The important role of protamine in spermatogenesis and quality of sperm: A mini review

Muslim Akmal, Aulanni’am Aulanni’am, M. Aris Widodo, Sutiman B. Sumitro, Basuki B. Purnomo, Widodo*

1Faculty of Veterinary Medicine, Syiah Kuala University, Banda Aceh, Aceh, Indonesia

2Faculty of Veterinary Medicine. Brawijaya University, Malang, East Java, Indonesia

3Medicine Faculty, Brawijaya University, Malang, East Java, Indonesia

4Biology Department, Faculty of Mathematics and Natural Science. Brawijaya University, Malang, East Java, Indonesia

The important role of protamine in spermatogenesis and quality of sperm: A mini review

Muslim Akmal1*, Aulanni’am Aulanni’am2, M. Aris Widodo3, Sutiman B. Sumitro4, Basuki B. Purnomo3, Widodo4*

1Faculty of Veterinary Medicine, Syiah Kuala University, Banda Aceh, Aceh, Indonesia

2Faculty of Veterinary Medicine. Brawijaya University, Malang, East Java, Indonesia

3Medicine Faculty, Brawijaya University, Malang, East Java, Indonesia

4Biology Department, Faculty of Mathematics and Natural Science. Brawijaya University, Malang, East Java, Indonesia

ARTICLE INFO

Article history:

Received 2016

Received in revised form 2016

Accepted 2016

Available online 2016

Sperm

Inhibin B

Protamine

Spermatogenesis

Male fertility

Objective:To prove that the decrease in the expression of protamine 2 affects the fertilization ability and the number of child production.Methods:During the development stage of elongating spermatids, human spermatozoa chromatin undergo a complex transition where histone is extensively replaced by protamine. Histone substitution by protamine 1 and 2 plays a significant role in condensing chromatin required to induce the quality of potent spermatozoa. The substitution also has a key role in protecting spermatozoa from effects of free radicals which can degrade the spermatozoa quality.Results:The results revealed that protamine deficiency instigated a severe disruption of spermatogenesis affecting male infertility. In addition, the protamine expression disorder caused a decrease in number, motility, and morphology of spermatozoa.Conclusion:Our results of a study in mice confirmed that inhibin B injection caused a reduction in the expression of protamine 2 in cauda epididymis. It has implications in the decrease of motility, concentration, and spermatozoa viability so that it affects the fertilization ability and the number of child production.

1. Introduction

Spermatogenesis in mammals is a complicated process involving the division and differentiation of spermatogonial stem cells into mature spermatozoa. The spermatogenesis process consists of several phases, namely the mitosis proliferation of spermatogonial stem cells to produce spermatocytes, the division of spermatocyte meiosis to produce haploid round-spermatids, and the spermiogenesis or final stage involving the early stages of round spermatids to be mature elongated-spermatids[1].

During spermiogenesis, haploid spermatids undergo a series of changes in the composition and compactness of chromatin[2]. Meanwhile, in the round spermatid, the bond between deoxynucleic acid (DNA)-histone will be replaced by transition proteins, whereas in elongated spermatids, the transition protein will be replaced by protamine. Alterations from histone to protamine instigate spermatozoa chromatin condensation[3]. The process begins with changes of histone triggered by transition protein 1 and 2 and eventually replaced by protamine[4]. Alterations in transition proteins caused by protamine occur in the stage of elongating spermatid, and in humans, where 85% histone is replaced by protamine[2]. The content of protamine is indispensable for the final phase maturation of spermatozoa nucleus[5].

Facts reveal that a number of DNA in humans’ mature spermatozoa binds to protamine[6]. In mammals, substituting histone by protamine is crucial in condensing and solidifying DNAinto the spermatozoa head during spermatogenesis[7]. Somatic histone alterations by protamine result in a very compact DNA. It triggers the DNA in order to be protected from free radicals, such as free water and other compounds which are dissolved in water and causing the DNA damage[8]. Besides, alterations in a number of histones by protamine 1 (P1) and protamine 2 (P2) play a significant role in facilitating the compactness of chromatin package required for normal function of spermatozoa[9].

The results showed that the increase in protamine expression leads to the deterioration in the spermatozoa quality and reduces the embryogenesis quality in couples which undergo in vitro fertilization (IVF) / intracytoplasmic sperm injection (ICSI)[10]; on the other hand, defects of protamine gene cause the disability of spermatozoa DNA and male infertility[7]. [11] Torregrosa N, et al. found that the change of P1:P2 ratio within the spermatozoa leads to infertility. Moreover,[12] revealed the decrease in P2 expression in infertile male patients. It shows that P2 has a significant role in maintaining male’s fertility.

2. Spermatozoa protamine

Protamine has a key role in spermatozoa chromatin condensation. Its deficiency causes negative effects on morphology and male fertility. It shows that protamine is required in the design and function of spermatozoa[13]. Protamine is a basic core protein contained in the head of spermatozoa[14] with a molecular weight about 5 kDa–8 kDa[15]. The content of protamine in the core of spermatozoa’s head is vital to induce a compact spermatozoa chromatin condensation which is influential for male fertility[16].

In the core of spermatozoa’s head, there are P1 and P2[17]. P1 is synthesized as a mature protein, while P2 as a precursor[18], and they are located in the core of human’s spermatozoa head[19]. P1 is found in spermatozoa of all mammals, while P2 spermatozoa is in mice, hamsters, stallions, some primates and humans[2]. Data presented that P1 and P2 are the abundant core proteins contained in the spermatozoa’s head, and they function in packaging or protecting the male genome[20]. The results showed that the insufficiency of P1 or P2 causes infertility in mice, whereas P2 deficiency causes damage in spermatozoa’s DNA and embryo mortality [21]. In general, these proteins are involved in various spermatogenesis mechanisms and sperm motility (Figure 1).

Figure 1.Protein Network protamine (PRM1).PRM1 protein has linkage to several proteins accumulated in two biological mechanisms: regulation of actin filament polymerization (left cluster) and spermatogenesis (right cluster). Data was retrieved from String-DB.

3. Role of protamine in spermatozoa’s DNA abnormalities and disability

Fertilization involves a direct interaction amongst spermatozoa and oocytes, a merger of the cell membrane, and a union of male and female gamete genome[22]. The process can thoroughly take place when supported by the compact spermatozoa DNA integrity[23]. Spermatozoa’s DNA integrity plays a significant role in delivering accurate genetic information[24].

Spermatozoa’s DNA must be well protected, such as by somatic cell’s chromatin in order to be resistant toward nucleases[25]. Normally, spermatozoa’s chromatin is well structured, the structure is compact with DNA content, and the nucleoprotein is heterogeneous[26]. The compactness of spermatozoa chromatin is due to the bonding between DNA and proteins of core spermatozoa, particularly the protamine[27]. Various abnormal forms of spermatozoa’s chromatin or DNA damage result in male infertility [24]. Damages in spermatozoa’s DNA are supposed to play a role as an infertility biomarker[28]. A number of causes why spermatozoa DNA damages are the protamine deficiency, DNA fragmentation, and abnormal chromatin composition[29].

Protamine plays an important role in male’s normal fertility. The deficiency in P1 and P2 causes subfertile or severe infertile condition [10]. The results indicated that DNA damage in human spermatozoa produces the disruption of reproductive outcomes[30]. Damages in germ cells’ DNA can increase mutations which ultimately lead to birth defects, genetic diseases, and cancer[31]. Damages in spermatozoa’s DNA are considered to be closely related to the occurrence of male infertility and abnormal spermatogenesis[29]. An abnormal expression of protamine results in pathology connected with the spermatogenesis disruption[9].

4. Correlation between inhibin B and protamine

Inhibin is a glycoprotein hormone secreted by testis’ Sertoli cells [32]. Inhibin B is significantly secreted by the Sertoli cells of testes [33], and the most important form of inhibin in male[34]. Inhibin B secretion by Sertoli cells is stimulated by follicle stimulating hormone (FSH)[35], whereas inhibin B regulates the FSH secretion through negative feedback regulatory[36]. A feedback control system of FSH is significantly regulated by inhibin B[37].

The bond between FSH and its receptor (FSH-R) in Sertoli cells will induce the activation of five molecular pathways, namely cyclic adenosine monophosphate-protein kinase A (cAMP-PKA) pathway, calcium pathway, mitogen-activated protein (MAP) kinase pathway, phospholipase A2 pathway, and the phosphatidylinositol 3-kinase pathway. Three of five pathways, namely cyclic adenosine monophosphate-protein kinase A (cAMP-PKA) pathway, calcium pathway, and mitogen-activated protein (MAP) kinase pathway will induce the activation of cAMP-response element binding protein(CREB) in the nucleus of Sertoli cells[38]. Moreover, the cAMPPKA pathway also facilitated phosphorylation of cAMP-responsive element modulator (CREM) on the serine 117[39].

CREM has a key role in spermatogenesis[40]. The results showed that it is crucial in the development of human’s spermatids[41]. It is also required in regulating the gene expression in the haploid of spermatids[42]. Alterations in CREM expression interfere the spermatid maturation within a number of cases in idiopathic male infertility[41]. In addition, the results showed that there is a close link between the spermatid maturation disorder and the incidence of infertility in men[39,43]. The study also showed that mice with deficient CREM will affect the protamine expression, thus it causes infertility due to the disorder of round spermatid maturation[43].

Protamine, a major core protein of spermatozoa, also functions as DNA binder and compaction into the nucleus of spermatozoa head[44]. It is vital for the chromatin formation required in the normal function of spermatozoa[45]. An abnormal expression of protamine causes a decrease in the number of spermatozoa, in motility and morphology of spermatozoa, an increase of damage in spermatozoa chromatin[46], a decrease in the spermatozoa viability, in the damage of spermatozoa DNA[47] and male infertility[48]. The results showed that P2 is crucial in maintaining the integrity of human’s spermatozoa chromatin[21] whereas the deficiency of P2 is thought to be a contributing factor in producing immotile spermatozoa[49].

Our results in rats (Rattus novergicus) showed that the injection of inhibin B incites a decrease in the concentration of FSH[50], which in turn has implications for the decreased expression of CREM in testis tissue[51]. The reduction of CREM triggers a decrease in P2 expression within the spermatozoa’s head in the cauda epididymis. Thus it causes the decline in spermatozoa motility[52] in concentration and viability of spermatozoa[51]. Low motility of spermatozoa will reduce the spermatozoa ability to fertilize an egg cell[53,54]. Thus it decreases the number of children generated by in vivo fertilization[55].

We concluded that Fertilization requires good quality spermatozoa. Disturbances in spermatogenesis result in the low-quality production of spermatozoa. Protamine is the molecule responsible for the spermatozoa quality. Inhibin B injection causes a decrease in motility, concentration, viability of spermatozoa, and the decrease in the number of children generated by in vivo fertilization. It is due to the reduction of CREM expression in testis tissue, which in turn interferes in the P2 expression within the network of cauda epididymis. It confirms the importance of protamine role particularly P2 in maintaining spermatogenesis and spermatozoa quality as well as indicates the possible development of inhibin B as the candidate of male’s peptide-based hormonal contraception.

Conflict of interest statement

The authors declare that they have no conflict of interest.

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ment heading

10.1016/j.apjr.2016.07.013

*Corresponding author: Muslim Akmal, Faculty of Veterinary Medicine of Syiah Kuala University, E-mail: muslim_akmal70@yahoo.com. Widodo, Biology Department, Brawijaya University, E-mail: widodo@ub.ac.id