The relevance of sperm morphology in male infertility

Abstract

This brief report concerns the role of human sperm morphology assessment in different fields of male infertility: basic research, genetics, assisted reproduction technologies, oxidative stress. One of the best methods in studying sperm morphology is transmission electron microscopy (TEM) that enables defining the concept of sperm pathology and classifying alterations in non-systematic and systematic. Non-systematic sperm defects affect head and tail in variable ratio, whereas the rare systematic defects are characterized by a particular anomaly that marks most sperm of an ejaculate. TEM analysis and fluorescence in situ hybridization represent outstanding methods in the study of sperm morphology and cytogenetic in patients with altered karyotype characterizing their semen quality before intracytoplasmic sperm injection. In recent years, the genetic investigations on systematic sperm defects, made extraordinary progress identifying candidate genes whose mutations induce morphological sperm anomalies. The question if sperm morphology has an impact on assisted fertilization outcome is debated. Nowadays, oxidative stress represents one of the most important causes of altered sperm morphology and function and can be analyzed from two points of view: 1) spermatozoa with cytoplasmic residue produce reactive oxygen species, 2) the pathologies with inflammatory/oxidative stress background cause morphological alterations. Finally, sperm morphology is also considered an important endpoint in in vitro experiments where toxic substances, drugs, antioxidants are tested. We think that the field of sperm morphology is far from being exhausted and needs other research. This parameter can be still considered a valuable indicator of sperm dysfunction both in basic and clinical research.

Keywords: assisted reproduction technologies (ART); genetics; human sperm; oxidative stress; sperm morphology; systematic sperm defects; transmission electron microscopy.

Figure 1

Transmission electron microscopy (TEM) micrographs of longitudinal sections of immature (A), necrotic (B) and apoptotic sperm (C). Immature sperm (A) is characterized by irregular nucleus with uncondensed chromatin (uCh). Cytoplasmic residue (CR) embeds swollen mitochondria (M) and coiled disassembled axoneme (Ax). Necrotic sperm (B) shows an altered nucleus with disrupted chromatin (dCh), swollen mitochondria (M) and broken plasma membrane (arrow). In figure (C) two apoptotic sperm with marginated chromatin (mCh), acrosome (Ac) far from the nucleus, integer plasma membranes (arrow) are shown. Bars A, B, C: 2μm.

Figure 2

Transmission electron microscopy (TEM) micrograph of sperm with globozoospermia. The round-shaped heads were devoid of acrosome, the nuclei show uncondensed chromatin (uCh) characterized by granular texture. Bar: 3.5 μm.

Figure 3

Transmission electron microscopy (TEM) micrograph of a sperm with a combination of flagellar alterations: hyperplastic fibrous sheath (Dysplasia of fibrous sheath, DFS) and almost detached tail (arrow); in addition, altered nucleus and acrosome are visible. Bar: 3.5 μm.

Figure 4

Transmission electron microscopy (A) and UV (B) micrographs of binucleated, diploid sperm. Figure (A) shows two nuclei embedded in a large cytoplasmic residue (CR) where the tail (Ax) is coiled. The acrosome (Ac) is mislocated. Figure (B) shows fluorescence in situ hybridization with probes for chromosome 18 (green) and 9 (red). The nucleus is diploid since shows two spots of each chromosome. Sperm nucleus is stained with DAPI (blue). Bar A: 3.5 μm.