The Ricci Labs work ranges from furthering our understanding of both mechanotransduction, and how the sensory hair cells communicate with the central nervous system, to developing novel technologies and working with other researchers to provide technical insight, to the very exciting development of novel aminoglycoside antibiotics – a line of research which could significantly lessen the incidences of hearing loss, particularly in young children, from exposure to ototoxic drugs.
As part two of our series on the research currently being carried out in our labs: Dr. Anthony Ricci describes the innovative work currently underway in the Ricci Lab, as well as in collaboration with other SICHL labs and industry.
Themes of Research:
The Ricci lab has several major themes of research. The first, is understanding the molecular mechanisms and physiological significance of the first step in the hearing process, mechanotransduction. Mechanotransduction is how sound vibrations are converted into electrical signals by the sensory hair cell (see figure). The Ricci lab has a long history of novel and paradigm shifting findings on this topic including the demonstration that this process may be critical for frequency selectivity within the ear (Ricci and Fettiplace, 1997; Ricci et al., 2005) and localizing the channels to the tops of shorter stereocilia (see Figure) (Beurg et al.,2009) . We have demonstrated that mechanotransduction is important for setting the basal response of hair cells and contributes to the broad dynamic range, a hallmark of healthy audition (Farris et al., 2006). We have also provided a great deal of evidence as to the biophysical properties of this novel ion channel, work that has led to additional contributions when combating ototoxicity (see below) (Farris et al., 2004; Pan et al., 2012). We continually challenge the dogma as to how this system works and have made significant progress in elucidating the molecular mechanism and thereby new sites for intervention.
Ongoing projects include: characterizing the kinetics at which the mechanically gated channels can open and close, a project that will provide insight into how a mechanical stimulus is translated to this ion channel. A second project is evaluating the mechanical changes to the hair bundle that occur with channel stimulation and the role of calcium in altering these mechanical responses. This will provide insight into the molecular mechanisms of the process but also into how the system can be detrimentally effected at the molecular level by loud or persistent sounds. A third project, one that we feel may be paradigm shifting as to understanding the molecular mechanisms of mechanotransduction is, investigating the role of the lipid bilayer in translating force to the mechanosensitive ion channel. As mechanotransduction is often a site for genetic disorders, for noise, chemical and age related hearing loss, identifying the key molecules and mechanisms of action is critical for defining sites of intervention.
A second major direction of the laboratory is deciphering how the sensory hair cell communicates with the central nervous system. We know this happens through synaptic specializations termed ribbon synapses, but how this works at the molecular level remains a mystery. We are one of only a handful of laboratories that have the technical ability to investigate pre and postsynaptic responses from hair cells and their afferent fibers. We are using cutting edge, optical, electrophysiological and molecular tools to investigate how this system can transfer information regarding frequency, intensity and timing to the central nervous system with such high fidelity (Schnee et al., 2005; Schnee et al., 2011). As this synapse is often a site for damage via noise, age or chemically, identifying the molecules and mechanisms involved is critical to our ability to repair, restore and protect hearing.
In addition to these areas of research, we work closely with other members of the department to provide technical insight and physiological measurements, as needed. For example, we work with Stefan Heller and Alan Cheng to characterize cells deemed to be hair cell like in their quest to regenerate new sensory epithelium (Oshima et al., 2010). We are also working with Nik Blevins in developing strategies to image cochlear tissue in vivo. We are working with John Oghalai to investigate modulation of cochlear amplifier proteins. We are investigating developmental synaptic transmission questions with Mirna Mustapha. And finally, we are working with Sunil Puria on a variety of topics including modeling the mechanical movements of the inner ear tissue during sound stimulation and also modeling the role of the lipid bilayer on mechanotransduction. By incorporating the diverse skill sets in the department, we can create a research environment whose sum is greater than the individual components.
Novel Technology and Collaborative Development:
As a physiologist and biophysicist, Anthony Ricci and his lab, are focused upon understanding the cellular and molecular mechanisms that underlie the exquisite sensitivity and selectivity of the auditory system. By elucidating these mechanisms we can identify novel sites for intervention for the prevention and treatment of hearing loss.
One factor making our work unique is the incorporation of novel technology specifically designed to answer questions about the inner ear. By staying at the forefront of technological innovation, we are continually exploring and creating new levels of resolution from which to understand the auditory system.
For example, to identify the location of a particular ion channel responsible for mechanical sensitivity, we developed, in partnership with an external company, a high speed imaging system (Beurg et al., 2009). We then advanced this same imaging system further in order to explore how the sensory hair cell communicates with the afferent fibers (connecting to the brain) (Schnee et al., 2011).
When we were interested in directly monitoring how sensory hair cells communicate with the primary afferent neurons, we developed, in partnership with a colleague at Yale University, an electrophysiological tool that allows for direct tracking of synaptic vesicle fusion (Schnee et al., 2011). We are presently developing new electrophysiological devices that will provide unprecedented measures of how fast the auditory system can operate. These new tools come in the form of both stimulating and monitoring devices that allow us to probe the sensory cell at frequencies yet to be explored. This work is being done in partnership with faculty in the engineering school at Stanford, (Beth Pruitt) taking advantage of a rich collaborative environment.
Ongoing technological advances also include developing methodologies for imaging in vivo, the mechanical, biochemical and electrical workings of the cochlear cells. Aided by funding provided by NIH, and in collaboration with physicians in our department, engineers at Stanford and a private company, we are building new microscopes that will allow for cellular investigations in the whole animal environment.
Finally, with the collaborative efforts of a Stanford SPARK program, focused on creating medicinal pathways to the clinic, we are developing novel aminoglycoside antibiotics to alleviate the high rate of hearing loss, particularly in children, exposed to these chemicals at early ages.
Aminoglycoside antibiotics are the most commonly used antimicrobial agent worldwide, despite an incidence of hearing loss estimated at >20%. Our work on mechanotransduction led us to a novel hypothesis regarding these antibiotics, that they can enter sensory hair cells at a high rate via this channel but cannot exit (Farris et al., 2004; Waguespack et al., 2005). Working with Alan Cheng, we are using our intimate knowledge of the structure of the mechanically gated channel to design novel aminoglycosides that maintain their antimicrobial activity but lose their ototoxic effect (Abdelrahman et al., 2011). Remarkably we have been successful with one compound thus far and are in the process of completing testing on this compound, while developing additional compounds. We plan to use similar strategies with other ototoxic agents.
In April, Dr. Ricci presented a seminar, hosted by William Roberts, at the University of Oregon Institute of Neuroscience. The seminar was titled, “Evidence for synchronous release at a hair cell ribbon synapse In May, Dr. Ricci published, Permeation properties of the hair cell mechanotransducer channel provide insight into its molecular structure, in the Journal of Neurophysiology.