The impact of folate deficiency on the development of neural crest cells-derived tissues-the heart and melanocytes

Abstract

Folate (vitamin B9) is crucial for genome stability epigenetic regulation and redox balance Folate deficiency (FD) impedes neural crest development and has been correlated with many diseases such as neural tube defects (NTDs) congenital heart diseases (CHDs) and megaloblastic anemia However the mechanisms underlying these FD-associated disorders remain elusive In this study how FD impairs the development of heart and melanocyte two of the neural crest lineages was examined using FD-inducible zebrafish transgenic line Tg(hsp:EGFP-γGH) In the first part of this study the impact of FD on circulation development including cardiac development hematopoiesis and vascular integrity was examined We found impaired hematopoiesis including decreased hemoglobin level reduced erythrocyte number enlarged erythrocyte size and altered c-myb expression as well as cardiac defects including smaller chamber size increased heart rate reduced ejection fraction and altered cmlc2 expression in FD embryos/larvae Treating FD embryos with reduced form of folate 5-formyltetrahydrofolate (5-CHO-THF) or antioxidant N-acetyl-L-cysteine (NAC) ameliorated both hematopoietic and cardiac defects whereas nucleotide or Erk inhibitor ameliorated only the hematopoietic defects and the oxidized form of folate folic acid (FA) ameliorated only the cardiac defects These findings highlight the role of excessive oxidative stress in mediating FD-induced hematopoietic and cardiac defects and demonstrate that folate with reducing power serves as a better reliever to oxidative stress-dependent hematopoietic and cardiac defects resulted from FD In the second part of this study the impact of FD on the morphology and function of melanocytes was examined Melanocytes are the foundation of pigmentation and therefore indispensable for protecting organisms from ultraviolet (UV)-inflicted damage Maldevelopment of skin melanocytes including decreased melanogenesis reduced melanosome anterograde response and aberrant melanin dispersion was observed in FD larvae Treating FD larvae with 5-CHO-THF relieved both melanogenesis and melanosome transportation defects while FA failed to rescue the melanosome anterograde defects The aberrant melanin dispersion could be readily rectified when treating FD larvae with epinephrine one of the melanosome retrograde stimulus involved in the homeostasis of intracellular melanosome transportation Further examination of the melanocyte retrograde response and metabolite levels of epinephrine and its precursors suggested that reduced synthesis of dopamine a precursor of epinephrine contributes to the aberrant melanin dispersion observed in FD larvae Dopa decarboxylase (Ddc) is the enzyme catalyzing dopamine synthesis from L-dopa Decreased Ddc expression in both transcript and protein levels was observed in FD larvae Through injecting FD embryos with ddc construct the aberrant melanin dispersion was ameliorated These results demonstrate that FD impairs melanogenesis and melanosome transportation and reveal for the first time that down-regulated Ddc contributes to the aberrant melanin dispersion resulted from FD Along with the finding that FD disturbs melanocyte development the impact of folate statue on the vulnerability to UVB irradiation was investigated In comparison to control larvae FD larvae displayed more significant tail fin damage and ROS elevation after UVB irradiation indicating that FD leads to an increased susceptibility to UVB irradiation 5-CHO-THF in concordance with its efficacy in relieving melanocyte defects exerts better protection effects in ameliorating UVB-inflicted damage than FA Taken together these results demonstrate tissue-specific pathomechanisms resulted from FD Moreover the finding that 5-CHO-THF surpasses FA in relieving FD-inflicted developmental defects suggests that the biological availability is different between 5-CHO-THF and FA

Date of Award	2020
Original language	English
Supervisor	Tzu-Fun Fu (Supervisor)