Occurrence and possible role of heat shock protein 70 in the developing sea bass Dicentrarchus labrax (L.).

Heat shock proteins (HSPs) are cellular proteins highly conserved to polypeptide folding, identified in cells subjected to high temperature (as the name indicate). Many members of three families (HSP90, HSP70 and HSPs with low molecular weight) are present in both invertebrates and vertebrates, including the fish. The production of HSPs is one of the most common ways cell responds to a stressor to maintain its integrity and function. From several years we have been undertaking immunohistochemical studies on the appearance and distribution of regulatory molecules during the larval stages of the sea bass, a fish widely studied for its commercial value. In this study the results of immunolocalization of HSP70 in sea bass larvae, both in control and in specimens subjected to a biological stressor (LPS), are reported. The results showed a different pattern of immunoreactivity (IR) in LPS-treated vs. untreated sea bass larvae. LPS stress increases the amount of HSP70-IR in cells of skin, gills, terminal gut, liver and pituitary gland and induces the expression of HSP70 in the kidney collecting ducts; these effects are particularly evident in a short time (1 h). The present immunohistochemical data on the sea bass larvae suggest an involvement in stress-induced HSP-response of liver, gut, skin, gills, kidney collecting ducts and pituitary gland. In previous our research it has been hypothesized that some molecules involved in stress responses, such as ACTH, nitric oxide and CRF, may play an active role, via autocrine/paracrine ways, in early immune responses of sea bass larvae, before the complete development of gut-associated lymphoid tissue (GALT). This hypothesis comes from observations of IR to these molecules in gut epithelium, liver, pronefric tubules, skin and from the different pattern of IR following LPS treatment carried out with the same experimental design as in the present work. In particular, the distribution of IR to HSP70 in 24 day-old larvae LPS treated is very similar to that described previously for ACTH-IR in the same larval stages LPS treated. The data of present work may indicate that HSP70 also is a member of the pool of molecules involved in the early immune responses of larval sea bass. In the present research it has also been demonstrated, first in teleosts, HSP70-IR in untreated sea bass pituitary gland and its increase after LPS stress. HSP expression is already known for mammals. These data support the idea of a functional relationship between HSP expression and the hypothalamus-pituitary-adrenal axis that could be a common trait for vertebrates.