The main areas of study include 1) characterization of the alteration of carbohydrate and energy metabolism which accompany fetal and neonatal development; 2) aging and investigation of the physiological significance of such changes; and 3) the role of hormones which regulate these processes. Our goals are to characterize the processes, which are developmentally/age-related and hormonally-dependent, and promote the changes of each type of PFK subunit. We are studying regulation of the expression of the PFK genes and processing of the mRNA for each subunit. We are cloning and sequencing each PFK subunit cDNA and gene and studying the regulation of the tissue-specific expression of the genes for each subunit during aging and development. Another area of study investigates the mechanisms that promote normal development of sensorineural hearing and age-dependent alteration of hearing by furosemide which is particularly efficacious in managing congestive heart failure and renal disorders. Normal development of hearing is characterized by increased energy consumption of the structures of the chochlea which we have shown is related to increased expression of one of the PFK subunits. The use of furosemide is complicated by adverse reactions which include tinnitus and temporary or permanent hearing loss, especially in neonates. The severity and duration of furosemide-induced ototoxicity is age-associated, dose-dependent, and exacerbated by concurrent antibiotic administration and impaired ability to metabolize or excrete furosemide. Damage resulting from furosemide has been related to disruption of the integrity of the cochlear lateral wall cells, i.e., stria vascularis and spiral ligament, and the presence of fluid in the extracellular space. These areas of the inner ear are involved in the provision of K+ to the endolymph which is required to maintain the positive endocochlear potential and the development and maintenance of hearing. Although other complications could also be involved, recovery of hearing from furosemide-induced damage correlates with ability to reform intact lateral wall cell structures. Our studies with rats suggest a possible mechanism for the repair of the stria vascularis. We have found that there is an age-dependent turnover of lateral wall cells. Specifically, the marginal stria vascularis cells undergo a relatively high rate of apoptosis and no measurable proliferation. Replacement of the marginal cells is related to proliferation of the underlying basal and intermediate cells. The spiral ligament cell types also exhibit significant age-dependent differences in proliferation and apoptosis. This natural process appears to facilitate growth and development of these cells during maturation and serves a maintenance function in the mature animal. Also, it could be a mechanism for repair of oto-traumatic events which affect the lateral wall cells. We are testing three hypotheses related to the age-dependent length of recovery of the furosemide-damaged stria vascularis and spiral ligament. 1) Recovery of mature rats receiving furosemide from temporary hearing loss, as measured by auditory brain responses, is due to cell resistance and/or rapid recovery mediated by the mature cell replacement process. 2) Delayed recovery of hearing deprivation experienced by the furosemide-treated neonatal rat is related to cell sensitivity and/or inadequate cell replacement process. Testing the first and second hypotheses will necessitate establishment, at different ages, of the extent of furosemide-induced morphological changes of the different types of lateral wall cells and measurement of the incidence of proliferation and apoptosis of the different lateral wall cell types. 3) Noise which would not normally be oto-traumatic, such as exists in pediatric intensive care units, potentiates the ototoxicity of furosemide and may even affect normal development of hearing. To investigate this hypothesis, structures of the lateral wall of the cochlea from untreated, and variously treated rats at the ages prior and subsequent to maturation of hearing will be examined.

SELECTED REFERENCES:

Mhaskar, Y., Dunaway, G.A. Alteration of Subunit Protein, Synthesis, and mRNA during Neonatal Brain Development. Developmental Brain Res 85:54-57, 1995.

Yancey, G.C., Schultz, V., Cunningham, B.A., Dunaway, G.A., Corkey, B.E., Tornheim, K. Phosphofructokinase Isozymes in Pancreatic Islets and Clonal-Cells (INS-1). Diabetes, 44:1285, 1995.

Mhaskar, Y., Dunaway, G.A. Alteration of 6-Phosphofructo-1-kinase Subunit Protein, Synthesis Rates, and mRNA during Neonatal Development. Mech of Aging and Develop 86:161, 1996.

Lee, R., Mhaskar, Y., Rybak, L., Dunaway, G.A. Inhibition of Brain Phosphofructokinase by Furosemide, Assoc for Res in Otolaryngol 1996.

Armour, G.A., Mhaskar, Y., Whitworth, C., Helfert, R.H., Rybak, L.P., Dunaway, G.A. Immunohistochemical Analysis of Phosphofructokinase Subunits during Maturation of the Cochlea, Assoc for Res in Otolaryngol., 1998.

Armour, G.A., Mhaskar, Y., Whitworth, C., Helfert, R.H., Rybak, L.P., Dunaway, G.A., Characterization of PFK Subunit Proteins and Incidence of Apoptosis in Marginal Stria Vascularis Cells and the Outer Hair Cells of the Rat, Assoc for Res in Otolaryngol 1999.