Decapacitation Factor
Definition and Function
Decapacitation factors are components of seminal plasma that prevent premature capacitation of spermatozoa by stabilizing the sperm membrane and maintaining the physiological cholesterol/phospholipid ratio. 1
Molecular Composition and Mechanism
Decapacitation factors arise from the interaction between three key components 1:
- Cholesterol - maintains membrane stability
- Phospholipids - regulates membrane fluidity
- Fibronectin-like substance - provides structural support
These components are delivered via small vesicles in seminal plasma and work by preventing the premature onset of capacitation through sperm membrane stabilization. 1
Specific Identified Decapacitation Factors
Multiple proteins have been identified as decapacitation factors through mass spectrometry analysis 2:
- Phosphatidylethanolamine binding protein 1 (PBP) - identified as a primary candidate decapacitation factor 2
- Cysteine-rich secretory protein 1 (CRISP1) 2
- Plasma membrane fatty acid binding protein 2
- Serine protease inhibitor Kazal type 3 (SPINK3) - binds to lipid rafts on sperm membrane 3
- Seminal vesicle autoantigen (SVA) - targets membrane sphingomyelin and regulates plasma membrane Ca²⁺-ATPase (PMCA) activity 4
Mechanism of Action
Decapacitation factors work through several interconnected pathways 4, 2:
- Membrane stabilization - binding to lipid rafts prevents premature membrane changes 3
- Calcium regulation - SVA decreases intracellular calcium by regulating PMCA activity 4
- cAMP suppression - reduced calcium leads to decreased cAMP levels, preventing premature capacitation 4
- Tyrosine phosphorylation inhibition - suppresses phosphorylation in the sperm plasma membrane 2
- Acrosome reaction inhibition - prevents premature acrosome reaction 5, 2
Removal During Capacitation
Decapacitation factors must be removed from the sperm surface for successful capacitation and fertilization to occur. 5, 3
The removal process occurs through 3:
- In vitro capacitation - factors are released during 18-hour incubation in capacitating medium 5
- In vivo removal - uterine fluid from estrus females removes these factors 3
- Sequential removal - SPINK3 is removed first from the apical region in the uterus, then from the flagellar region in the oviduct 3
Origin of Decapacitation Factors
These proteins are produced by 5, 2:
The glycoprotein released during capacitation reacts with antibodies against seminal plasma from vasectomized donors but not with antibodies against epididymal proteins, confirming accessory gland origin. 5
Clinical Relevance
Understanding decapacitation factors has potential implications for 1:
- Male infertility diagnosis - abnormal decapacitation factor function may explain some cases of unexplained male infertility 1
- Male contraception development - could provide basis for specific and reversible contraceptive methods 1
Timing Considerations in Assisted Reproduction
The removal of decapacitation factors is critical for proper timing of insemination, as premature capacitation leads to sperm apoptosis while delayed capacitation results in spermatozoa unable to recognize oocytes. 6
After natural intercourse, spermatozoa attach to the isthmus epithelium where binding keeps them viable and prevents premature capacitation until ovulation signals trigger hyperactivated movement toward the oocyte. 6