Expression of heat shock proteins in anoxic crucian carp (Carassius carassius): support for cold as a preparatory cue for anoxia

Abstract

The crucian carp (Carassius carassius) tolerates anoxia for days to months depending on temperature. During episodes of stress, heat shock proteins (HSPs) are important for limiting cellular damage, mainly by ensuring protein function. Accordingly, we hypothesized that anoxia would change the expression of HSPs and that this response would be temperature dependent. Real-time RT-PCR was used to investigate the effects of 1 and 7 days anoxia (A1 and A7) on the expression of HSP70a, HSP70b, HSC70, HSP90, and HSP30 in the brain and heart of 8 degrees C- and 13 degrees C-acclimated crucian carp. In general, the expression of all HSPs changed in response to anoxia, although varying in size and direction, and with organ and temperature. HSP70a expression increased drastically (approximately 10-fold) in A7 brains and hearts at 13 degrees C but not at 8 degrees C. HSC70 and HSP90 expression decreased in A7 brains (by 60-70%), but not in A7 hearts. HSC70 expression increased in A1 brains and hearts at both temperatures (by 60-160%), and HSP30 expression decreased in A7 brains and hearts at both temperatures (by 50-80%). Notably, normoxic fish showed 7- and 11-fold higher HSP70a expression in the brain and heart at 8 degrees C compared with 13 degrees C. This difference disappeared during anoxia, suggesting that cold may function as a cue for preconditioning the crucian carp's HSP70a expression to the approaching anoxic winter period.

Effects of prolonged anoxia on electrical activity of the heart in Crucian carp (Carassius carassius)

“…Low temperature pre-conditions cardiac E-C coupling for winter by altering gene activity Although the significance of low temperature in adjusting crucian carp physiology for winter anoxia is documented by several previous studies (Vornanen, 1994b;Tiitu and Vornanen, 2001; Rissanen et al, 2006;Stensløkken et al, 2010;Varis et al, 2016), this is the first study to examine the effects of temperature and anoxia on transcript expression of E-C coupling genes. Comparison of expression data between summer-and winter-acclimatised crucian carp indicates large differences in the activity of genes contributing to the molecular machinery of cardiac E-C coupling, similar to previous reports for crucian carp acclimated to different temperatures in the laboratory (Hassinen et al, 2008b(Hassinen et al, , 2011Korajoki and Vornanen, 2014).…”

“…Lowering temperature is the seasonal cue that usually pre-conditions these fish for winter, e.g. by stimulating glycogen storage and modifying the cardiac excitation-contraction (E-C) coupling machinery (Tiitu and Vornanen, 2001;Rissanen et al, 2006;Stensløkken et al, 2010;Varis et al, 2016). The heart of summer-acclimatised crucian carp responds to short-term oxygen shortage (1-16 h) at +20°C with a strong bradycardic reflex, which is mediated by increased cholinergic tone (Vornanen, 1994b;Vornanen and Tuomennoro, 1999).…”

Dramatic increase of nitrite levels in hearts of anoxia-exposed crucian carp supporting a role in cardioprotection

“…It has been found that crucian carp use low temperature as a preparatory cue for anoxia (77). For example, the expression of the cytoprotective heat shock protein HSP70 increases in anoxia in warm acclimated fish, whereas it is already increased in normoxia in cold acclimated fish (70). This is especially interesting, because nitrite has been found to upregulate the expression of HSP70 (7).…”

Heat shock proteins and hypometabolism: adaptive strategy for proteome preservation

“…Expression of all genes showed anoxia-induced changes varying in size and direction, as well as with organ and temperature. 61 For example, hsp70a transcripts increased ∼10-fold in the brain and heart after 7 hours of anoxia at 13°C whereas hsc70 increased after 1 hour of anoxia in both organs at both temperatures. Of particular interest, normoxic fish showed 7-and 11-fold higher expression of hsp70a in both organs in cold (8°C) compared with warm (13°C) water.…”

“…61 Anoxia tolerance allows carp to survive in ice-locked small ponds that become oxygen-depleted over the winter months. A unique metabolic strategy aids their survival; carp avoid metabolic poisoning by lactic acidosis by catabolizing lactate to ethanol and CO 2 that are both excreted.…”