To carry out a comprehensive search, the following databases were selected: MEDLINE, Scopus, Web of Science, LILACS, SciELO and Embase (via Portal de Periódicos CAPES, a Brazilian Institutional databay). Data collection was carried out for studies published until July 2021. The following keywords and Medical Subject Headings (MeSH) terms were used: (mucopolysaccharidosis OR sphingolipidosis OR glycogenosis OR glucoproteinosis OR “multiple sulphatase deficiency” OR lipidosis OR ″i cell disease” OR mucolipidosis OR gangliosidosis OR lipofuscinosis OR fucosidosis OR fabry OR gaucher OR “niemann pick” OR pompe OR “lysosomal storage”) AND (mice OR rat OR cat OR dog) AND (testis OR epididymis OR sperm OR spermatozoa OR semen OR acrosome OR gamete OR prostate OR “seminal vesicle” OR ovary OR uterus OR oocyte OR “pellucid zone” OR fertility OR sexual).

It was necessary to limit the search period to 2010 to 2021 in three databases: Web of Science, Scopus and Embase, due to the large number of results returned that would have made our search unfeasible. No initial time limit was used in the search of the other databases: MEDLINE, LILACS and SciELO.

We selected all abstracts according to the following inclusion criteria: 1. studies involving an animal model of LSD that mentioned or were directly focused on male or female reproductive parameters; 2. studies involving substrate storage in gonads that did not necessarily represent a specific LSD, but are lysosomal related disorders and would help in understanding the effects of such unsuitable accumulation in these tissues. 3. Studies directly focused on reproductive parameters of LSD models. All abstracts were analyzed independently by two of the authors and, in the case of any disagreement, the third author decided the inclusion or exclusion.

Some studies were focused on a broad characterization of knockout mice and mentioned the gonads as one of the objects of analysis. Seyrantepe et al. (2018) examined a model of Tay Sachs disease using a double mutant mouse (Hexa−/− and Neu3−/−), since it is known that sialidase (Neu3) is alternatively used to degrade the ganglioside GM2 in the absence of hexosaminidase A (Hex A). This ganglioside is known to be stored in neurons and macrophages, but testicular samples were analyzed by electron microscopy and Sertoli cells were found to be filled with lamellar bodies, suggesting lipidic storage in 4.5-month-old mice. Staropoli et al. (2012) detected numerous vacuoles in the epididymal cells in a mouse model of juvenile neuronal ceroid lipofuscinosis (JNCL). A Cln3 gene knock-out model was used, as mutations in this gene are the most frequent causes of JNCL. Cognitive impairments and vacuolated lymphocytes were expected, but after a broad phenotyping study, the epididymis was one of the organs with greater lipid storage.

Murray et al. (2007) evaluated a mouse model of Fabry disease, deficient in producing α-galactosidase A, a lysosomal enzyme that degrades glycosphingolipids, particularly globotriaosylceramide (Gb3). Mutant mice submitted to intravenous enzyme replacement therapy had their tissue evaluated using immunostaining. This showed that the enzymatic infusion had heterogenous systemic distribution, since the antibody was detected in the liver, kidneys, heart, adrenal gland, spleen, bone marrow and also in the testes.

A number of models of oligosaccharidosis presented signs of damage in reproductive tissues. Stinchi et al. (1999) generated a knockout model of α-mannosidosis, a lysosomal enzyme that degrades asparagine-linked carbohydrate cores of glycoproteins. Morphological signs of storage were found in the liver, kidneys, spleen, brain and testes. Similarly, Zhu et al. (2006) studied a knockout model of β-mannosidosis. The model failed to cleave a mannose sugar, present in oligosaccharides and glycoproteins. Among other findings, under optic and electronic microscopy the epididymis was seen to be filled with vacuoles.

Higuchi et al. (2012) evaluated a mouse model of mucopolysaccharidosis type II (MPS II) with animals submitted to intraventricular enzyme replacement therapy. The enzyme degrades glycosaminoglycans (GAGs) present in the intracellular and extracellular environment. Treated MPS II mice presented less storage in many tissues, including in the testes and ovaries. The authors had expected an increase in recombinant enzyme activity in a brain-specific manner; however, contrary to their expectations, the enzyme activity was also high in some peripheral tissues.

The biosynthesis, degradation and transport of lipids are extremely important to steroidogenesis (Xie et al., 2006). Steroid hormones, such as testosterone, progesterone and 17-β estradiol, use cholesterol as a precursor molecule. All these hormones control gametogenesis, estrous cycles, the maintenance of gonads, sexual behavior, parental care and the manifestation of male and female secondary sexual characters (Hull et al., 2007). For this reason, the worst morphological and physiological damage was present in models of lipidoses, sphingolipidoses or ceroid lipofuscinoses.

Sphingomyelinases degrade sphingomyelin into ceramide and phosphorylcholine. The pathophysiology in Niemann Pick disease is primarily due to the accumulation of sphingomyelin and other metabolically related lipids within the cells and tissues (Levade et al., 1999).

Butler et al. (2002) used a knockout model of Niemann-Pick A and B, an acid sphingomyelinase deficient mouse (ASM). Testicular sections of ASM deficient mice presented vacuoles and Sertoli cells full of vesicles with undigested material. Sperm presented changes in their plasma membrane, in acrosome reaction and failed in the mitochondrial membrane polarization. Morphological damage in the sperm head and flagellum were also noted, and the epididymal epithelia were filled with vacuoles. Despite all these structural problems, males were capable of mating but litter size and the number of litters were decreased compared to wild types. They also evaluated crossings with female mutants and litters were even more prejudiced, with a lower number of litters and litter sizes (Butler et al., 2002).

The same authors examined knockout and heterozygotes of the ASM model and detected two different sperm populations from Asm+/− (normal and affected sperm). They performed in vitro fertilization and could select normal sperm based on their morphology and on their mitochondrial membrane potential. The authors affirmed that sperm sorting offers several advantages over the existing assisted reproduction options for Niemann-Pick disease carrier couples and could have a major impact on the prevention of this, and perhaps other, genetic diseases (Butler et al., 2007).

Adamali et al. (1999a) studied the relevance of hexosaminidase (Hex) in the testes and epididymis. This lysosomal enzyme exists as two isoenzymes (Hex A, (subunit αβ and Hex B, subunit ββ) that degrade gangliosides (GM2), and both isoenzymes and GM2 are abundant in neurons and present in other visceral organs such as the liver and kidneys. The disruption of the Hexb gene, that encodes subunit β, impairs the activity of both Hex A and Hex B and mimics Sandhoff disease, a severe neurodegenerative LSD. In the testis, seminiferous tubules were similar to wild types, Sertoli and germ cells appeared normal, but myoid and interstitial macrophages showed an increased number of lysosomes. The epithelial cells of efferent ducts and epididymal ducts also had numerous lysosomes in 1-month-old affected male mice. The same group was examined in a Tay Sachs model (knockout for the subunit α, which disrupts only Hex A). In this model, the initial segments of the epididymal duct presented more evidence of lysosomal storage than the other segments (Adamali et al., 1999b). Both studies showed the importance of Hex in the biosynthesis and degradation of gangliosides in testicular and epididymal ducts.

Trasler et al. (1998) also used the mouse model of Sandhoff disease and found that testes weight, morphology and sperm count were unaffected in knockout mice. Epithelial cells of the epididymal and efferent ducts were affected by extensive lysosomal abnormalities. In contrast to the brain, where GM2 ganglioside accumulates, mutant mice accumulated two non-GM2 gangliosides in the epididymis. The mice were fertile, but their litter size was reduced after 9 weeks of the disease progression. The authors suggested that testes derived glycolipids could not be degraded and accumulated in lysosomes, leading to epididymal dysfunction and abnormalities in the epididymal luminal environment that supports sperm maturation.

Juneja. (2002) evaluated the fertility profile of male and female Hexb−/− mice. Males and females were fertile up to approximately 2.5-months-old and 2-months-old respectively. Knockout males presented a reduction to an absence in mating behavior from 84 to 94-days-old (almost 3-months of disease progression). Sperm from Hexb−/− showed lower in vitro fertilization. Three-month-old Hexb−/− females in contact with healthy males were unable to be impregnated, regardless of the presence of a vaginal plug. However, oocytes from Hexb−/− could be fertilized at a lower efficiency by spermatozoa from wild type mice. Hermo et al. (1997) detected a high expression of β-hexosaminidase in the epididymis and testes compared to other tissues and highlighted its relevance to the production and maturation of sperm.

Luddi et al. (2005) studied a male mouse model of globoid cell leukodystrophy (Krabbe disease), using mice with a mutation in the galactosylceramidase (GALC) gene. GALC hydrolyzes galactose from galactosylceramide, a typical component of the myelin membrane. The undigested substrate for GALC, galactosyl-alkyl-acyl-glycerol (GalAAG), accumulates in the testes and affects sperm number, maturation, morphology and function. The study proved that GALC plays a critical role in spermiogenesis. Another study using the same model confirmed the sperm and testicular morphological abnormalities and detected interference in the hypothalamus-pituitary-gonadal axis under RT PCR analysis, since LH and FSH were significantly decreased in mutant mice (Piomboni et al., 2014).

Wu et al. (2019) evaluated a model of metachromatic leukodystrophy that used arylsulfatase A (ARSA) knockout mice; ARSA catalyzes glycolipids of myelin. In this study, the researchers found that this enzyme is present in the acrosomal vesicle and reacts with cumulus oocyte complexes. Sperm from ARSA null mice showed a significant delay in the dispersion of cells present in cumulus oocyte complexes, which interfere in the efficiency of fertilization. The same model was used by Xu et al. (2011) who demonstrated that Sertoli cells depend on ARSA to degrade sulfogalactosylglycerolipid (SGG), the major sulfoglycolipid of sperm that is directly involved in the cell adhesion between testicular germ cells and Sertoli cells.

During spermatogenesis, approximately 50% of germ cells are sent to apoptosis to avoid becoming abnormal sperm. Sertoli cells phagocyte these apoptotic germ cells and degrade part of the cytoplasm of sperm during spermiogenesis. Arsa−/− mice had SGG accumulated in Sertoli cells, with lysosome swelling, impaired spermatogenesis and lower fecundity in vitro and in vivo, when males were older than 5 months (Xu et al., 2011). Additionally, increased levels of superoxide and hydrogen peroxide were found in Sertoli cells of Arsa−/− mice, which may explain the decrease in spermatogenesis and increased abnormal sperm population in this knockout model (Kongmanas et al., 2021). Tanphaichitr et al., 2018 highlighted the importance of SGG on male reproduction. Knockout mice for Cgt and Cst, two enzymes that act on SGG biosynthesis, also had their spermatogenesis disrupted.

Morales CR. et al. (2000), Morales C. R. et al. (2000) evaluated some male reproductive parameters in a mouse deficient of prosaposin, an enzyme that degrades sphingolipids. Prosaposin is targeted to lysosomes and processed into smaller molecules (saposins A, B, C, and D). The deficiency of saposin B and C results in metachromatic leukodystrophy and Gaucher diseases respectively. The knockout mouse presented small testes, epididymis, seminal vesicles and prostates; prostatic secretory cells were absent; and spermiogenesis was reduced. However, plasma testosterone was higher in knockout males compared to wild types. Prostate sections immunostained with antiandrogen receptor antibody were similar between groups, but the MAPK pathway was inactive in the mutant mice.

Körschen et al. (2013) worked with a GBA 2 knockout mouse. GBA 1 and GBA 2 are glucosidases that cleave glucosylceramide to glucose and ceramide. Mutation in GBA1 causes Gaucher disease. However, GBA 2 is localized in the endoplasmic reticulum and Golgi and has a strong association with cellular membranes. Studying GBA 2 may elucidate the pathophysiology of Gaucher disease. Its absence results in the storage of glucosylceramide in many tissues, including the testes, and impairs sperm development. Sperm with large round heads, abnormal acrosomes and defective motility were detected by Yildiz et al. (2006) using the same model.

Shen et al. (2015) detected increased androgen receptor (AR) signaling in a mouse model of Fabry disease with deficient α-galactosidase, which catabolizes glycosphingolipids. The blocking of AR signaling by castration or by treatment with an AR antagonist prevented cardiac and kidney hypertrophy, two common clinical manifestations of patients affected by Fabry disease. They concluded that the AR pathway interferes in the pathogenesis of the disease and suggested the blocking of this signaling as a novel therapeutic approach.

Some diseases are not directly related to a poor lysosomal enzymatic activity, but to a failure in the transport of some substrates or ions from cytoplasm to lysosomes and from lysosomes to cytoplasm. Some integral proteins transport lipid substrates to lysosomes and some ion channels regulate the lysosomal ionic environment. This molecular traffic is essential to regulate the cell signaling from cytoplasm to nucleus and also the intra-lysosomal metabolic pathways (Medina and Ballabio, 2015; Platt et al., 2018).

Erickson et al. (2002) evaluated a double mutant mouse (Npc−/− and Mdr−/−) model. This Npc−/− mouse mimics Niemmann-Pick Type C disease, a progressive neurological disease that interfere in cholesterol transport, not specifically in the activity of a lysosomal hydrolase. Despite normal folliculogenesis and normal progesterone levels, Npc−/− female mice were infertile and presented a lack of implantation because of abnormal cellular cholesterol homeostasis. However, Npc−/− and Mdr−/− double mutant females had their fertility recovered, as the Mdr gene codes a multiple drug resistance (MDR) P-glycoprotein, a plasma membrane protein implicated in the movement of drugs and lipids across membranes. While the neurological disease continued at its usual rate, preventing the females from taking care of their litters, double mutant females became fertile, which demonstrated the participation of a system of proteins in the control of cellular cholesterol transport.

Donohue et al. (2009) also evaluated a female model of Npc−/−, but in this specific model, fibrillary astrocytes expressed NPC1 protein, using glial fibrillary acidic protein (GFAP) promoter. This selective expression of NPC1 corrected sterility of Npc−/− females as a result of restoring hypothalamic control of the pituitary. These results were reinforced by Gévry et al. (2004). They used an Npc1−/− female model, and submitted them to a transplant of a kidney capsule from wild types. Females had their ovulation and formation of corpora lutea restored following this intervention. Gonadotropin treatment induced ovulation and restored the expression of steroidogenic proteins. Additionally, the chronic treatment of knockout females with 17-β-estradiol restored the volume of the pituitary gland, as well as prolactin expression and folliculogenesis. Thus, they also concluded that NPC1 interferes in the hypothalamic-pituitary-ovarian feedback loop and consequently affects estrogen production (Gévry et al., 2004). The same group detected the importance of this protein in respect of adrenal development and function (Gévry and Murphy 2002).

Busso et al. (2010) examined NPC2 knockout females. The NPC1 and NPC2 proteins function cooperatively to catalyze cholesterol efflux from lysosomes. It is known that NPC1 is expressed in ovarian cells and female NPC1 deficient mice are infertile. In this study, the authors evaluated the location of NPC2 in the female reproductive tract. Ovarian NPC2 was present in theca and luteal cells, which use cholesterol to produce estradiol and progesterone, respectively. Npc2−/− female mice had altered estrous cycles, were infertile, with normal folliculogenesis only until antral stage, but no formation of the luteal body. Serum estradiol was reduced and ovarian cholesterol was stored in knockout mice, suggesting a defect in cholesterol export from intracellular stores. The authors demonstrated that NPC2 played a role in the traffic of ovarian cholesterol which is required for steroid synthesis and to support follicle maturation, ovulation and luteinization.

Fan et al. (2006) evaluated the same Npc1−/− mice and detected morphological sperm defects, low sperm number in their epididymal cauda and that gametes did not interact efficiently with the pellucid zone of oocytes from wild-type females.

Xie et al. (2006) used Npc1−/− mice to evaluate three sources for the capture of cellular cholesterol: LDL derived cholesterol, de novo synthesis and scavenger receptor mediated uptake of HDL cholesteryl ester. The rates of net cholesterol acquisition by these three pathways were measured in the adrenal, ovary, and testes. Plasma concentrations of testosterone, progesterone and corticosterone were similar to controls or even elevated in Npc1−/− mice. Thus, according to the authors, the impairment of cholesterol acquisition through the NPC1-dependent, clathrin-coated pit pathway did not limit the availability of cholesterol substrate for steroid hormone synthesis in the steroidogenic cells. However, despite normal hormone conditions, significant evidence of reproductive damage was reported in many studies as a result of the unsuitable lipid storage in the cellular environment.

Roff et al. (1993) evaluated Npc1−/− mice and detected lower intratesticular testosterone production, small seminal vesicles, changes in seminiferous tubules and in Leydig cells. Hepatic sterol carrier proteins were studied by Roff et al. (1992) and they detected that the expression of these proteins varies according to sexual development. Their expression in male and female Npc1−/− mice declined during sexual maturing.

Wang et al. (2019) evaluated a model of mucolipidosis Type IV, caused by a deficiency of a lysosomal ion channel and not directly by a lysosomal hydrolase. The absence of the ionic channel interferes in lysosomal pH and 5-month-old females are completely unfertile. Progesterone deficiency was detected 4.5 days after the post coitum/gestation day. Histological analysis showed less defined corpus luteal, extensive luteal cell vacuolization and degeneration. This study demonstrated a novel function of this lysosomal ion channel in maintaining luteal cell integrity and function.

Taylor et al. (1989) evaluated dogs with fucosidosis, an LSD caused by genetic mutation of α-L-fucosidase. The enzymatic inactivity results in storage of glycoasparagines with terminal fucose residues in neurons and visceral tissues. The mutation in dogs, which is spontaneous, was associated with a range of significant reproductive damage, including to vacuoles in the testes and epididymis, reduced sperm number, abnormal sperm morphology and motility and altered surface glycoprotein composition during epididymal transit. Similar results were found by Veeramachaneni et al. (1998), who reported important spermatic damages and malformation of acrosomes.

Hu et al. (2012) studied a model of galactosialidosis, caused by the deficiency of serine carboxypeptidase protective protein/cathepsin A (PPCA). PPCA forms a complex with neuraminidase 1 (NEU1) and β-galactosidase (β-GAL). Patients with galactosialidosis develop a complete deficiency of NEU1 and a partial deficiency of β–GAL. Animals in male and female models are known to be infertile but after being injected with recombinant retroviral vectors expressing PPCA, their expression of PPCA and NEU1 recovered in reproductive tissues (testis, epididymis, ovary and uterus) and their fertility was restored.

Geist and Lüllmann-Rauch (1994) induced lipidosis with specific drugs and evaluated the effect on the estrous cycle and on the vaginal and uterine epithelia. After 2 weeks of continuous administration of chlorphentermine and imipramine, both drugs that interfere in lipid degradation, uterine and vaginal epithelia were vacuolated under ultrastructural examination and estrous cycle were stagnant as the lipidic storage interfered in steroidogenesis and all target organs and glands.

Ponce et al. (1999) observed the expression of acid glucosidase (GAA) in different tissues throughout mouse development. The expression of GAA was higher in Sertoli cells in comparison to other cell types. GAA is a lysosomal enzyme that cleaves glycogen and its absence results in Pompe disease.

Some studies did not use a specific LSD model, but explored the influence of lysosomal enzymes on germ cells and reproductive tissues. Hermo and Andonian (2003) evaluated two lysosomal enzymes: cathepsin D and sulphated glycoprotein 1 (SGP) in the epididymis. Their findings reinforced the importance of both hydrolases on endocytosis throughout the epididymal ducts in respect of sperm maturation. Another study reported that the activity of β-hexosaminidase is many times higher in the epididymis than in other tissues. The enzyme was detected in Sertoli cells, in the testicular interstitium and in epithelial cells of the epididymis (Hermo et al., 1997), evidencing the importance of this lysosomal hydrolase to a coordinated male germ cell production and maturing.