Heat shock response in noise-induced hearing loss: effects of alanyl-glutamine dipeptide supplementation on heat shock proteins status / Resposta de choque térmico em perda auditiva induzida por ruído: efeitos da suplementação com dipeptídeos de alanil-glutamina sobre o estado das proteínas de choque térmico

Abstract Introduction: The 72 kDa heat shock protein, HSP72, located intracellularly provides cochlear cytoprotective and anti-inflammatory roles in the inner ear during stressful noise challenges. The expression of intracellular HSP72 (iHSP72) can be potentiated by alanyl-glutamine dipeptide supplementation. Conversely, these proteins act as pro-inflammatory signals in the extracellular milieu (eHSP72). Objective: We explore whether noise-induced hearing loss promotes both intracellular and extracellular HSP72 heat shock response alterations, and if alanyl-glutamine dipeptide supplementation could modify heat shock response and prevent hearing loss. Methods: Female 90 day-old Wistar rats (n = 32) were randomly divided into four groups: control, noise-induced hearing loss, treated with alanyl-glutamine dipeptide and noise-induced hearing loss plus alanyl-glutamine dipeptide. Auditory brainstem responses were evaluated before noise exposure (124 dB SPL for 2 h) and 14 days after. Cochlea, nuclear cochlear complex and plasma samples were collected for the measurement of intracellular HSP72 and extracellular HSP72 by a high-sensitivity ELISA kit. Results: We found an increase in both iHSP72 and eHSP72 levels in the noise-induced hearing loss group, which was alleviated by alanyl-glutamine dipeptide treatment. Furthermore, H-index of HSP72 (plasma/cochlea eHSP72/iHSP72 ratio) was increased in the noise-induced hearing loss group, but prevented by alanyl-glutamine dipeptide treatment, although alanyl-glutamine dipeptide had no effect on auditory threshold. Conclusions: Our data indicates that cochlear damage induced by noise exposure is accompanied by local and systemic heat shock response markers. Also, alanyl-glutamine reduced stress markers even though it had no effect on noise-induced hearing loss. Finally, plasma levels of 72 kDa heat shock proteins can be used as a biomarker of auditory stress after noise exposure.

Resumo Introdução: A proteína de choque térmico de 72 kDa, HSP72 localizada intracelularmente, tem papéis citoprotetores e anti-inflamatórios cocleares na orelha interna durante situações de ruído estressantes. A expressão dessa proteína pode ser potencializada pela suplementação com dipeptídeo de alanil-glutamina. Por outro lado, essas proteínas atuam como sinais pró-inflamatórios no meio extracelular. Objetivo: Investigar se a perda auditiva induzida por ruído promove alterações tanto das proteínas HSP72 intracelulares quanto extracelulares na resposta de choque térmico e se a suplementação com alanil-glutamina pode modificar a resposta de choque térmico e evitar a perda auditiva. Método: Ratos Wistar fêmeas, com 90 dias de idade (n = 32), foram divididos aleatoriamente em quatro grupos: controle, perda auditiva induzida por ruído, tratados com alanil-glutamina e perda auditiva induzida por ruído mais alanil-glutamina. Os potenciais evocados auditivos do tronco encefálico foram avaliados antes da exposição ao ruído (124 dB NPS por 2 h) e 14 dias após. A cóclea, o complexo nuclear coclear e amostras de plasma foram coletadas para mensuração de HSP72 intra e extracelular com um kit Elisa de alta sensibilidade. Resultados: Houve um aumento nos níveis de HSP72 intra e extracelular no grupo perda auditiva induzida por ruído, que foi minimizado pelo tratamento com alanil-glutamina. Além disso, o índice H das HSP72 (razão HSP72 extracelular/HSP72intracelular plasma/cóclea) aumentou no grupo perda auditiva induzida por ruído, mas foi limitado pelo tratamento com alanil-glutamina, embora o alanil-glutamina não tenha efeito no limiar auditivo. Conclusões: Nossos dados indicam que o dano coclear induzido pela exposição ao ruído é acompanhado por marcadores da resposta de choque térmico locais e sistêmicos. Além disso, alanil-glutamina reduziu os marcadores de estresse, mesmo não tendo efeito sobre a perda auditiva induzida por ruído. Finalmente, os níveis plasmáticos de proteínas de choque térmico de 72 kDa podem ser usados como biomarcador do estresse auditivo, após a exposição ao ruído.

Chronic heat treatment positively impacts metabolic profile of ovariectomized rats: association with heat shock response pathways.

Low estrogen levels may predispose women to increased bodyweight and dyslipidemia. Previous studies from our laboratory suggest an involvement of depressed heat shock response (HSR) in this scenario because estrogen potently stimulates HSR. As heat treatment induces the expression of the anti-inflammatory heat shock proteins of the 70-kDa family (HSP70) and its accompanying HSR, we aimed to investigate whether chronic heat treatment promotes beneficial effects on biometric, lipid profile, oxidative stress, and HSR in ovariectomized rats. Wistar adult female rats (n = 32) were divided into four groups: control (C, n = 7), ovariectomized (OVX, n = 9), heat-treated (HT, n = 9), and heat-treated ovariectomized rats (OVX+HT, n = 7). HT and OVX+HT rats were anesthetized and submitted to heat treatment (once a week for 12 weeks) in a water bath (41 °C) to increase rats' rectal temperature up to 41 °C for 15 min, while C and OVX animals were submitted to a 36 °C water bath. HT attenuated the weight gain induced by OVX and increased HDL cholesterol and triglyceride serum levels. Also, OVX rats showed increased total cholesterol and LDL cholesterol levels that were not influenced by HT. Interestingly, it was found that an overall trend for HT to decrease tissue catalase and superoxide dismutase antioxidant activities was paralleled by a decrease in malondialdehyde levels (indicative of lower lipoperoxidation), especially in the skeletal muscle. Surprisingly, OVX was not able to depress intracellular HSP70 expression in the skeletal muscle, as expected, and this remained unchanged with HT. However, chronic HT did enhance intracellular HSP70 contents in white adipose tissue of OVX animals. As both glucose and insulin tolerance tests were not affected by OVX, which was not modified by HT, we suppose that estrogen absence alone is not sufficient to determine a state of insulin resistance associated with low intramuscular HSP70 content.