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In mid-March, we were told to stay home—for a couple of weeks. Four months later, we are still, for the most part, staying home, slowly adapting to a new normal. By physically isolating us, the COVID-19 pandemic has forced us to adapt—we became teachers, caregivers, chefs, and personal trainers. It also forced us to change how we communicate with each other. We have been using video chats relentlessly—for job interviews, professional meetings, Friday happy hours, birthday anniversaries, and playdates. And while we certainly miss meeting each other in person, we have learned to listen and communicate better.
As humans, we communicate with our family members, neighbors, and friends and colleagues worldwide, with each of these requiring specialized and unique tools and styles. Similarly, cells communicate with cells near and far to proliferate, differentiate, migrate, and survive. Cells communicate with their direct neighbors to establish and maintain the morphogenesis of developing tissues. They can also communicate with distal cells to specify cell fate. Organelles within a single cell and molecules within these cellular compartments also communicate with each other. And just as we use words, signs, facial expressions, and eye contacts to communicate with each other, cells also use a variety of means to communicate. One such communication tool, and one that can be adapted to intracellular signaling all the way to signaling throughout the body, is metabolic signals.
Metabolic signals can arise from both anabolic and catabolic processes. During development, when food is plentiful, anabolic signals instruct cells to proliferate, tissues to build, organs to grow. By contrast, when energetic resources are sparse, catabolic signals break down large molecules into smaller ones to release energy. Organelles, cells, tissues, or whole organisms sense and transmit these metabolic signals to ultimately control systemic energy homeostasis. When these processes go awry, diseases such as cancer arise. In this special issue, we are featuring pieces that discuss the recent progress made in understanding how metabolic signals regulate cellular communication in the context of cellular homeostasis, development, and diseases. These Reviews and Perspectives also illustrate that metabolic communications occur at multiple scales. At the cellular level, metabolic signals can converge on one organelle to regulate its function. They can also orchestrate the function of distinct organelles by modulating their physical contact sites. By maintaining the energy homeostasis of specific tissues, metabolic signals also contribute to organ growth and function. They are essential during development, where they control cell growth and cell fate by regulating cell signaling pathways or chromatin state. While controlling systemic energy homeostasis, metabolic signals also contribute to aging and cancer, and it is now known that manipulating these pathways can have beneficial effects. Together, these Reviews and Perspectives underline how metabolic signals influence all aspects of life—they contribute to cell growth and cell fate, maintain tissue homeostasis and organ function, promote cancer proliferation and invasion, regulate lifespan. And the field is wide open to further understanding the nature of these metabolic signals, their regulation, how they are sensed and transmitted, and how they integrate with each other in a whole organism throughout its development and lifetime.
We would like to end by thanking our authors and reviewers. This special issue would not have been possible without all of the authors who contributed to it. Their submission deadline came just when stay-at-home orders were first issued, forcing them to close their labs and to conduct their lectures and mentor students virtually, while adapting to life at home with family and kids. Our reviewers, although behind the scenes, also significantly contributed to improving all these pieces by providing constructive and thorough feedback in a timely manner in very unusual times. We hope that you will enjoy this special issue and that it will inspire you to start new research projects. We are looking forward to reading the papers that will result from it.