Journal Article

Intracellular translocation and differential accumulation of cell-penetrating peptides in bovine spermatozoa: evaluation of efficient delivery vectors that do not compromise human sperm motility

Sarah Jones, Monika Lukanowska, Julia Suhorutsenko, Senga Oxenham, Christopher Barratt, Steven Publicover, Dana Maria Copolovici, Ülo Langel and John Howl

in Human Reproduction

Published on behalf of European Society of Human Reproduction and Embryology

Volume 28, issue 7, pages 1874-1889
Published in print July 2013 | ISSN: 0268-1161
Published online April 2013 | e-ISSN: 1460-2350 | DOI: http://dx.doi.org/10.1093/humrep/det064
Intracellular translocation and differential accumulation of cell-penetrating peptides in bovine spermatozoa: evaluation of efficient delivery vectors that do not compromise human sperm motility

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STUDY QUESTION

Do cell penetrating peptides (CPPs) translocate into spermatozoa and, if so, could they be utilized to deliver a much larger protein cargo?

SUMMARY ANSWER

Chemically diverse polycationic CPPs rapidly and efficiently translocate into spermatozoa. They exhibit differential accumulation within intracellular compartments without detrimental influences upon cellular viability or motility but they are relatively ineffective in transporting larger proteins.

WHAT IS ALREADY KNOWN

Endocytosis, the prevalent route of protein internalization into eukaryotic cells, is severely compromised in mature spermatozoa. Thus, the translocation of many bioactive agents into sperm is relatively inefficient. However, the delivery of bioactive moieties into mature spermatozoa could be significantly improved by the identification and utility of an efficient and inert vectorial delivery technology.

STUDY DESIGN

CPP translocation efficacies, their subsequent differential intracellular distribution and the influence of peptides upon viability were determined in bovine spermatozoa. Temporal analyses of sperm motility in the presence of exogenously CPPs utilized normozoospermic human donor samples.

MATERIALS AND METHODS

CPPs were prepared by manual, automated and microwave-enhanced solid phase synthesis. Confocal fluorescence microscopy determined the intracellular distribution of rhodamine-conjugated CPPs in spermatozoa. Quantitative uptake and kinetic analyses compared the translocation efficacies of chemically diverse CPPs and conjugates of biotinylated CPPs and avidin. 3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium, inner salt (MTS) conversion assays were employed to analyse the influence of CPPs upon sperm cell viability and sperm class assays determined the impact of CPPs on motility in capacitated and non-capacitated human samples.

MAIN RESULTS

Chemically heterogeneous CPPs readily translocated into sperm to accumulate within discrete intracellular compartments. Mitoparan (INLKKLAKL(Aib)KKIL), for example, specifically accumulated within the mitochondria located in the sperm midpiece. The unique plasma membrane composition of sperm is a critical factor that directly influences the uptake efficacy of structurally diverse CPPs. No correlations in efficacies were observed when comparing CPP uptake into sperm with either uptake into fibroblasts or direct translocation across a phosphatidylcholine membrane. These comparative investigations identified C105Y (CSIPPEVKFNKPFVYLI) as a most efficient pharmacokinetic modifier for general applications in sperm biology. Significantly, CPP uptake induced no detrimental influence upon either bovine sperm viability or the motility of human sperm. As a consequence of the lack of endocytotic machinery, the CPP-mediated delivery of much larger protein complexes into sperm is relatively inefficient when compared with the similar process in fibroblasts.

LIMITATIONS, REASONS FOR CAUTION

It is possible that some CPPs could directly influence aspects of sperm biology and physiology that were not analysed in this study.

WIDER IMPLICATIONS OF THE FINDINGS

CPP technologies have significant potential to deliver selected bioactive moieties and so could modulate the biology and physiology of human sperm biology both prior- and post-fertilization.

STUDY FUNDING/COMPETING INTERSTS

We are pleased to acknowledge financial support from the following sources: the Wellcome Trust, TENOVUS (Scotland), University of Dundee, Medical Research Council, NHS Tayside and Scottish Enterprise and the Research Institute in Healthcare Science, University of Wolverhampton. No conflicts of interest are reported by the authors.

Keywords: spermatozoa; cell-penetrating peptide; membrane translocation; cytotoxicity; motility; mitochondrion

Journal Article.  8536 words.  Illustrated.

Subjects: Reproductive Medicine

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