Influence on hepatocellular carcinoma energy metabolism by pharmacological inhibition of the epigenetic modifier LSD1

Question:

Epigenetic alterations play an important role in carcinogenesis. The lysine demethylase 1 (LSD1), regulating transcription by demethylation of histone 3 at lysine 4 and 9, is an epigenetic modifier, which is overexpressed in many cancer types including hepatocellular carcinoma (HCC). Our recent studies have demonstrated that LSD1 inhibition impairs cell growth and invasion. Hereby, we now addressed the question which mechanistic links are affected by LSD1 inhibition using the novel LSD1 inhibitor HCI-2509.

Methods:

Ultra-deep RNA-sequencing of LSD1 inhibited and non-inhibited HCC cells (Huh7, HepG2, Hep3B) was followed by comprehensive pathway analysis (IPA). Divergent expression in response to LSD1 inhibition was then verified by quantitative PCR. Changes of the mitochondrial membrane potential were investigated by confocal microscopy and flow cytometry. Metabolic and respiratory changes were further determined by the Seahorse platform. Besides, TCGA data (National Cancer Institute) from HCC patients were evaluated with respect to differential expression of LSD1 targeted metabolic genes in malignant versus healthy liver samples.

Results:

Gene expression profiling followed by pathway analysis of hepatoma cell types revealed a prominent dysregulation of genes involved in the cell cycle control and mitochondrial function after pharmacological LSD1 inhibition using HCI-2509. Especially, genes encoding subunits of the mitochondrial respiratory complex were repressed. In agreement, the mitochondrial membrane potential was decreased after LSD1 inhibition and metabolic analysis revealed reduced ATP production and a low respiratory capacity. Loss of mitochondrial function is accompanied by reduced expression of enzymes involved in mitochondrial metabolism, but with a pronounced increase of mitophagy sensors' expression. Furthermore, TCGA data from HCC patients pointed to a distinct difference of the expression of LSD1 targeted metabolic genes in tumor samples compared to non-transformed tissues.

Conclusions:

Our findings show that LSD1 inhibition leads to an impaired cellular respiration caused by a strong repression of the electron transport chain complex I and the overexpression of mitophagy inducers. Hence, our data emphasizes the value of pharmaceutical LSD1 inhibition as an antineoplastic therapeutic option, affecting HCC cell proliferation not only by cell cycle interruption, but also by mitochondrial dysfunction and energetic restriction.