Molecular Mechanism Of HIF-1 Regulating Innate Immunity In Caenorhabditis Elegans Under Candida Albicans Infection

Candida albicans(C.albicans)is an opportunistic fungal pathogen.Normally,it has no pathogenicity as fungal symbiont,but candidiasis preys to those whose immune systems are compromised,which will pose a great threat to human health.As the virulence mechanisms of C.albicans are complex and diverse,it is particularly important to understand the molecular mechanisms related to pathogen recognition and host immune response during C.albicans infection.Caenorhabditis elegans(C.elegans)is not only a good model to study the interaction between host and microorganisms,but also an excellent model organism to explore the molecular mechanism of innate immunity.The hypoxia-inducible factor HIF-1 of C.elegans is highly homologous to human HIF-1α,which can be activated and regulate the body’s response under hypoxia,and is widely involved in the regulation of innate immunity.However,it is still unclear whether HIF-1 plays an immunoregulatory role in C.albicans infection and its immune mechanism in response to the pathogen.This study uses C.elegans as the experimental model to explore it,and the main research results are as follows:The involvement of C.elegans HIF-1 in the innate immune response induced by C.albicans was first discussed.At the transcriptional level,q RT-PCR results showed that the expression of hif-1 increased after C.albicans infection,and the difference was most significant at 12 h after infection.At the protein level,by detecting the fluorescence intensity of transgenic nematodes expressing HIF-1 labeled with green fluorescent protein,it was found that the change of HIF-1 protein level was consistent with the transcription level.Using lifespan,antimicrobial peptide gene expression and CFU(colony forming unit)as the evaluation endpoints,hif-1 knockdown nematodes had significantly shortened lifespan,reduced antimicrobial peptide gene expression,and increased CFU,which showed more sensitive to C.albicans infection.HIF-1 is expressed in the epidermis,muscle,intestine,neurons and gonads of nematodes,hif-1RNAi is carried out in different tissues.The results show that HIF-1 mainly modulate innate immune in the intestine.Therefore,the overexpressed hif-1 nematode Is(Pges-1-hif-1)was constructed by helium particle bombardment.By detecting the innate immune indicators,we found nematodes strengthened resistance capability for C.albicans infection after the overexpression of hif-1 in the intestine.This result suggests that the overexpression of hif-1 may activate the innate immunity towards C.albicans infection.The molecular mechanism of HIF-1 effect was further explored.Through the analysis of lifespan and abf-2 expression,hif-1 RNAi could significantly inhibit the resistance phenotype of Is(Pges-1-daf-16)and Is(Pges-1-pmk-1)nematodes to C.albicans,indicating that HIF-1 plays in the downstream of DAF-16,the key factor of intestinal insulin signal pathway,and PMK-1,the key factor of p38 MAPK signal pathway.We further screened the genes that interact with HIF-1 and participate in the immune response of C.albicans after infection,including C-type lectin coding gene clec-67,antimicrobial peptide coding gene cnc-4,cytochrome P450 family coding gene cyp-37B1,fatty acid desaturase 5 coding gene fat-5,and lysozyme coding gene lys-7,and they all participate in the immune regulation downstream of HIF-1.This study also found that after C.albicans infection,cyp-37B1 RNAi could reverse the ROS decrease caused by Is(Pges-1-hif-1),and fat-5 RNAi could reverse the fat increase caused by hif-1 RNAi,indicating that HIF-1 can activate the expression of cyp-37B1 and participate in the regulation of innate immunity by oxidative stress.At the same time,HIF-1 can also down-regulate fat-5 to reduce the amount of fat in nematodes to regulate innate immunity.In conclusion,this study revealed that hypoxia-inducible factor HIF-1 mainly regulates innate immunity in the intestine of C.elegans under C.albicans infection.HIF-1 was affected by insulin signaling pathway to regulate fat-5 and clec-67,and was also affected by p38 MAPK signaling pathway to regulate clec-67 and lys-7.HIF-1 also independently regulated the expression of downstream genes cnc-4 and cyp-37B1.C.elegans HIF-1 can jointly respond to C.albicans infection by regulating fat metabolism,immune defense and oxidative stress.This study provides a scientific basis for HIF-1as a potential target for the treatment of diseases caused by C.albicans infection,and provides ideas and reference for exploring other factors to participate in innate immune response from a more comprehensive perspective.