Globozoospermia is a rare and difficult to overcome male infertility condition. A team of researchers headed up by Jun Xia of The Hong Kong University of Science and Technology, in the People's Republic of China, found that mice who lack the protein known as PICK1 are infertile due to a condition that looks very much like human male globozoospermia. The research team hopes this finding might help the medical community to better understand this type of infertility, so that new treatments might be developed, leading to higher rates of conception in those couples trying to conceive (TTC).
In globozoospermia, the heads of individual sperm are too round-headed. How much of a stumbling block this presents to conception depends upon the ratio of these abnormal sperm to other healthier, more normal sperm, which may also be present in the man's semen. The round-headed spermatozoa result from defects in the spermatogenesis process which leads to a malformation of the acrosome.
The acrosome is a section of the sperm that contains the necessary proteins to dissolve the egg's external membrane. This enables the sperm to enter and fertilize the egg. The acrosome therefore serves an integral function during the fertilization process at the point where sperm must bind to the zona pellucida, the external membrane of the egg.
In the most severe cases of globozoospermia, the acrosome is altogether absent. The round-headed sperm not only display an abnormal nuclear shape, but they also present with an abnormal arrangement of the mitochondria of the spermatozoon.
In the Hong Kong University study, the male mice missing the PICK1 protein were found to have a low sperm count. Those sperm that were produced appeared abnormal with the characteristic round heads seen in human globozoospermia. Furthermore, the sperm had a severe impairment of motility (movement). On closer examination, it was revealed that the acrosomes were malformed.
The researchers found that PICK1 interacts with two proteins, GOPC and CK2-alpha quite close to the area of those cellular structures which form the acrosomes. The authors of the study posit that PICK1 plays a crucial role in the formation of the acrosomes. It may be too early to postulate a theory, but if men with globozoospermia were also found to have low levels of PICK1 and if it were possible to replace or restore this protein, sperm health and fertility might also be restored.