Metabolism of SpermatozoaMetabolism of Spermatozoa

Rahul KatiyarPhD ScholarRoll No.- P-1856

WHY METABOLISM NEEDED?WHY METABOLISM NEEDED?

Spermatozoa dynamic structure

The sperm require a continuous supply of ATP to maintain motility in the male and female reproductive tract

During epididymal maturation and later in the female reproductive tract when they undergo capacitation and hyperactivation

PATHWAYS OF ENERGY PRODUCTION IN PATHWAYS OF ENERGY PRODUCTION IN SPERMATOZOASPERMATOZOA

Metabolism: Anaerobic & Aerobic Respiration

ATP production by oxidative phosphorylation & glycolysis

ATP PRODUCTION SITES IN SPERMATOZOAATP PRODUCTION SITES IN SPERMATOZOA

Machinery for oxidative phosphorylation Mid-Piece

Glycolytic enzymes tethered to the fibrous sheath of the principal piece

(Storey and Kayne 1975; Krisfalusi et al. 2006, Plessis et al., 2015)

SITE OF ATP PRODUCTION VIA SITE OF ATP PRODUCTION VIA OXIDATIVE PHOSPHORYLATIONOXIDATIVE PHOSPHORYLATION

Mitochondria referred as power house of cell.

Occupies substantial portion of total cellular volume ( 15-22%).

Mature spermatozoa contains approx. 72-80 mitochondria.

CRISTAE are principle sites of OXPHOS and ATP generation

Sperm mitochondria possess Cytochrome c ( Nariswa et al., 2002) , Hexokinase subunit VIb of cytochrome C Oxidase( Huttemann et al., 2003) and lactate dehydrogenase (Blanco et al., 1963).

SITE OF ATP PRODUCTION VIA SITE OF ATP PRODUCTION VIA GLYCOLYSISGLYCOLYSIS

Head and principle piece are devoid of respiratory enzymes.

Several glycolytic enzymes have been found in fibrous sheath of spermatozoa which include-

HexokinasePhosphoglucokinase isomerasePhosphofructokinaseGlyceraldehyde-3- phosphate dehydrogenase

( Kim et al., 2007)

Energy substrates Energy substrates • Glycolytic substrates: Glucose, mannose, fructose,

and sorbitol

• Non-glycolysable substrates: pyruvate, lactate, and hydroxybutyrate

• Glucose, mannose, fructose, and sorbitol high percentage of motile sperm and support the increase in phosphorylation

• Fructose and sorbitol does not support hyperactivation (Goodson et al., 2012 )

• Bull sperms prefer glucose over fructose

• Non-glycolysable substrates maintain motility with only low levels of tyrosine phosphorylation and hyperactivation

• Pyruvate, lactate able to sustain high ATP levels

• Citrate not able

• Citrate is not permeable to mitochondria

• Needs to be converted to malate with the use of ATP to be able to enter the citric acid cycle

GlycolysisGlycolysis Provides less efficient, but very high - throughout production

of ATP locally down the length of the principal piece Net yield of 2 molecules of ATP per molecule of glucose

oxidized Glycolysable substrates must be able to pass through the

plasma membrane of the flagellum

In the flagella of murine sperm GLUT3 is the primary facilitative glucose transporter (Simpson et al. 2008)

In bovine sperm uptake of is mediated by GLUT5 (Angulo et al. 1998)

Most of the steps in this process are catalyzed by sperm-specific isoforms of the respective proteins

Pyruvate is used to regenerate NAD+ from NADH converted into lactate by LDH

The NAD regeneration is essential for continuing glycolysis

TCA Cycle

Oxidative Phosphorylation

Glycolysis or Oxidative Glycolysis or Oxidative Phosphorylation???Phosphorylation???

Controversy over the relative importance of glycolysis and oxidative phosphorylation

It is suggested that sperm glycolysis is the main pathway to support motility.

(Miki et al. 2004)

Evidence for functional importance of glycolysis –

Glucose, but not lactate or pyruvate, is required for the protein tyrosine phosphorylation -- events observed during the process of sperm capacitation

(Travis et al. 2001)

Inhibiting electron transfer or uncoupling oxidative respiration did not impact the sperm’s ability to regulate patterns of motility

(Travis et al. 2001)

Inhibition of mitochondrial function was found not to impair motility and to have little effect on intracellular ATP levels (Mukai and Okuno 2004)

Addition of DOG (2-deoxyglucose) inhibited motility and led to depletion of ATP

(Mukai and Okuno 2004)

Gene knock out of the germ cell specific isoform of GAPDH defects in sperm motility and fertility

( Miki et al., 2004)

Large amounts of ATP are required along the full length of the motile flagellum

ATP produced by the mid piece mitochondria unable to diffuse sufficiently along the length of the FS to supply the entire flagellum to support the axonemal dynein ATPase

Humans appear to be one mammalian species whose sperm do rely substantially, if not entirely, on glycolysis for motility

(Ford and Rees, 1990; Williams and Ford, 2001)

Measurement of metabolismMeasurement of metabolismRate of anaerobic glycolysis:• ZN

2LA Expressed as number of units of lactic acid

produced by a standard number of sperm cells (100 × 106 sperm) in a given time (1 hour)

• For good quality spermatozoa-- 200µg

• Fructolytic index the mg of fructose used by 1 billion spermatozoa in 1 hr at 37° C under anaerobic conditions.

• Normal value 1.5 – 2 mg/billion cells

Measurement of aerobic respiration• By Metylene blue reduction test or resazurine

reduction test

• Direct determination of O2 consumption in microrespirometers (Warburg respirometer)

• ZO2 = µl of O2 consumed by 100X106 cells in 1 hr at 37o C.

• Normal value- 21

Factors influencing metabolic rates Factors influencing metabolic rates of bull spermatozoaof bull spermatozoa

TemperatureCell concentration Inorganic PpHCationsAnionsOsmotic pressureHormonesAnti-bacterial agents

ConclusionConclusionGlycolysis provides less efficient, but very high-

throughout production of ATP locally down the length of the principal piece

Mitochondrial respiration and glycolysis can compensate for each other but they do not have obligatory roles in maintaining sperm ATP production and sperm motility

Thank You