Mechanosensory hair cells are the receptor cells of hearing and balance. Hair cells are sensitive to death from exposure to therapeutic drugs with ototoxic side effects, including aminoglycoside antibiotics and cisplatin. We recently showed that the induction of heat shock protein 70 (HSP70) inhibits ototoxic drug-induced hair cell death. Here, we examined the mechanisms underlying the protective effect of HSP70. In response to heat shock, HSP70 was induced in glia-like supporting cells but not in hair cells. Adenovirus-mediated infection of supporting cells with Hsp70 inhibited hair cell death. Coculture with heat-shocked utricles protected nonheatshocked utricles against hair cell death. When heat-shocked utricles from Hsp70 -/-mice were used in cocultures, protection was abolished in both the heat-shocked utricles and the nonheat-shocked utricles. HSP70 was detected by ELISA in the media surrounding heat-shocked utricles, and depletion of HSP70 from the media abolished the protective effect of heat shock, suggesting that HSP70 is secreted by supporting cells. Together our data indicate that supporting cells mediate the protective effect of HSP70 against hair cell death, and they suggest a major role for supporting cells in determining the fate of hair cells exposed to stress.

Many studies that aim to investigate the underlying mechanisms of hearing loss or balance disorders focus on the hair cells and spiral ganglion neurons of the inner ear. Fewer studies have examined the supporting cells that contact both of these cell types in the cochlea and vestibular end organs. While the roles of supporting cells are still being elucidated, emerging evidence indicates that they serve many functions vital to maintaining healthy populations of hair cells and spiral ganglion neurons. Here we review recent studies that highlight the critical roles supporting cells play in the development, function, survival, death, phagocytosis, and regeneration of other cell types within the inner ear. Many of these roles have also been described for glial cells in other parts of the nervous system, and lessons from these other systems continue to inform our understanding of supporting cell functions.

Hearing loss and balance disorders affect millions of people worldwide. Sensory transduction in the inner ear requires both mechanosensory hair cells (HCs) and surrounding glia-like supporting cells (SCs). HCs are susceptible to death from aging, noise overexposure, and treatment with therapeutic drugs that have ototoxic side effects; these ototoxic drugs include the aminoglycoside antibiotics and the antineoplastic drug cisplatin. Although both classes of drugs are known to kill HCs, their effects on SCs are less well understood. Recent data indicate that SCs sense and respond to HC stress, and that their responses can influence HC death, survival, and phagocytosis. These responses to HC stress and death are critical to the health of the inner ear. Here we have used live confocal imaging of the adult mouse utricle, to examine the SC responses to HC death caused by aminoglycosides or cisplatin. Our data indicate that when HCs are killed by aminoglycosides, SCs efficiently remove HC corpses from the sensory epithelium in a process that includes constricting the apical portion of the HC after loss of membrane integrity. SCs then form a phagosome, which can completely engulf the remaining HC body, a phenomenon not previously reported in mammals. In contrast, cisplatin treatment results in accumulation of dead HCs in the sensory epithelium, accompanied by an increase in SC death. The surviving SCs constrict fewer HCs and display impaired phagocytosis. These data are supported by in vivo experiments, in which cochlear SCs show reduced capacity for scar formation in cisplatin-treated mice compared with those treated with aminoglycosides. Together, these data point to a broader defect in the ability of the cisplatin-treated SCs, to preserve tissue health in the mature mammalian inner ear. . 4 SCs perform many functions, including providing critical trophic factors, preventing excitotoxicity, and mediating regeneration in those systems (non-mammalian vertebrates) capable of replacing lost HCs. 5-11 When HCs die, SCs also preserve the integrity and function of the remaining tissue by forming scars and clearing dead HCs. 2,12-17 Maintaining a fluid barrier at the surface of the sensory epithelium after damage is necessary to preserve the electro-chemical gradient that drives HC depolarization and therefore sensory transduction after the onset of hearing (reviewed in Wangemann). 18 Several major stressors cause HC death, 19-22 including aging, noise trauma, and exposure to therapeutic drugs with ototoxic side effects. When a HC is killed by noise or aminoglycoside antibiotics, surrounding SCs form a filamentous actin (F-actin) cable that constricts the HC at its apex. 2,[12][13][14][15][16][17] This process separates the apical portion of the cell, including the stereocilia bundle, from the HC body and preserves a sealed reticular lamina. 23 In the chick utricle, following the apical constriction of dead HCs, the SCs engulf and phagocytose the remaining HC corpse. 15 Additional data from the chick indicate that the ototoxi...

Objective-The lack of therapies that inhibit valvular calcification and the conflicting outcomes of clinical studies regarding the impact of 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase inhibitors on valve disease highlight the need for controlled investigations to characterize the interactions between HMG-CoA reductase inhibitors and valve tissue. Thus, we applied multiple in vitro disease stimuli to valvular interstitial cell (VIC) cultures and examined the impact of simvastatin treatment on VIC function. Methods and Results-VICs were cultured on 3 different substrates that supported various levels of nodule formation.Transforming growth factor (TGF)-␤1 was also applied as a disease stimulus to VICs on 2-D surfaces or encapsulated in 3-D collagen gels and combined with different temporal applications of simvastatin. Simvastatin inhibited calcific nodule formation in a dose-dependent manner on all materials, although the level of statin efficacy was highly substrate-dependent. Simvastatin treatment significantly altered nodule morphology, resulting in dramatic nodule dissipation over time, also in a substrate-dependent manner. These effects were mimicked in 3-D cultures, wherein simvastatin reversed TGF-␤1-induced contraction. Decreases in nodule formation were not achieved via the HMG-CoA reductase pathway, but were correlated with decreases in ROCK activity. Conclusions-These studies represent a significant contribution to understanding how simvastatin may impact heart valve calcification. Key Words: heart valves Ⅲ valvular interstitial cells Ⅲ simvastatin Ⅲ calcification Ⅲ extracellular matrix C alcification is the major cause of aortic heart valve failure and is the most common heart valve disorder in developed countries. 1 Currently, there are no medical agents that are FDA-approved to halt the progression of aortic valve disease. 2 Valvular interstitial cells (VICs) are fibroblast-like cells that comprise the bulk of the valve that are believed to be the predominant cell type involved in valve calcification. 1,3 Calcified heart valves are rich in activated VICs, also known as myofibroblasts, as well as osteogenic growth factors and cytokines, including bone morphogenetic proteins (BMPs) and TGF-beta1 (TGF-␤1). [3][4][5] Diseased valves also display grossly altered extracellular matrix (ECM) composition and arrangement. 6 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase inhibitors have been associated with reduced mortality in patients with atherosclerotic disease. 7-9 Despite the intended purpose of lowering LDL serum cholesterol levels, HMG-CoA reductase inhibitors appear to have pleiotropic cholesterol-independent effects such as antioxidation, improvement of endothelial function, and modulation of proinflammatory cytokine production. 10 -12 In some studies, this type of drug treatment was found to slow the progression of valvular stenosis in patients with atherosclerosis. [13][14][15][16] However, the numerous-and often conflicting-clinical studies that have examined the relation...