BioPhotonics spoke with Irina Larina, professor in the Department of Integrative Physiology at Baylor College of Medicine. She is an SPIE Senior Member and a Fellow of Optica. She spoke to us about her team’s recent experiments using an optical coherence tomography (OCT) technique to understand the behavior of cilia — tiny, hairlike structures — in the female reproductive system and elsewhere in the body. So, you are using time-lapse OCT imaging and fast Fourier transform to capture cilia movement, presumably separating normally functioning cilia with those that are not? We are using time-lapse OCT imaging to distinguish cilia from surrounding tissues and cells by intensity fluctuations in the images. Cilia are too small to discriminate them within OCT structural images based on their morphology, but because motile cilia beat periodically, they produce periodic intensity fluctuations in the corresponding pixels of OCT images. We use the fast Fourier transform [algorithm] to find pixels with periodic intensity fluctuations, which mark locations of motile cilia. The dominant peak of the Fourier spectrum indicates the cilia beat frequency. The innovative component of our recently published study in Optica lies in the investigation of how ciliary dynamics are coordinated among neighboring cilia. This is crucial as cilia work collectively to move cells and mucus, and precise coordination, beyond just beat frequency, is essential for their transport function. The formation of cilia metachronal waves propagating along ciliated surfaces, due to slight delays between individual neighboring cilia, is a key focus. We developed a method that allows one to map not only the frequency but also the phase of cilia fluctuations in space and time, and visualize the propagation of cilia metachronal waves volumetrically through tissue layers. What have been the limitations of other technologies that could have been employed for this purpose? Traditionally, the examination of ciliary dynamics is performed using high-speed video microscopy on exposed ciliated surfaces, usually requiring the dissection of the relevant organ to image the cilia. This approach, however, is invasive and disturbs the natural ciliary environment, leading to inaccurate interpretations. In recent years, several methods utilizing OCT for studying motile cilia have been introduced. These methods enable mapping cilia locations, analyzing cilia beat frequencies, and mapping microflows induced by cilia. Our new method is the first to facilitate the analysis of cilia coordination, specifically the metachronal wave, through tissue layers. Our method is unique for studying their collective movement, as there is currently no alternative technology offering such depth-resolved measurements. This innovation has enabled us to map the propagation of the cilia metachronal wave within the lumen of the mouse fallopian tube without disrupting the normal physiological environment — a capability previously unavailable. What is the next step in your research? Motile cilia play a crucial role in regulating physiological processes throughout the body. Given recent advancements in clinical endoscopic OCT imaging of the upper airway, the immediate and prominent application is likely to be in diagnosing pathologies related to the coordination of ciliary activity in the respiratory system. Researchers could explore the function of motile cilia in regulating fluid flows within brain ventricles. This could be investigated in vivo using our method in small animal models, such as zebrafish or mice. Analyzing coordinated ciliary function in the embryonic brain under normal and pathological conditions (including genetic models or exposure to environmental factors or substances of abuse) could yield new insights into normal brain function and congenital and developmental neurological disorders. Our method is particularly well suited for studying coordinated cilia function in the fallopian tube of mouse models. Mouse models serve as invaluable resources in health care, offering thousands of genetic and epigenetic preclinical models to study human diseases, along with an established pipeline for translating knowledge from mouse models into clinical practice. Although ciliopathies are implicated in ectopic pregnancies, the precise role of cilia dynamics in embryo transport remains unclear. This method holds the potential to answer longstanding questions about the role of cilia in the normal physiology of the fallopian tube and the specific functional consequences of ciliopathies. Our group aims to further the understanding of cilia dynamics.
