Microvasculature of the human testis in correlation to Leydig cells and seminiferous tubules

Molecular mechanisms of cellular dysfunction in testes from men with non-obstructive azoospermia

Male factor infertility affects 50% of infertile couples worldwide; the most severe form, non-obstructive azoospermia (NOA), affects 10-15% of infertile males. Treatment for individuals with NOA is limited to microsurgical sperm extraction paired with in vitro fertilization intracytoplasmic sperm injection. Unfortunately, spermatozoa are only retrieved in ~50% of patients, resulting in live birth rates of 21-46%. Regenerative therapies could provide a solution; however, understanding the cell-type-specific mechanisms of cellular dysfunction is a fundamental necessity to develop precision medicine strategies that could overcome these abnormalities and promote regeneration of spermatogenesis. A number of mechanisms of cellular dysfunction have been elucidated in NOA testicular cells. These mechanisms include abnormalities in both somatic cells and germ cells in NOA testes, such as somatic cell immaturity, aberrant growth factor signalling, increased inflammation, increased apoptosis and abnormal extracellular matrix regulation. Future cell-type-specific investigations in identifying modulators of cellular transcription and translation will be key to understanding upstream dysregulation, and these studies will require development of in vitro models to functionally interrogate spermatogenic niche dysfunction in both somatic and germ cells.

Three major reasons why transgenerational effects of radiation are difficult to detect in humans

PURPOSE

Ionizing radiation can induce mutations in germ cells in various organisms, including fruit flies and mice. However, currently, there is no clear evidence for the transgenerational effects of radiation in humans. This review is an effort to identify possible reasons for the lack of such observations.

METHODS

Literature search and narrative review.

RESULTS

1) In both mice and humans, resting oocytes locate primarily in the cortical region of the ovary where the number of blood vessels is very low especially when young and extra-cellular material is rich, and this region is consequently hypoxic, which probably leads to immature oocytes being resistant to the cell killing and mutagenic effects of radiation. 2) In studies of spermatogonia, the mouse genes used for specific locus test (SLT) studies, which include coat color genes, were hypermutable when compared to many other genes. Recent studies which examined over 1000 segments of genomic DNA indicate that the induction rate of deletion mutation per segment was on the order of 10-6 per Gy, which is one order of magnitude lower than that obtained from the SLT data. Therefore, it appears possible that detecting any transgenerational effects of radiation following human male exposures will be difficult due to a lack of mutable marker genes. 3) Fetal malformations were examined in studies in humans, but the genetic component in such malformations is low, and abnormal fetuses are prone to undergo miscarriage which does not occur in mice, and which leads to difficulties in detecting transgenerational effects.

CONCLUSION

The lack of clear evidence for radiation effects in humans probably does not result from any problem in the methodologies used but may be due largely to biological properties. Currently, whole genome sequencing studies of exposed parents and offspring are planned, but ethical guidelines need to be followed to avoid discrimination, which had once happened to the atomic bomb survivors.

The Quantum Theory of Reproduction – How Unique is an Individual?

Our understanding of nature’s way is founded on quantum mechanics. In its existence of over 80 years, quantum theory has been describing the physical world. The attraction of studying quantum mechanics is the perception of the conceptual structure of nature. This is aided by the mathematical structure that exposes the internal logic of the subject by inventing a notation that embeds the philosophy of the question. To describe how unique each individual is. A calculation method was applied. The uniqueness of an individual is one in two nonillion, octillion, septillion, sextillion, quintillion, quadrillion, trillion, billion, million and thousand. Individuals are indefinitely unique.

Heterogeneity and Dynamics of Vasculature in the Endocrine System During Aging and Disease

The endocrine system consists of several highly vascularized glands that produce and secrete hormones to maintain body homeostasis and regulate a range of bodily functions and processes, including growth, metabolism and development. The dense and highly vascularized capillary network functions as the main transport system for hormones and regulatory factors to enable efficient endocrine function. The specialized capillary types provide the microenvironments to support stem and progenitor cells, by regulating their survival, maintenance and differentiation. Moreover, the vasculature interacts with endocrine cells supporting their endocrine function. However, the structure and niche function of vasculature in endocrine tissues remain poorly understood. Aging and endocrine disorders are associated with vascular perturbations. Understanding the cellular and molecular cues driving the disease, and age-related vascular perturbations hold potential to manage or even treat endocrine disorders and comorbidities associated with aging. This review aims to describe the structure and niche functions of the vasculature in various endocrine glands and define the vascular changes in aging and endocrine disorders.

The Pluripotent Microvascular Pericytes Are the Adult Stem Cells Even in the Testis

The pericytes of the testis are part of the omnipresent population of pericytes in the vertebrate body and are the only true pluripotent adult stem cells able to produce structures typical for the tree primitive germ layers: ectoderm, mesoderm, and endoderm. They originate very early in the embryogenesis from the pluripotent epiblast. The pericytes become disseminated through the whole vertebrate organism by the growing and differentiating blood vessels where they remain in specialized periendothelial vascular niches as resting pluripotent adult stem cells for tissue generation, maintenance, repair, and regeneration. The pericytes are also the ancestors of the perivascular multipotent stromal cells (MSCs). The variable appearance of the pericytes and their progeny reflects the plasticity under the influence of their own epigenetic and the local environmental factors of the host organ. In the testis the pericytes are the ancestors of the neuroendocrine Leydig cells. After activation the pericytes start to proliferate, migrate, and build transit-amplifying cells that transdifferentiate into multipotent stromal cells. These represent progenitors for a number of different cell types in an organ. Finally, it becomes evident that the pericytes are a brilliant achievement of the biological nature aiming to supply every organ with an omnipresent population of pluripotent adult stem cells. Their fascinating features are prerequisites for future therapy concepts supporting cell systems of organs.

Origin and Differentiation of Androgen-Producing Cells in the Gonads

Sexual reproduction is dependent on the activity of androgenic steroid hormones to promote gonadal development and gametogenesis. Leydig cells of the testis and theca cells of the ovary are critical cell types in the gonadal interstitium that carry out steroidogenesis and provide key androgens for reproductive organ function. In this chapter, we will discuss important aspects of interstitial androgenic cell development in the gonad, including: the potential cellular origins of interstitial steroidogenic cells and their progenitors; the molecular mechanisms involved in Leydig cell specification and differentiation (including Sertoli-cell-derived signaling pathways and Leydig-cell-related transcription factors and nuclear receptors); the interactions of Leydig cells with other cell types in the adult testis, such as Sertoli cells, germ cells, peritubular myoid cells, macrophages, and vascular endothelial cells; the process of steroidogenesis and its systemic regulation; and a brief discussion of the development of theca cells in the ovary relative to Leydig cells in the testis. Finally, we will describe the dynamics of steroidogenic cells in seasonal breeders and highlight unique aspects of steroidogenesis in diverse vertebrate species. Understanding the cellular origins of interstitial steroidogenic cells and the pathways directing their specification and differentiation has implications for the study of multiple aspects of development and will help us gain insights into the etiology of reproductive system birth defects and infertility.

Human testicular peritubular cells secrete pigment epithelium-derived factor (PEDF), which may be responsible for the avascularity of the seminiferous tubules

Male fertility depends on spermatogenesis, which takes place in the seminiferous tubules of the testis. This compartment is devoid of blood vessels, which are however found in the wall of the seminiferous tubules. Our proteomic study using cultured human testicular peritubular cells (HTPCs) i.e. the cells, which form this wall, revealed that they constitutively secrete pigment epithelium-derived factor, PEDF, which is known to exert anti-angiogenic actions. Immunohistochemistry supports its presence in vivo, in the human tubular wall. Co-culture studies and analysis of cell migration patterns showed that human endothelial cells (HUVECs) are repulsed by HTPCs. The factor involved is likely PEDF, as a PEDF-antiserum blocked the repulsing action. Thus testicular peritubular cells, via PEDF, may prevent vascularization of human seminiferous tubules. Dihydrotestosterone (DHT) increased PEDF (qPCR) in HTPCs, however PEDF expression in the testis of a non-human primate occurs before puberty. Thus PEDF could be involved in the establishment of the avascular nature of seminiferous tubules and after puberty androgens may further reinforce this feature. Testicular microvessels and blood flow are known to contribute to the spermatogonial stem cell niche. Hence HTPCs via control of testicular microvessels may contribute to the regulation of spermatogonial stem cells, as well.

Gonadotropin-Mediated Regulation of the Murine VEGF Expression in MA-10 Leydig Cells

Presence of vascular endothelial growth factor (VEGF) is not only limited to cells directly involved in angiogenesis but has also been demonstrated in steroidogenic cells like testicular Leydig cells. Because Leydig cells are subjected to regulation by gonadotropic hormones and produce steroid hormones, we have investigated here the effects of human chorionic gonadotropin (hCG) or steroid hormones on VEGF expression in cultured mouse tumor Leydig cells (MA-10 cells) and have then analyzed the underlying molecular mechanisms. Northern blot analysis and enzyme-linked immunosorbent assays revealed increases in VEGF mRNA and protein levels, respectively, over 3-20 hours in MA-10 cells after stimulation with hCG or 8-Br-cAMP. Although MA-10 cells lack the classical progesterone receptor, progesterone was able to stimulate VEGF expression. Promoter analyses and antibody supershift experiments suggested that the proximal region is able to constitutively bind the transcription factors Sp1 and Sp3. Mutations of 2 potential Sp1 binding sites in the proximal region showed the requirement of these motifs for stimulation of VEGF by hCG and 8-Br-cAMP. The distal cytosine-rich sequence interacts with so far-unidentified faster migrating factors. Following stimulation with hCG or 8-Br-cAMP, the binding of these proteins was increased in the complexes formed in the proximal and distal regions. VEGF expression in Leydig cells is regulated by gonadotropin via a cAMP-dependent mechanism, and the transcription factors Sp1 and Sp3 appear to be involved in the activation of the promoter. Progesterone also appears to play a role in the regulation of VEGF, acting presumably via a nonconventional receptor that remains to be characterized yet.

Seasonal Changes in Testes Vascularisation in the Domestic Cat (Felis domesticus): Evaluation of Microvasculature, Angiogenic Activity, and Endothelial Cell Expression

Some male seasonal breeders undergo testicular growth and regression throughout the year. The objective of this study was to understand the effect of seasonality on: (i) microvasculature of cat testes; (ii) angiogenic activity in testicular tissue in vitro; and (iii) testicular endothelial cells expression throughout the year. Testicular vascular areas increased in March and April, June and July, being the highest in November and December. Testes tissue differently stimulated in vitro angiogenic activity, according to seasonality, being more evident in February, and November and December. Even though CD143 expression was higher in December, smaller peaks were present in April and July. As changes in angiogenesis may play a role on testes vascular growth and regression during the breeding and non-breeding seasons, data suggest that testicular vascularisation in cats is increased in three photoperiod windows of time, November/December, March/April and June/July. This increase in testicular vascularisation might be related to higher seasonal sexual activity in cats, which is in agreement with the fact that most queens give birth at the beginning of the year, between May and July, and in September.

Understanding spermatogenesis is a prerequisite for treatment

Throughout spermatogenesis multiplication, maturation and differentiation of germ cells results in the formation of the male gamete. The understanding of spermatogenesis needs detailed informations about the organization of the germinal epithelium, the structure and function of different types of germ cells, endocrine and paracrine cells and mechanisms, intratesticular and extratesticular regulation of spermatogenesis. Normal germ cells must be discriminated from malformed, apoptotic and degenerating germ cells and tumor cells. Identification of the border line between normal and disturbed spermatogenesis substantiate the diagnosis of impaired male fertility. The profound knowledge of the complicate process of spermatogenesis and all cells or cell systems involved with is the prerequisite to develop concepts for therapy of male infertility or to handle germ cells in the management of assisted reproduction.

Effect of varicocele on testicular artery blood flow in men--color Doppler investigation

OBJECTIVE

Varicocele can be defined as an abnormal tortuosity and dilatation of the veins of the pampiniform plexus. Contradictory results have been obtained from experimental animal models and a few clinical human studies on testicular arterial blood flow in varicocele. The purpose of this study was to determine the changes in testicular arterial blood flow parameters in patients with varicocele.

MATERIAL AND METHODS

A total of 62 patients with a clinical diagnosis of left varicocele and a scrotal vein with a diameter of > or = 3 mm on color Doppler ultrasonography were included in the study. A total of 44 fertile normal male volunteers served as controls.

RESULTS

Median testicular arterial blood flow and median flow rate in milliliters per minute per 100 g of testicular tissue were found to be significantly decreased in the patient group compared to the control group: blood flow, 1.42 and 2.00 ml/min; flow rate, 9.63 and 12.35 ml/min/100 g, respectively (p < 0.05). Positive correlations were found between sperm concentration and left testicular artery blood flow (p < 0.05) and between left testicular volume and testicular artery blood flow (p < 0.05).

CONCLUSIONS

Testicular arterial blood flow was found to be significantly decreased in men with varicocele. This may be a reflection of the impaired microcirculation. Following decreased testicular arterial blood flow, impaired spermatogenesis may result from defective energy metabolism in the microcirculatory bed.

Evidence for production and functional activity of nitric oxide in seminiferous tubules and blood vessels of the human testis

Previous studies have demonstrated that nitric oxide (NO) influences Leydig cell function. Here we provide evidence for NO production and activity in seminiferous tubules and blood vessels of the human testis. By immunohistochemistry, the soluble guanylyl cyclase (sGC), the intracellular NO receptor, and the second messenger, cyclic guanosine monophosphate (cGMP), were detected in myofibroblasts of the peritubular lamina propria in Sertoli cells, as well as in endothelial and smooth muscle cells of testicular blood vessels. Performed with isolated tubules and blood vessels, the biological activity of sGC could be proved by cGMP generation in response to treatments with the NO donor, sodium nitroprusside. The endothelial and neuronal subtypes of NO synthase (NOS) were localized immunohistochemically to the same cell types that express sGC and cGMP. In isolated tubules and vessels, the presence of endothelial NOS and neuronal NOS was confirmed by immunoblotting, and NOS activity was demonstrated by decreased cGMP production upon incubation with the NOS inhibitor L-nitro arginine methylester. These findings show that peritubular cells, Sertoli cells, and testicular blood vessels may be sites of NO production and activity, possibly involved in relaxation of seminiferous tubules and blood vessels to modulate sperm transport and testicular blood flow, respectively.

New aspects of Leydig cell function

Previous studies indicated that the Leydig cells of the human testes show similarities to neuroendocrine cells. In this context, the local synthesis of two neuroactive signaling molecules, namely nitric oxide (NO) and C-type natriuretic peptide (CNP), both acting via the second messenger, cyclic guanosine monophosphate (cGMP), might be of physiological relevance. By immunoblotting, immunohistochemical analyses and affinity crosslinking experiments, respectively, the presence of soluble guanylate cyclase (sGC), the NO receptor, and of guanylate cyclase B (GC-B), representing the CNP receptor, was demonstrated in Leydig cells, seminiferous tubules and blood vessels of the human testis. Moreover, cGMP and its binding protein cGMP-dependent protein kinase type I (GK I) were found in these structures. The functional activity of the two receptors was proved by generation of cGMP in response to treatments with the NO donor, sodium nitroprusside (SNP), and with CNP, respectively. As indicated by immunohistochemical analyses and by treatments of cells with either SNP or CNP, human Leydig tumour cells and MA10 cells, representing a mouse Leydig tumour cell line, were found to be distinguished by a reduced expression of the receptors for NO and CNP. Furthermore, expression levels of the components of the two cGMP-generating systems were found to be widely unchanged in Leydig cells during different ontogenetic stages. Though cGMP has been shown to influence testosterone release, the constant developmental expression patterns of NO and CNP apparently independent of differences in androgen production, the down-regulation of their receptors in tumorous cells, and the presence of GK I, may point to additional autocrine functions of these factors and of cGMP in Leydig cells. Moreover, possible paracrine actions of NO and CNP may include relaxation of seminiferous tubules and blood vessels in order to modulate sperm transport and testicular blood flow, respectively. These findings suggest that Leydig cell-derived factors may exert activities different from or in addition to those involved in the regulation of testosterone production.