OPA1-driven cristae remodeling promotes pancreatic cancer progression

Mitochondria are dynamic organelles that participate in various cellular processes such as bioenergetic homeostasis, signaling cascades and redox state control, ultimately influencing cell fate decisions. The diversity of mitochondrial functions resonates in the dynamic nature of their morphology. Indeed, both mitochondrial ultrastructure and network organization influence mitochondrial function and are both highly dynamic to respond to cellular demands quickly. As signaling organelles, mitochondria communicate with other cellular compartments through several mechanisms, including the release of metabolites, ROS production, and changes in their localization and shape. These alterations occur in response to environmental cues making mitochondria essential cellular stress sensors. In cancer, where low nutrient and oxygen levels often characterize local microenvironments, mitochondria play a central role in adaptation to stress, facilitating cancer cell proliferation in harsh conditions. This is well exemplified in pancreatic ductal adenocarcinoma (PDAC), which is one of the deadliest cancers worldwide and is characterized by a prominent desmoplastic reaction and a near avascular microenvironment that hampers nutrient/oxygen supply. Notably, over the last years, a compelling body of work has shown that metabolism is profoundly altered in PDAC. My thesis aims to dissect the significance of the rewiring of mitochondrial function and morphology during PDAC progression to identify potential targetable mechanisms driving tumor aggressiveness. Quantitative analysis of the mitochondrial proteome in cellular models of stepwise pancreatic carcinogenesis revealed increased levels of proteins involved in metabolic pathways, protein import, and mitochondrial translation. These alterations included unexpected upregulation of components of the oxidative phosphorylation pathway, validated by the increase in mitochondrial respiration in late-stage PDAC cells. Changes in mitochondrial respiration correlated with modifications in mitochondrial ultrastructure both in vitro and in vivo. Further investigation identified members of the NDPK family, including NME4, as drivers of these changes in mitochondrial ultrastructure. Indeed, NME4 has been associated with the regulation of the GTPase activity of OPA1, the master regulator of cristae stability. NME4, in a complex with OPA1, has a crucial role in the regulation of mitochondrial ultrastructure, as its silencing in HeLa cells disrupts mitochondrial cristae. Accordingly, NME4 loss reshapes mitochondrial ultrastructure and impairs mitochondrial respiration in pancreatic cancer cells. High protein levels of either NME4 or OPA1 are associated with poorer survival outcomes, highlighting their clinical relevance. These data highlight the crucial role of mitochondrial ultrastructure in promoting pancreatic carcinogenesis, but mechanisms remained elusive. We leveraged both functional genomics to manipulate Opa1 expression and autochthonous mouse models of pancreatic carcinogenesis. Our results demonstrated that OPA1 elevation promotes active DNA duplication, histone hyper-acetylation, and cellular proliferation both in vitro and in vivo. These phenotypes have all been linked to PDAC development. Accordingly, OPA1 overexpression accelerates PDAC progression in vivo, while targeting OPA1 hinders pancreatic cancer cell growth, without affecting non-transformed pancreatic ductal cells. In summary, this research significantly advances our understanding of mitochondrial reshaping during pancreatic carcinogenesis, revealing the intricate interplay between mitochondrial dynamics, cell cycle regulation, and tumor progression. Key players like NME4 and OPA1 can be envisaged as exciting therapeutic targets. Nonetheless, future research could delve deeper into the molecular intricacies of NME4 and OPA1 function and explore in more detail the molecular mechanisms beyond their role in pancreatic tumorigenesis.