The role of calcium stores in calcium signalling in human sperm

Morris, Jennifer Toni (2014). The role of calcium stores in calcium signalling in human sperm. University of Birmingham. Ph.D.

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Abstract

Calcium (Ca\(^{2+}\)) signalling is implicated in the regulation of numerous sperm processes elemental for fertilisation including the acrosome reaction, hyperactivated motility (HA) and capacitation. A number of studies have identified components of Ca\(^{2+}\) storage organelles in human sperm, including inositol-1,4,5 triphosphate receptors IP3Rs, secretory pathway calcium ATPases (SPCA), ryanodine receptors (RyR) and the store operated calcium entry (SOCE) channels STIM and Orai, all of which are associated with the acrosome and posterior head/neck region of the sperm (PHN). In 2005, Herrick et al., characterised the Ca\(^{2+}\) storage capacity of mammalian acrosomes; however the identity of the PHN Ca\(^{2+}\) store is less clear. The aim of this study was to characterise the PHN Ca\(^{2+}\) store to determine the relationship between store mobilisation and HA in human sperm. We observed localisation of high Ca\(^{2+}\) at the PHN and midpiece of human sperm. Treatment with mitochondrial uncouplers CCCP and DNP elevated [Ca\(^{2+}\)]\(_i\) and depolarised the mitochondrial membrane potential (MMP) consistent with mobilisation of mitochondrial Ca\(^{2+}\) stores. However pre-treatment with mitochondrial uncouplers had no significant effect on the characteristic biphasic [Ca\(^{2+}\)]\(_i\) increase associated with progesterone. Conversely prior mobilisation of stored Ca\(^{2+}\) with thimerosal (IP3R activator) or pre-treatment with SKF-96365 (SOCE inhibitor) significantly reduced the sustained component of the biphasic [Ca\(^{2+}\)]\(_i\) response, whilst treatment with 2-APB or SKF (SOCE modulators) enhanced the progesterone induced [Ca\(^{2+}\)]\(_i\) transient. In addition treatment with novel Orai targeted bioportides results in a significant prolongation of the progesterone-induced [Ca\(^{2+}\)]\(_i\), apparently due to non-reversible SOCE activation, initiated during the transient. These results indicate the presence of at least two discrete Ca\(^{2+}\) stores at the PHN which contribute separately to the biphasic progesterone [Ca\(^{2+}\)]\(_i\) increase and a role for STIM/Orai mediated SOCE in both transient and sustained components of the progesterone-induced [Ca\(^{2+}\)]\(_i\) signal in human sperm.

Type of Work:

Thesis (Doctorates > Ph.D.)

Award Type:

Doctorates > Ph.D.

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