Douglas Millay , PhD

My research interests include skeletal muscle development and regeneration, cell-cell fusion, exercise-induced muscle adaptations, aging and muscular dystrophy. In my lab, we strive to find answers to these questions:

• How do muscle stem cells fuse to generate an adult muscle cell that contains multiple nuclei?
• What needs to happen to muscle cell membranes to drive membrane fusion and muscle formation?
• What is the purpose of muscle stem cell fusion during exercise and aging?
• How do the hundreds of nuclei in a muscle cell regulate transcription?
• Can novel therapeutic delivery vehicles be designed for skeletal muscle?

We have launched a scientific program to identify the factors that regulate cell-cell fusion, delineate their biochemical functions and biophysical properties associated with membrane coalescence, and ultimately translate that information to augment pathological conditions. To accomplish these goals, my lab has initiated multiple lines of investigation using skeletal muscle as a model system to study fusion.

Skeletal muscle is a unique tissue composed of individual cells (myofibers) that contain hundreds of nuclei that form from the fusion of precursor cells during development. Interrogation of this developmental process allows us to identify factors regulating fusion and probe their mechanism of action. Additionally, skeletal muscle is a very plastic tissue in an adult with the ability to regenerate due to the presence of bona fide stem cells. It also responds to various stimuli by altering its contractile and metabolic properties.

Dysregulated maintenance of skeletal muscle can have significant deleterious consequences, including muscular dystrophy (genetic muscle disease), exercise intolerance (not able to obtain the systemic benefits of exercise), the sequelae of metabolic syndrome (obesity, diabetes and cardiovascular dysfunction) and the loss of muscle mass during aging (sarcopenia). Proper regulation of skeletal muscle involves adaptations in the myofiber by the hundreds of existing myonuclei and the fusion of muscle stem cells to generate new myonuclei. Thus, skeletal muscle represents an ideal model system to decipher mechanisms of cellular fusion and understand the control of adaptability in a multinucleated cell.

The detailed mechanisms underlying plasma membrane fusion is an area of mammalian cell biology that is nearly undefined despite its importance in development and physiology. The main reason for this deficiency is proteins that function directly in the fusion of plasma membranes have not been identified, except for our discovery of myomaker during my post-doctoral training. In my independent lab, we identified a second myogenic fusion protein (myomerger) that, together with myomaker, can induce fusion of normally non-fusing cells. This discovery is the first time that cell fusion has been reconstituted with mammalian proteins.

Next, we discovered that the myomaker/myomerger system drives fusion through a novel mechanism, unlike traditional membrane fusion proteins (such as SNAREs). Instead, they independently govern distinct points of the fusion pathway. Muscle stem cell fusion has a well-recognized role during regeneration. However, there is currently no consensus in the field as to whether fusion is required for adult muscle growth, homeostasis and aging. Using our unique myomaker targeted alleles, we have shown that muscle stem cells are necessary for overload-induced muscle growth in adults.

We then developed a novel exercise protocol and showed that muscle undergoes various adaptations to exercise, each having a different requirement for muscle stem cell fusion. Collectively, these findings lead to the novel paradigm that newly added myonuclei are distinct from existing myonuclei. Using single nuclear RNA-sequencing, we are discovering transcriptional dynamics for muscle nuclei, which has the potential to be harnessed to augment aging-induced muscle loss.

I began my work at Cincinnati Children’s in 2014 and have been a researcher for more than 17 years. I am a recipient of the Pew Scholar Biomedical Sciences award in 2015 and the Cincinnati Children’s Endowed Scholar award in 2019. Our lab supports an exciting and dynamic field of study, and we are always looking for hard-working and curious scientists to work on our team!