Expression, activity, and subcellular localization of testicular hormone-sensitive lipase during postnatal development in the guinea pig

PCSK9 Contributes to the Cholesterol, Glucose, and Insulin2 Homeostasis in Seminiferous Tubules and Maintenance of Immunotolerance in Testis

The PCSK9 contribution to cholesterol and immunotolerance homeostasis and response to glucose, and insulin in testis and hypophysis were studied using Pcsk9-deficient (-/-) and transgenic [Tg (PCSK9)] mice, and diabetic, obese ob/ob and db/db mice. The spermatids/spermatozoa acrosome, peritubular vessels, and epididymal adipocytes were PCSK9- and LDL-R-positive. The pro-PCSK9/PCSK9 ratio was high in interstitial tissue-fractions (ITf) and spermatozoa and low in seminiferous tubule-fractions (STf) in normal adult mice. This ratio decreased in ITf in ob/ob and db/db mice but increased in tubules in ob/ob mice. Deleting pcsk9 lowered cholesterol in serum but increased testicular cholesterol. Furthermore, HMGCoA-red, ACAT-2 and LDL-R turnover increased whereas SR-BI decreased in ITf; in tubules, ABCA1 decreased and 160 kDa LDL-R increased in Pcsk9 -/- mice. Excess testicular cholesterol could result from increased cholesterol synthesis and uptake with reduction in SR-BI-mediated efflux in ITf and from the overload of apoptotic cells, lowered ABCA1-mediated efflux and stimulated LDL-R protein synthesis in tubules in Pcsk9 -/- mice. Concomitantly with the cholesterol accumulation, tubules showed infiltrates of immune cells, elevated IL-17A and IL-17RA, and changes in the immunotolerance homeostasis. PCSK9 deficiency decreased glucose in tubules and spermatozoa while increasing insulin2 in ITf and tubules not serum. Moreover, IR-α, and IR-β augmented in tubules but decreased in the anterior pituitary; IR-α increased whereas IR-β decreased in ITf. The histology and cholesterol levels were normal in Tg (PCSK9) mouse testis. The excess cholesterol creates a milieu favorable to the action of high IL-17A and IL-17RA, the development of inflammatory conditions and self-tolerance breakdown in testis.

Hormone-sensitive lipase: sixty years later

Hormone-sensitive lipase (HSL) was initially characterized as the hormonally regulated neutral lipase activity responsible for the breakdown of triacylglycerols into fatty acids in adipose tissue. This review aims at providing up-to-date information on structural properties, regulation of expression, activity and function as well as therapeutic potential. The lipase is expressed as different isoforms produced from tissue-specific alternative promoters. All isoforms are composed of an N-terminal domain and a C-terminal catalytic domain within which a regulatory domain containing the phosphorylation sites is embedded. Some isoforms possess additional N-terminal regions. The catalytic domain shares similarities with bacteria, fungus and vascular plant proteins but not with other mammalian lipases. HSL singularity is provided by regulatory and N-terminal domains sharing no homology with other proteins. HSL has a broad substrate specificity compared to other neutral lipases. It hydrolyzes acylglycerols, cholesteryl and retinyl esters among other substrates. A novel role of HSL, independent of its enzymatic function, has recently been described in adipocytes. Clinical studies revealed dysregulations of HSL expression and activity in disorders, such as lipodystrophy, obesity, type 2 diabetes and cancer-associated cachexia. Development of specific inhibitors positions HSL as a pharmacological target for the treatment of metabolic complications.

FXRα modulates leydig cell endocrine function in mouse

The hypothalamic-pituitary axis exert a major control over endocrine and exocrine testicular functions. The hypothalamic-pituitary axis corresponds to a cascade with the Gonadotropin Releasing Hormone secreted by the hypothalamus, which stimulates the synthesis and the release of Luteinizing Hormone (LH) and Follicle Stimulating Hormone by the gonadotropic cells of the anterior pituitary. The LH signaling pathway controls the steroidogenic activity of the Leydig cells via the activation of the luteinizing hormone/choriogonadotropin receptor. In order to avoid a runaway system, sex steroids exert a negative feedback within hypothalamus and pituitary. Testicular steroidogenesis is locally controlled within Leydig cells. The present work reviews some local regulations of steroidogenesis within the Leydig cells focusing mainly on the roles of the Farnesoid-X-Receptor-alpha and its interactions with several orphan members of the nuclear receptor superfamily. Further studies are required to reinforce our knowledge of the regulation of testicular endocrine function, which is necessary to ensure a better understanding of fertility disorders and then proposed an adequate treatment of the diseases.

Cholesterol: A Gatekeeper of Male Fertility?

Cholesterol is essential for mammalian cell functions and integrity. It is an important structural component maintaining the permeability and fluidity of the cell membrane. The balance between synthesis and catabolism of cholesterol should be tightly regulated to ensure normal cellular processes. Male reproductive function has been demonstrated to be dependent on cholesterol homeostasis. Here we review data highlighting the impacts of cholesterol homeostasis on male fertility and the molecular mechanisms implicated through the signaling pathways of some nuclear receptors.

Cholesterol metabolism and Cx43, Cx46, and Cx50 gap junction protein expression and localization in normal and diabetic and obese ob/ob and db/db mouse testes

Decreased fertility and birth rates arise from metabolic disorders. This study assesses cholesterol metabolism and Cx46, Cx50, and Cx43 expression in interstitium- and seminiferous tubule-enriched fractions of leptin-deficient ( ob/ob) and leptin receptor-deficient ( db/db) mice, two type 2 diabetes and obesity models associated with infertility. Testosterone levels decreased and glucose and free and esterified cholesterol (FC and EC) levels increased in serum, whereas FC and EC levels decreased in the interstitium, in ob/ob and db/db mice. In tubules, a decrease in EC caused FC-to-EC ratios to increase in db/db mice. In tubules, only acyl coenzyme A:cholesterol acyl transferase type 1 and 2 protein levels significantly decreased in ob/ob, but not db/db, mice compared with wild-type mice, and imbalances in the cholesterol transporters Niemann-Pick C1 (NPC1), ATP-binding cassette A1 (ABCA1), scavenger receptor class B member I (SR-BI), and cluster of differentiation 36 (CD36) were observed in ob/ob and db/db mice. In tubules, 14-kDa Cx46 prevailed during development, 48- to 49- and 68- to 71-kDa Cx46 prevailed during adulthood, and total Cx46 changed little. Compared with wild-type mice, 14-kDa Cx46 increased, whereas 48- to 49- and 68- to 71-kDa Cx46 decreased, in tubules, whereas the opposite occurred in the interstitium, in db/db and ob/ob mice. Total and 51-kDa Cx50 increased in db/db and ob/ob interstitium and tubules. Cx43 levels decreased in ob/ob interstitium and tubules, whereas Cx43 decreased in db/db interstitium but increased in db/db tubules. Apoptosis levels measured by ELISA and numbers of apostain-labeled apoptotic cells significantly increased in db/db, but not ob/ob, tubules. Testicular db/db capillaries were Cx50-positive but weakly Cx43-positive with a thickened lamina, suggesting altered permeability. Our findings indicate that the db mutation-induced impairment of meiosis may arise from imbalances in cholesterol metabolism and upregulated Cx43 expression and phosphorylation in tubules.

Complementary expression and phosphorylation of Cx46 and Cx50 during development and following gene deletion in mouse and in normal and orchitic mink testes

Gap junction-mediated communication helps synchronize interconnected Sertoli cell activities. Besides, coordination of germ cell and Sertoli cell activities depends on gap junction-mediated Sertoli cell-germ cell communication. This report assesses mechanisms underlying the regulation of connexin 46 (Cx46) and Cx50 in mouse testis and those accompanying a "natural" seasonal and a pathological arrest of spermatogenesis, resulting from autoimmune orchitis (AIO) in mink. Furthermore, the impact of deleting Cx46 or Cx50 on the expression, phosphorylation of junction proteins, and spermatogenesis is evaluated. Cx46 mRNA and protein expression increased, whereas Cx50 decreased with adulthood in normal mice and mink. Cx46 mRNA and protein expression increased, whereas Cx50 decreased with adulthood in normal mice and mink. During the mink active spermatogenic phase, Cx50 became phosphorylated and localized to the site of the blood-testis barrier. By contrast, Cx46 was dephosphorylated and associated with annular junctions, suggesting phosphorylation/dephosphorylation of Cx46 and Cx50 involvement in the barrier dynamics. Cx46-positive annular junctions in contact with lipid droplets were found. Cx46 and Cx50 expression and localization were altered in mink with AIO. The deletion of Cx46 or Cx50 impacted on other connexin expression and phosphorylation and differently affected tight and adhering junction protein expression. The level of apoptosis, determined by ELISA, and a number of Apostain-labeled spermatocytes and spermatids/tubules were higher in mice lacking Cx46 (Cx46-/-) than wild-type and Cx50-/- mice, arguing for life-sustaining Cx46 gap junction-mediated exchanges in late-stage germ cells secluded from the blood by the barrier. The data show that expression and phosphorylation of Cx46 and Cx50 are complementary in seminiferous tubules.

HSL-knockout mouse testis exhibits class B scavenger receptor upregulation and disrupted lipid raft microdomains

There is a tight relationship between fertility and changes in cholesterol metabolism during spermatogenesis. In the testis, class B scavenger receptors (SR-B) SR-BI, SR-BII, and LIMP II mediate the selective uptake of cholesterol esters from HDL, which are hydrolyzed to unesterified cholesterol by hormone-sensitive lipase (HSL). HSL is critical because HSL knockout (KO) male mice are sterile. The aim of the present work was to determine the effects of the lack of HSL in testis on the expression of SR-B, lipid raft composition, and related cell signaling pathways. HSL-KO mouse testis presented altered spermatogenesis associated with decreased sperm counts, sperm motility, and infertility. In wild-type (WT) testis, HSL is expressed in elongated spermatids; SR-BI, in Leydig cells and spermatids; SR-BII, in spermatocytes and spermatids but not in Leydig cells; and LIMP II, in Sertoli and Leydig cells. HSL knockout male mice have increased expression of class B scavenger receptors, disrupted caveolin-1 localization in lipid raft plasma membrane microdomains, and activated phospho-ERK, phospho-AKT, and phospho-SRC in the testis, suggesting that class B scavenger receptors are involved in cholesterol ester uptake for steroidogenesis and spermatogenesis in the testis.

Arylsulfatase A deficiency causes seminolipid accumulation and a lysosomal storage disorder in Sertoli cells

Sulfogalactosylglycerolipid (SGG) is the major sulfoglycolipid of male germ cells. During spermatogenesis, apoptosis occurs in >50% of total germ cells. Sertoli cells phagocytose these apoptotic germ cells and degrade their components using lysosomal enzymes. Here we demonstrated that SGG was a physiological substrate of Sertoli lysosomal arylsulfatase A (ARSA). SGG accumulated in Sertoli cells of Arsa(-/-) mice, and at 8 months of age, this buildup led to lysosomal swelling and other cellular abnormalities typical of a lysosomal storage disorder. This disorder likely compromised Sertoli cell functions, manifesting as impaired spermatogenesis and production of sperm with near-zero fertilizing ability in vitro. Fecundity of Arsa(-/-) males was thus reduced when they were older than 5 months. Sperm SGG is known for its roles in fertilization. Therefore, the minimal sperm fertilizing ability of 8-month-old Arsa(-/-) males may be explained by the 50% reduction of their sperm SGG levels, a result that was also observed in testicular germ cells. These unexpected decreases in SGG levels might be partly due to depletion of the backbone lipid palmitylpalmitoylglycerol that is generated from the SGG degradation pathway in Sertoli cells and normally recycled to new generations of primary spermatocytes for SGG synthesis.

Genetic variation of hormone sensitive lipase and male infertility

Hormone sensitive lipase (HSL) is a triacylglycerol hydrolase and cholesterol esterase that is essential for male fertility. The aim of the study was to investigate the distribution of C-60G polymorphism of HSL gene and alleles in fertile and infertile males living in Hamadan, Iran. In addition, lipase activity was determined in these two groups. The HSL genotype was determined by PCR-RFLP and the lipase activity was detected by turbidometery in 164 fertile and 169 infertile males. A significant difference in HSL genotype distribution was observed between groups (χ2  =  8.1, df  =  2, p  =  0.017). Infertile males showed a higher percentage of CC as well as a lower percentage of CG and GG genotype compared with fertile individuals. The presence of CC to CG + GG genotype conferred a 2.4-fold risk for male infertility (odds ratio = 2.4 (1.3 - 4.5), p = 0.006). In addition, lipase activity was remarkably higher (p < 0.001) in fertile males (94  ±  66 U/L) compared to the infertile subjects (50.6  ±  49 U/L). This suggests that genetic variation of HSL may be a risk factor for male infertility.

The blood-testis barrier: the junctional permeability, the proteins and the lipids

The elucidation of how individual components of the Sertoli cell junctional complexes form and are dismantled to allow not only individual cells but whole syncytia of germinal cells to migrate from the basal to the lumenal compartment of the seminiferous epithelium without causing a permeability leak in the blood-testis barrier is amongst the most enigmatic yet, challenging and timely questions in testicular physiology. The intriguing key event in this process is how the barrier modulates its permeability during the periods of formation and dismantling of individual Sertoli cell junctions. The purpose of this review is therefore to first provide a reliable account on the normal formation, maintenance and dismantling process of the Sertoli cells junctions, then to assess the influence of the expression of their individual proteins, of the cytoskeleton associated with the junctions, and of the lipid content in the seminiferous tubules on the regulation of the their permeability barrier function. To help focus on the formation and dismantling of the Sertoli cell junctions, several considerations are based on data gleaned not only from rodents but from seasonal breeders as well because these animal models are characterized by exhaustive periods of junction assembly during development and the onset of the seasonal re-initiation of spermatogenesis as well as by an extensive junction dismantling period at the beginning of testicular regression, something unavailable in normal physiological conditions in continual breeders. Thus, the modulation of the permeability barrier function of the Sertoli cell junctions is analyzed in the physiological context of the blood-epidydimis barrier and in particular of the blood-testis barrier rather than in the context of a detailed account of the molecular composition and signalisation pathways of cell junctions. Moreover, the considerations discussed in this review are based on measurements performed on seminiferous tubule-enriched fractions gleaned at regular time intervals during development and the annual reproductive cycle.

CX43 expression, phosphorylation, and distribution in the normal and autoimmune orchitic testis with a look at gap junctions joining germ cell to germ cell

Spermatogenesis requires connexin 43 (Cx43).This study examines normal gene transcription, translation, and phosphorylation of Cx43 to define its role on germ cell growth and Sertoli cell's differentiation, and identifies abnormalities arising from spontaneous autoimmune orchitis (AIO) in mink, a seasonal breeder and a natural model for autoimmunity. Northern blot analysis detected 2.8- and a 3.7-kb Cx43 mRNA bands in seminiferous tubule-enriched fractions. Cx43 mRNA increased in seminiferous tubule-enriched fractions throughout development and then seasonally with the completion of spermatogenesis. Cx43 protein levels increased transiently during the colonization of the tubules by the early-stage spermatocytes. Cx43 phosphorylated (PCx43) and nonphosphorylated (NPCx43) in Ser368 decreased during the periods of completion of meiosis and Sertoli cell differentiation, while Cx43 mRNA remained elevated throughout. PCx43 labeled chiefly the plasma membrane except by stage VII when vesicles were also labeled in Sertoli cells. Vesicles and lysosomes in Sertoli cells and the Golgi apparatus in the round spermatids were NPCx43 positive. A decrease in Cx43 gene expression was matched by a Cx43 protein increase in the early, not the late, phase of AIO. Total Cx43 and PCx43 decreased with the advance of orchitis. The study makes a novel finding of gap junctions connecting germ cells. The data indicate that Cx43 protein expression and phosphorylation in Ser368 are stage-specific events that may locally influence the acquisition of meiotic competence and the Sertoli cell differentiation in normal testis. AIO modifies Cx43 levels, suggesting changes in Cx43-mediated intercommunication and spermatogenic activity in response to cytokines imbalances in Sertoli cells.

Differentiation-related changes in lipid classes with long-chain and very long-chain polyenoic fatty acids in rat spermatogenic cells

In rat seminiferous tubules (ST), cells that contain polar and neutral lipids with long-chain polyenoic fatty acids (PUFA) and sphingomyelins (SM) and ceramides (Cer) with very long chain (VLC) PUFA of the n-6 series coexist. In this study, pachytene spermatocytes and round spermatids were isolated to determine how these lipids change during spermatogenesis. As the amount per cell of PUFA-rich glycerophospholipids (GPL) decreased with cell size, the 22:5/20:4 ratio increased with cell differentiation. The elovl2 and elovl5 genes, required for 22:5 formation, were expressed (mRNA) in both cell types. Residual bodies- particles with compacted organelles and materials discarded from late spermatids-concentrated cholesterol, 22:5-rich triacylglycerols, and GPL, including plasmalogens and phosphatidylserine. Species of SM and Cer with nonhydroxylated (n-) VLCPUFA (28:4, 30:5, and 32:5) predominated in pachytene spermatocytes, whereas species with the corresponding 2-hydroxy (2-OH) VLCPUFA prevailed in round spermatids. Thus, a dramatic increase in the 2-OH/n-VLCPUFA ratio in SM and Cer was a hallmark of differentiation. A substantial decrease of 2-OH SM occurred between spermatids and mature spermatozoa and 2-OH SM species were collected in residual bodies "en route" to Sertoli cells. Notably, spermatids and spermatozoa gained a significant amount of ceramides devoid of n-VLCPUFA but having 2-OH VLCPUFA as their main fatty acids.

Surfing the wave, cycle, life history, and genes/proteins expressed by testicular germ cells. Part 5: intercellular junctions and contacts between germs cells and Sertoli cells and their regulatory interactions, testicular cholesterol, and genes/proteins associated with more than one germ cell generation

In the testis, cell adhesion and junctional molecules permit specific interactions and intracellular communication between germ and Sertoli cells and apposed Sertoli cells. Among the many adhesion family of proteins, NCAM, nectin and nectin-like, catenins, and cadherens will be discussed, along with gap junctions between germ and Sertoli cells and the many members of the connexin family. The blood-testis barrier separates the haploid spermatids from blood borne elements. In the barrier, the intercellular junctions consist of many proteins such as occludin, tricellulin, and claudins. Changes in the expression of cell adhesion molecules are also an essential part of the mechanism that allows germ cells to move from the basal compartment of the seminiferous tubule to the adluminal compartment thus crossing the blood-testis barrier and well-defined proteins have been shown to assist in this process. Several structural components show interactions between germ cells to Sertoli cells such as the ectoplasmic specialization which are more closely related to Sertoli cells and tubulobulbar complexes that are processes of elongating spermatids embedded into Sertoli cells. Germ cells also modify several Sertoli functions and this also appears to be the case for residual bodies. Cholesterol plays a significant role during spermatogenesis and is essential for germ cell development. Lastly, we list genes/proteins that are expressed not only in any one specific generation of germ cells but across more than one generation.

Cortactin/tyrosine-phosphorylated cortactin interaction with connexin 43 in mouse seminiferous tubules

Deletion of the cortactin gene leads to male infertility. Considering that cortactin is an actin filament (F-actin)-binding protein associated with intercellular junctions, we measured changes in the expression and distribution of cortactin and tyrosine phosphorylated cortactin (P-cortactin) in the seminiferous epithelium of developing and adult mice to address the physiological significance of cortactin to germ cell differentiation. Cortactin was expressed in neonatal and developing Sertoli cells. Cortactin levels decreased early during puberty, while P-cortactin increased. Cortactin labeling was intense in the basal and apical thirds of the epithelium. Sertoli cell cytoplasmic processes facing spermatogonia, preleptotene spermatocytes, and step 8-13 spermatids were intensely labeled by both cortactin and P-cortactin. In contrast, the middle region of Sertoli cells exhibited diffuse cortactin labeling but no P-cortactin. This is consistent with the view that plasma membrane segments facing germ cells are part of the continuum of Sertoli cell junctional complexes that extend over lateral and apical membranes of supporting cells. Moreover, F-actin and P-cortactin share a common location in the seminiferous epithelium. The increased P-cortactin levels detected during puberty may be related to the modulatory effect of cortactin tyrosine phosphorylation on actin assembly at sites of selected Sertoli cell-germ cell contacts. Cortactin and connexin 43 (Cx43) were physically linked in seminiferous tubule homogenates and their colocalization in the basal and apical thirds of the seminiferous epithelium was stage-dependent. Our results suggest that cortactin-Cx43 interaction helps coordinate formation of cell-to-cell junctions and organization of the subsurface actin cytoskeleton in specific regions of the epithelium.

A revised and improved method for the isolation of seminiferous tubule-enriched fractions that preserves the phosphorylated and glycosylated forms of proteins

An improved technique to generate high yields of relatively pure seminiferous tubule-enriched fractions from mouse testis by manual isolation is described. Our laboratory had previously developed an isolation method based on mild enzymatic digestion to separate individual constituents of each compartment of the testis, namely, the interstitial tissue and the seminiferous tubules. Although the method had the advantage of allowing the production of seminiferous tubule-enriched fractions in large amounts, we show here that this approach does not allow optimal preservation of the integrity of the proteins in the samples, in particular of the phosphorylated and/or glycosylated forms of the proteins. In an attempt to solve this problem, we developed a novel mechanical approach to generate interstitial tissue- and seminiferous tubule-enriched fractions that does not require the use of enzymatic digestion. This approach has the advantages of providing relatively pure seminiferous tubule-enriched fractions in large quantities and in a short amount of time. In addition, and more significantly, the approach allows a more faithful detection of the phosphorylated and glycosylated forms of the proteins.

Defects in the regulatory clearance mechanisms favor the breakdown of self-tolerance during spontaneous autoimmune orchitis

We identified aberrations leading to spontaneous autoimmune orchitis (AIO) in mink, a seasonal breeder and natural model for autoimmunity. This study provides evidence favoring the view that a malfunction of the clearance mechanisms for apoptotic cell debris arising from imbalances in phagocyte receptors or cytokines acting on Sertoli cells constitutes a major factor leading to breakdown of self-tolerance during spontaneous AIO. Serum anti-sperm antibody titers measured by ELISA reflected spermatogenic activity without causing immune inflammatory responses. Orchitic mink showed excess antibody production accompanied by spermatogenic arrest, testicular leukocyte infiltration, and infertility. AIO serum labeled the postacrosomal region, the mid and end piece of mink sperm, whereas normal mink serum did not. Normal serum labeled plasma membranes, whereas AIO serum reacted with germ cell nuclei. Western blot analyses revealed that AIO serum reacted specifically to a 23- and 50-kDa protein. The number of apostain-labeled apoptotic cells was significantly higher in orchitic compared with normal tubules. However, apoptosis levels measured by ELISA in seminiferous tubular fractions (STf) were not significantly different in normal and orchitic tubules. The levels of CD36, TNF-alpha, TNF-alpha RI, IL-6, and Fas but not Fas-ligand (L), and ATP-binding cassette transporter ABCA1 were changed in AIO STf. TNF-alpha and IL-6 serum levels were increased during AIO. Fas localized to germ cells, Sertoli cells, and the lamina propria of the tubules and Fas-L, to germ cells. Fas colocalized with Fas-L in residual bodies in normal testis and in giant cells and infiltrating leukocytes in orchitic tubules.

Mono-(2-ethylhexyl) phthalate stimulates basal steroidogenesis by a cAMP-independent mechanism in mouse gonadal cells of both sexes

Phthalates are widely used as plasticizers in a number of daily-life products. In this study, we investigated the influence of mono-(2-ethylhexyl) phthalate (MEHP), the active metabolite of the frequently used plasticizer di-(2-ethylhexyl) phthalate (DEHP), on gonadal steroidogenesisin vitro. MEHP (25–100 μM) stimulated basal steroid synthesis in a concentration-dependent manner in immortalized mouse Leydig tumor cells (MLTC-1). The stimulatory effect was also detected in KK-1 granulosa tumor cells. MEHP exposure did not influence cAMP or StAR protein levels and induced a gene expression profile of key steroidogenic proteins different from the one induced by human chorionic gonadotropin (hCG). Simultaneous treatment with MEHP and a p450scc inhibitor (aminoglutethimide) indicated that MEHP exerts its main stimulatory effect prior to pregnenolone formation. MEHP (10–100 μM) up-regulated hormone-sensitive lipase and 3-hydroxy-3-methylglutaryl coenzyme A reductase, suggesting that MEHP increases the amount of cholesterol available for steroidogenesis. Our data suggest that MEHP, besides its known inhibitory effect on hCG action, can directly stimulate gonadal steroidogenesis in both sexes through a cAMP- and StAR-independent mechanism. The anti-steroidogenic effect of DEHP has been proposed to cause developmental disorders such as hypospadias and cryptorchidism, whereas a stimulation of steroid synthesis may prematurely initiate the onset of puberty and theoretically affect the hypothalamic–pituitary–gonadal axis.

The predominance of one of the SR-BI isoforms is associated with increased esterified cholesterol levels not apoptosis in mink testis

Scavenger receptor class B type I (SR-BI) contributes to HDL-mediated cellular cholesterol efflux and is a phagocytosis-inducing phospholipid phosphatidylserine receptor in rat Sertoli cells, whereas the spliced variant of the SR-B gene, SR-BII, is implicated in the efflux of free cholesterol in macrophages. This study aimed to assess whether spontaneous autoimmune orchitis (AIO), which causes impaired clearance of apoptotic germ cells and spermatogenic arrest, involves SR-BI, SR-BII, and/or cholesterol. The levels measured during development and the annual reproductive cycle in normal mink were compared with those in mink with spontaneous AIO. Time periods with lowest tubular esterified cholesterol (EC) levels showed maximal SR-BI and SR-BII levels, and the periods when one or the other SR-BI isoform predominated showed increased EC levels and spermatogenic arrest in normal mink seminiferous tubules. In tubules with AIO, the predominance of only one or the other SR-BI isoform was the reverse of that measured in normal tubules, and it was associated with an increase in EC levels but not with apoptosis levels. SR-BI and SR-BII levels were not correlated with serum testosterone levels. SR-BI mainly localized to the Leydig cell, germ cell, and Sertoli cell surface, where its distribution was stage-specific. SR-BII was principally intracellular. Tubules from testes with AIO showed a deregulation of cholesterol homeostasis and SR-BI expression but relatively unchanged apoptosis levels. These results suggest that the expression of both SR-BI isoforms is required for the maintenance of low EC levels and that the predominance of only one isoform is associated with the accumulation of EC but not with apoptosis in the tubules.

Sperm from Mice Genetically Deficient for the PCSK4 Proteinase Exhibit Accelerated Capacitation, Precocious Acrosome Reaction, Reduced Binding to Egg Zona Pellucida, and Impaired Fertilizing Ability1

The gene for proprotein convertase subtilisin/kexin-like 4 (PCSK4, previously known as PC4) is primarily transcribed in testicular spermatogenic cells. Its inactivation in mouse causes severe male subfertility. To better understand the reproductive function of PCSK4, we examined its subcellular localization in the testicular epithelium via immunohistochemistry, and on intact sperm via indirect immunofluorescence and immunoelectron microscopy. PCSK4 was detected in the acrosomal granules of round spermatids, in the acrosomal ridges of elongated spermatids, and on the sperm plasma membrane overlying the acrosome. We also investigated PCSK4 relevance for sperm acquisition of fertilizing ability by comparing wild-type and PCSK4-null sperm for their abilities in capacitation, acrosome reaction, and egg binding in vitro. PCSK4-null sperm underwent capacitation at a faster rate; they were induced to acrosome react by lower concentrations of zona pellucida; and their egg-binding ability was only half that of wild-type sperm. These sperm physiologic anomalies likely contribute to the severe subfertility of PCSK4-deficient male mice.

Expression of human hormone-sensitive lipase (HSL) in postmeiotic germ cells confers normal fertility to HSL-deficient mice

Hormone-sensitive lipase (HSL, Lipe, E.C.3.1.1.3) is a multifunctional fatty acyl esterase that is essential for male fertility and spermatogenesis and that also plays important roles in the function of adipocytes, pancreatic beta-cells, and adrenal cortical cells. Gene-targeted HSL-deficient (HSL-/-) male mice are infertile, have a 2-fold reduction in testicular mass, a 2-fold elevation of the ratio of esterified to free cholesterol in testis, and unique morphological abnormalities in round and elongating spermatids. Postmeiotic germ cells in the testis express a specific HSL isoform. We created transgenic mice expressing a normal human testicular HSL cDNA from the mouse protamine-1 promoter, which mediates expression specifically in postmeiotic germ cells. Testicular cholesteryl esterase activity was undetectable in HSL-/- mice, but in HSL-/- males expressing the testicular transgene, activity was 2-fold greater than normal. HSL transgene mRNA became detectable in testes between 19 and 25 days of age, coinciding with the first wave of postmeiotic transcription in round spermatids. In contrast to nontransgenic HSL-/- mice, HSL-/- males expressing the testicular transgene were normal with respect to fertility, testicular mass, testicular esterified/free cholesterol ratio, and testicular histology. Their cauda epididymides contained abundant, normal-appearing spermatozoa. We conclude that human testicular HSL is functional in mouse testis and that the mechanism of infertility in HSL-deficient males is cell autonomous and resides in postmeiotic germ cells, because HSL expression in these cells is in itself sufficient to restore normal fertility.

The Testicular Form of Hormone-sensitive Lipase HSLtes Confers Rescue of Male Infertility in HSL-deficient Mice

Inactivation of the hormone-sensitive lipase gene (HSL) confers male sterility with a major defect in spermatogenesis. Several forms of HSL are expressed in testis. HSLtes mRNA and protein are found in early and elongated spermatids, respectively. The other forms are expressed in diploid germ cells and interstitial cells of the testis. To determine whether the absence of the testis-specific form of HSL, HSLtes, was responsible for the infertility in HSL-null mice, we generated transgenic mice expressing HSLtes under the control of its own promoter. The transgenic animals were crossed with HSL-null mice to produce mice deficient in HSL in nongonadal tissues but expressing HSLtes in haploid germ cells. Cholesteryl ester hydrolase activity was almost completely blunted in HSL-deficient testis. Mice with one allele of the transgene showed an increase in enzymatic activity and a small elevation in the production of spermatozoa. The few fertile hemizygous male mice produced litters of very small to small size. The presence of the two alleles led to a doubling in cholesteryl ester hydrolase activity, which represented 25% of the wild type values associated with a qualitatively normal spermatogenesis and a partial restoration of sperm reserves. The fertility of these mice was totally restored with normal litter sizes. In line with the importance of the esterase activity, HSLtes transgene expression reversed the cholesteryl ester accumulation observed in HSL-null mice. Therefore, expression of HSLtes and cognate cholesteryl ester hydrolase activity leads to a rescue of the infertility observed in HSL-deficient male mice.

Normal and pathological human testes express hormone-sensitive lipase and the lipid receptors CLA-1/SR-BI and CD36

Numerous studies have demonstrated the important role of cholesterol and cholesteryl esters in tumor cell proliferation and progression of cancer. However, few studies have focused on the role of lipid transporters and lipases in cancer development and progression. The present study examined the expression of hormone-sensitive lipase (HSL) and the scavenger receptors CLA-1/SR-BI and CD36 in normal human testis and in nontumor and tumor testicular disorders by immunohistochemistry and Western blotting analysis. In normal young testes, immunoreaction to CLA-1/SR-BI was found in the spermatid acrosomic vesicle and on the surface of Sertoli and Leydig cells. HSL was detected in spermatogonia, the Golgi region of spermatocytes, the nucleus of spermatids, and the cytoplasm of both Sertoli and Leydig cells. Elderly testes and testes with hypospermatogenesis showed a similar staining pattern to that of normal young testes except for CD36, which was expressed in Sertoli cells. Cryptorchid testes demonstrated intense labeling to HSL and weak labeling to SR-BI in Sertoli cells (nucleus and cytoplasm) and Leydig cells (cytoplasm). Seminiferous tubules with intratubular germ cell neoplasia exhibited intense immunolabeling to the 3 lipid receptors in the surface of neoplastic cells and to HSL in the nucleus. In seminoma and spermatocytic seminoma, neoplastic cells labeled to HSL but failed to stain with antilipid receptors; in the seminiferous tubules at the periphery of the tumour, Charcot-Böttcher crystalloids of Sertoli cells were strongly positive to CLA-1. Testes with mature teratoma showed a weak reaction to CD36 and SR-BI in some cells of enteric-type glands, and immature teratoma were exclusively immunolabeled with HSL. Western blotting analysis revealed that multiple bands were immunolabeled, with differences seen between normal and pathological testes. The results of this study indicate that the presence of lipid receptors (CLA-1/SR-BI) and hormone-sensitive lipase in Leydig cells suggests a role of these proteins in steroidogenesis. Also, these proteins seem to be involved in spermiogenesis, as their labeling in spermatids suggests. In nonmalignant and malignant pathologies, cholesterol metabolism is probably altered, and HSL labeling in neoplastic germ cell nuclei suggests a still-unknown function of this enzyme, probably related to cell cycle regulation.

Androgens up-regulate atherosclerosis-related genes in macrophages from males but not females: molecular insights into gender differences in atherosclerosis

OBJECTIVES

This study investigated the effects of androgens on gene expression in male- and female-donor macrophages.

BACKGROUND

Men have more severe coronary disease than women. Androgen exposure increases foam cell formation in male but not female macrophages, and male macrophages express >4-fold more androgen receptor messenger ribonucleic acid than female macrophages. Therefore, androgen exposure may have gender-specific and potentially pro-atherogenic effects in macrophages.

METHODS

Utilizing complementary deoxyribonucleic acid arrays, we studied the effects of a pure androgen (dihydrotestosterone, 40 nmol/l) on human monocyte-derived macrophages from healthy male and female donors (n = 4 hybridizations; 2 men, 2 women). Differential expression of atherosclerosis-related genes was confirmed by real-time reverse transcription-polymerase chain reaction (RT-PCR) in five male and five female donors. Functional corroboration of foam cell formation-related findings was undertaken by experiments using (125)I-acetylated low-density lipoprotein (AcLDL).

RESULTS

In male macrophages, androgen treatment produced differential up-regulation of 27 genes concentrated in five functional classes: 1) lipoprotein processing; 2) cell-surface adhesion; 3) extracellular signaling; 4) coagulation and fibrinolysis; and 5) transport protein genes. By contrast, none of 588 genes were up-regulated in female macrophages. By RT-PCR, we confirmed the gender-specific up-regulation of six of these atherosclerosis-related genes: acyl coenzyme A:cholesterol acyl transferase I, lysosomal acid lipase (LAL), caveolin-2, CD40, vascular endothelial growth factor-165 receptor, and tissue factor pathway inhibitor. Functionally, androgen-treated male macrophages showed increased rates of lysosomal AcLDL degradation, by 45% to 75% after 15 to 20 h of (125)I-AcLDL incubation (p = 0.001), consistent with increased LAL activity.

CONCLUSIONS

Androgens increase expression of atherosclerosis-related genes in male but not female macrophages, with functional consequences. These findings may contribute to the male predisposition to atherosclerosis.

Relationship of the hormone-sensitive lipase-mediated modulation of cholesterol metabolism in individual compartments of the testis to serum pituitary hormone and testosterone concentrations in a seasonal breeder, the mink (Mustela vison)

The role of cholesterol differs in the two compartments of the testis. In the interstitial tissue, cholesterol is necessary for the synthesis of testosterone, whereas in the seminiferous tubules, membrane cholesterol content in developing germ cells will influence the gametes' fertility. Here we evaluate the hormone-sensitive lipase (HSL) modulation of the cholesterol metabolism in each compartment of the testis. Two HSL immunoreactive bands of 104- and 108-kDa were detected in Western blots performed with polyclonal anti-human HSL antibodies in the interstitial tissue (ITf)- and seminiferous tubule (STf)-enriched fractions generated from testes harvested at 30-day intervals during puberty and, in the adult mink, during the annual seasonal reproductive cycle. Epididymal spermatozoa expressed a 104-kDa HSL isoform, and HSL was active in these cells. Immunolabeling localized HSL to interstitial macrophages; Sertoli cells, where its distribution was stage specific; spermatids; and the equatorial segment of spermatozoa. Total HSL protein levels, specific enzymatic activity, and free cholesterol (FC):esterified cholesterol (EC) ratios varied concomitantly in STf and ITf and reached maximal values in the adult during the period of maximal spermatogenic activity. In STf, HSL-specific activity correlated with FC:EC ratios but not with triglyceride levels. In STf, high HSL-specific activity occurred concomitantly with high FSH serum levels. In ITf, HSL-specific activity was high during periods of low serum prolactin levels and high serum testosterone levels. The results suggest that 1) modulation of cholesterol metabolism in individual testicular compartments may be regulated by HSL isoforms expressed by distinct cells; 2) interstitial macrophages may be part of a system involved in the synthesis of steroid hormones and in the recycling of sterols in the interstitium, whereas in the tubules, recycling could be ensured by Sertoli cells; 3) there is distinctive substrate preference for testicular HSL; and 4) HSL may be the only cholesterol esterase in this location.

Hormone-sensitive lipase: control of intracellular tri-(di-)acylglycerol and cholesteryl ester hydrolysis

Hormone-sensitive lipase (HSL) is an intracellular neutral lipase that is capable of hydrolyzing triacylglycerols, diacylglycerols, monoacylglycerols, and cholesteryl esters, as well as other lipid and water soluble substrates. HSL activity is regulated post-translationally by phosphorylation and also by pretranslational mechanisms. The enzyme is highly expressed in adipose tissue and steroidogenic tissues, with lower amounts expressed in cardiac and skeletal muscle, macrophages, and islets. Studies of the structure of HSL have identified several amino acids and regions of the molecule that are critical for enzymatic activity and regulation of HSL. This has led to important insights into its function, including the interaction of HSL with other intracellular proteins, such as adipocyte lipid binding protein. Accumulating evidence has defined important functions for HSL in normal physiology, affecting adipocyte lipolysis, steroidogenesis, spermatogenesis, and perhaps insulin secretion and insulin action; however, direct links between abnormal expression or genetic variations of HSL and human disorders, such as obesity, insulin resistance, type 2 diabetes, and hyperlipidemia, await further clarification. The published reports examining the regulation, and function of HSL in normal physiology and disease are reviewed in this paper.

Characterization of a novel testicular form of human hormone-sensitive lipase

Hormone-sensitive lipase (HSL) is an esterase and lipase, which are essential for spermatogenesis. Two HSL mRNAs are expressed in human testis. A long form is encoded by a testis-specific exon and nine exons common to testis and adipocyte HSL. Here we show that the short-form 3.3-kb mRNA possesses a unique 5' end that is transcribed from a novel testis-specific exon. The corresponding protein is similar to the 775-amino-acid-long adipocyte HSL. Immunohistochemistry experiments on human testis sections revealed that the long form is strictly expressed in haploid germ cells whereas the short form is expressed in interstitial and tubular somatic cells as well as premeiotic germ cells.