Research On Properties And Role Of Sperm-spectific KSper Channel

The regulation of sperm function is known to be of great importance during fertilization,and ion channel plays a key role during the process.Sperm-specific KSper channel which is the principle potassium channel in mammalian sperm associates with sperm motility,membrane hyperpolarization,acrosome reaction and so on.The first paper about native KSper current was published in 2007,KSper was found to be a strong pH-sensitive and voltage-gated potassium channel.After that,Slo3-/-mice were generated and exhibited infertility.KSper current abolished in Slo3-/-sperm,suggesting that KSper acted as an indispensable role in male reproduction.KSper current can also be recorded in human sperm.The properties of human KSper is still controversial because it differs from that of mouse KSper.A previous study showed that human KSper could be activated by calcium but insensitive to pH of which the properties was similar to Slo1 channel(BK channel).However,another study showed that native human KSper is indeed actived by calcium and also exhibits weak sensitivity to intracellular alkalization.Human KSper channel exhibited different hallmark with mouse Slo3 because of the species diversity.In addition,human KSper was also found to exhibit a similar pharmacological property with both Slo1 and Slo3 channel.Thus,the property of human KSper is still unclear.How the pH and Ca2+ regulate the human KSper channel? Is there any synergetic effect between the two factor during regulation? Hence,it's the main objective to clarify the properties of human KSper in this study.Slo3-/-sperm exhibited abnormality of motility,acrosome reaction and regulatory volume decrease(RVD)function,showing KSper channel was involved in sperm function regulation.However,it remains unclear about the physiological and toxicological function of KSper channel in mammalian and the possible target by some extracellular factors to regulate the sperm function.In recent years,environmental endocrine disruptor chemicals(EDCs)draw more and more attention because of their toxicity to male reproductive system.As an estrogen analog,bisphenol A(BPA)is widely used in industry,daily-use production and medical supplies.Several studies found BPA could impair mouse reproduction and fertility.For example,BPA could result in reproductive organ malformation,decrease sperm production,sperm motility and so on.Furthermore,the BK channel which belongs to Slo family could be activated by BPA.We hypothesize that KSper channel could be targeted by BPA in mammalian sperm to impair sperm functions.Therefore,it's another problem needs to be solved to clarify the influence of BPA on mature sperm functions and ion channel.Membrane potential results detected by patch clamp showed that pH and Ca2+ contributed individually to the sperm membrane hyperpolarization,suggesting both of them regulated human KSper channel.Furthermore,pH and Ca2+ shared a regulation pathway,because the hyperpolarization amplitude induced by both pH and Ca2+ simultaneously is less than the sum of that induced by p H or Ca2+ individually.Human sperm membrane potential exhibited diverse action for different calcium source.The inconceivable phenomenon may result from the colocalization between KSper and CatSper detected by Co-IP.By that pattern,the local calcium near the complex may be higher than global sperm,so KSper channel could sense the calcium efficiently.In addition,sperm motility and acrosome reaction decreased in BPA-treated mice.Associated with these sperm functions,the CatSper current also decreased in BPAtreated mice,resulting from the decreased expression level of CatSper1-4 subunits.No impair about KSper was found in BPA-treated mice.The mouse sperm motility and acrosome reaction examined by CASA and CTC staining was also decreased by BPA in vitro,along with the significant inhibition of CatSper current.In addition,human sperm function was also impaired by BPA in vitro which may be involved in other pathway rather than KSper and CatSper,because the two channels were both insensitive to BPA.Taken together,we suggested that human KSper channel could be regulated by both two physiological factors pH and Ca2+.As a key factor in regulating sperm functions,mouse CatSper could be targeted by physiological or toxilogical factor such as BPA.