Tilapia prolactin cells are thermosensitive osmoreceptors

Abstract

Prolactin (PRL) cells within the rostral pars distalis (RPD) of euryhaline and eurythermal Mozambique tilapia, Oreochromis mossambicus, rapidly respond to a hyposmotic stimulus by releasing two distinct PRL isoforms, PRL188 and PRL177. Here, we describe how environmentally relevant temperature changes affected mRNA levels of PRL188 and PRL177 and the release of immunoreactive prolactins from RPDs and dispersed PRL cells. When applied under isosmotic conditions (330 mOsm/kg), a 6 °C rise in temperature stimulated the release of PRL188 and PRL177 from both RPDs and dispersed PRL cells under perifusion. When exposed to this same change in temperature, ~50% of dispersed PRL cells gradually increased in volume by ~8%, a response partially inhibited by the water channel blocker, mercuric chloride. Following their response to increased temperature, PRL cells remained responsive to a hyposmotic stimulus (280 mOsm/kg). The mRNA expression of transient potential vanilloid 4, a Ca2+-channel involved in hyposomotically-induced PRL release, was elevated in response to a rise in temperature in dispersed PRL cells and RPDs at 6 and 24 h, respectively; prl188 and prl177 mRNAs were unaffected. Our findings indicate that thermosensitive PRL release is mediated, at least partially, through a cell-volume dependent pathway similar to how osmoreceptive PRL release is achieved.

Temperature modulates the osmosensitivity of tilapia prolactin cells

“…Stemming from the recent nding that tilapia Prl cells are thermosensitive 27 in addition to their well established role in osmoreception, the present study examined the interactions between osmotic and thermal stimuli in Prl cells of Mozambique tilapia acclimated to either FW or SW. Our ndings indicate that: 1) A rise in temperature increases Prl release in-vitro as early as 1 h; 2) The osmotic-sensitivity of Prl release is lost at 20°C; 3) Tilapia acclimated to SW are more responsive to changes in temperature than those acclimated to FW; 4) prlr2 expression is inversely related with circulating levels of Prl and is inhibited by a rise in temperature; 5) trpv4 responded differentially to temperature depending on the acclimation salinity of sh; 6) Most of the TF transcripts in Prl cells of SW-acclimated tilapia decrease their mRNA levels in response to an elevation in termperature.…”

“…Mozambique tilapia Prl cells are osmoreceptors 7 which have been recently described to also respond to physiologically relevant increases in temperature by increasing Prl release 27 . The control of Prl release by environmental salinity, in vivo, and extracellular osmolality, in vitro, is well studied 17,19,49,50 .…”

“…Previous studies have shown that low temperatures (15°C) reduces the salinity tolerance of Mozambique tilapia and its hybrids 46,47 . The expression of trpv4, is elevated by temperature in chum salmon (Oncorhynchus keta) 48 and Mozambique tilapia Prl cells 27 , further reinforcing the crosstalk between thermal and osmotic stimuli in the regulation of Prl synthesis and release. While the tilapia Prl cell model has allowed for the identi cation of several downstream components involved in the transduction of hyposmotic stimuli into Prl secretion, little is known on how temperature interacts with extracellular osmolality in the regulation of prl transcription.…”

“…Consequently, hyposmotically-induced prl expression is more responsive in tilapia acclimated to SW than those in FW 17,26 . Recently, we reported that tilapia Prl cells are also thermosensitive 27 . Insamuch as Mozambique tilapia is both euryhaline and eurythermal, surviving in salinities ranging from FW to over double-strength SW and temperatures between 10-38°C 28 , it is likely that both thermal and osmotic stimuli interact during adaptive hormonal responses.…”

“…Prl also exerts autocrine responses on Prl cells which are in turn modulated by extracellular osmolality 36 . Thermally-induced Prl release also appears to operate through a cell-volume dependent mechanism 27 . The mechanistic commonalities between hyposmotically-and thermally-induced release of Prls, raise the question of whether similar mechanisms are present in the regulation of prl genes.…”