As demonstrated previously, biochemical studies on rats (Mekhtiev 2000) and electrophysiological studies on the identified command neurons of snails (Mekhtiev et al. 2004) showed SMAP has a linear relationship with serotonin. This was identified first in the rat brain cortex and thereafter purified from the whole brain (Mekhtiev 2000).
Mass-spectroscopy analysis of SMAP revealed it to be composed of three proteins – dihydropyrimidinase-related protein 2 (DRP2; its other name – collapsin response mediator protein 2, CRMP2; Nakamura et al. 2020), actin and tubulin, which are bound tightly to each other by calcium-mediated bonds (Garina et al. 2018). The calcium nature of these bonds was shown by their sensitivity to the effects of 40 mM EDTA, which causes disruption and splits SMAP into the component proteins (Mekhtiev, unpublished data). The existence of such strong bonds between these proteins clarifies the observed behavior of SMAP as a single protein in protein fractionation by gel-chromatography (it is eluted as a single peak from the column Sephadex G-150), electrophoresis under non-denaturating conditions and western-blotting. As actin and tubulin are structural proteins of the cells, they, apparently, do not have regulatory activity and the observed nucleus-protective activity is, obviously, realized solely by DRP2.
On a whole, the results show upregulation of SMAP level in the tissues of the hens living in the districts with high levels of background γ-radiation along with a significant increase of nuclear pathologies in their erythrocytes and significant downregulation of cytochrome P-450 in their tissues. Furthermore, administration of SMAP to rats prior to their exposure to high doses of γ-radiation caused a significant decrease in the number of nuclear pathologies in their immature erythrocytes.
The results of controlled experiments carried out on rats, demonstrate that induced upregulation of SMAP through its administration to the animals provides significant protection of the nuclear apparatus of somatic cells from the damaging impact of high doses of γ-irradiation. These results are consistent with our earlier data showing the anti-mutagenic activity of SMAP. In those studies, administration of SMAP to fish prior to exposure to high levels of polyaromatic hydrocarbons and heavy metals decreased the level of mutagenic effects (micronucleus analysis; Schmid 1975) in somatic cells by 50% relatively to their levels in control animals (Mekhtiev & Movsum-zadeh 2008).
The above conclusion explains the significant upregulation of SMAP observed in the liver and kidney of the hens from settlements Binagady and Romany. SMAP provides protection for the animals to the high levels of γ-radiation background. It should be noted that despite the protective levels of SMAP, the high levels of γ-radiation at these settlements exerted strong adverse effects on the animals in the sense of sharp increases of nuclear pathologies in the erythrocytes and significant changes of the level of cytochrome P-450 in their tissues.
Earlier studies, carried out on the fish Alburnoides bipunctatus eichwaldi, a sedentary fish that lives in the rivers flowing through the territory of Azerbaijan, showed that a significant upregulation of SMAP in the tissues, accompanied by downregulation of cytochrome P-450, enhances adaptation of the animals to the impact of the toxin phenol. The concentration of phenol in the river water exceeded by 3 times the maximum permissible concentration (MPC). However, a higher concentration of phenol that exceeded the MPC by 4-fold resulted in a noticeable downregulation of SMAP in the fish tissues. This was likely due to the exhaustion of the animal’s adaptation potential (Mustafayev & Mekhtiev 2014). Based on these earlier studies, we conclude that the observed upregulation of SMAP in the tissues of the hens, living in settlements Binagady and Romany, reflects their adaptation to high doses of γ-radiation and, finally, their survival.
Our earlier studies, carried out on the animals of different species, including mice, rats and rabbits, showed that administration of SMAP significantly upregulates the level of HSP70 in their tissues (Ismailova & Mekhtiev 2018; Allahverdiyeva et al. 2019). HSP70 belongs to a group of chaperon proteins that are engaged in recovering the structure of the proteins damaged and denatured by the impact of various toxins (Sharp 1999, Daugaard et al. 2007). The results of the second series of the present studies and the data of other researchers show that 3- and 5-hour exposure times induce upregulation of HSP70 after SMAP administration or after exposure to heat shock (Wang et al. 2003). For this reason, in the third series of experiments the rats were subjected to the damaging effects of high dose of γ-radiation exactly 3 h after SMAP administration. These data provide an understanding for the possible molecular mechanisms of the protective activity of SMAP through upregulation of HSP70 which helps to alleviate the impact of γ-radiation and, consequently, decrease the level of nuclear pathologies of immature erythrocytes. At the same time, it indicates that SMAP provides for the adaptation and survival of the hens of settlements Binagady and Romany through the upregulation of HSP70 in the face of high levels of background γ-radiation.
Additionally, the results of our study and previous work allow us to hypothesize the existence of an alternative mechanism whereby SMAP protects cellular nuclei. Perhaps SMAP induces conformational changes to chromatin structure in which a condensed, and consequently more protective state, reduces the impact of radiation and prevents the formation of pathological changes to cellular nuclei. The possibility of such a protective mechanism is indicated, on one hand, by our earlier studies on the anti-mutagenic activity of SMAP in the model of pollutants-induced mutagenesis in the erythrocytes of fish (Mekhtiev and Movsum-zadeh 2008), and, on the other hand, by the evidence of a sharp increase of mutations in decondensed chromatin of somatic cells while passing through the phase of transcriptional activity (Jinks-Robertson 2014).