent, has been linked to severe off-target cardiotoxicity in the clinic. Previous works suggest that mitochondria are key mediators of this cardiotoxicity. Leakage of mitochondrial contents after DOX treatment, including mitochondrial DNA (mtDNA), is thought to activate apoptotic and inflammatory signaling pathways implicated in cardiomyocyte cell death. Whether the master mitochondrial protease, LonP1, can dampen these pathways and improve cardiomyocyte viability following DOX treatment remains unknown. METHODS: Human cardiac cells (AC-16) and primary (1°) human cardiomyocytes were subjected to DOX treatment, followed by bulk RNA-Seq, RT-qPCR, qPCR, and immunoblotting to assess apoptotic signaling, inflammatory signaling, mtDNA release, and LonP1 expression, respectively. Lentivirus transduction of AC-16 cells was used to generate both knockdown (KD) and overexpression (OE) LonP1 cell lines to determine the effects of altered LonP1 levels on DOX-induced apoptosis and mtDNA release. Further, levels of mitochondrial DNA (mtDNA) were measured using qPCR from serum samples obtained from patients undergoing DOX treatment to assess the clinical relevance of released mtDNA as a potential biomarker for the development of DOX cardiotoxicity. RESULTS: DOX treatment of AC-16 cells, as well as 1° human cardiomyocytes, upregulated both apoptotic and inflammatory signaling in both cell models. Increased LonP1 levels were also observed under DOX treatment in AC-16 cells and 1° human cardiomyocytes. Likewise, DOX increased mtDNA release from both cell lines, both prior to, and as a sequel to cell death. Decreasing LonP1 levels exacerbated DOX-mediated apoptotic signaling and mtDNA release, whereas overexpression of LonP1 attenuated these effects. Furthermore, DOX treatment in cancer patients increases plasma mtDNA levels. CONCLUSIONS: These findings suggest LonP1 plays a protective role in the heart following DOX treatment, supporting LonP1 as a potential novel therapeutic target for prevention of DOX cardiotoxicity. Patterns of mtDNA release within patients undergoing DOX treatment also highlight the potential of mtDNA as a potential biomarker and target for prevention of DOX cardiotoxicity, justifying the need for more extensive, prospectively monitored cohort studies to expand upon these findings and statistically model mtDNA release patterns.