Effect of serum replacement on murine spermatogonial stem cell cryopreservation

Comparison of different freezing rates on post-thaw viability, proliferation, and stemness of sheep spermatogonial stem cells

The application of spermatogonial stem cells (SSC) will be more effective and feasible following the successful cryopreservation and transfer of SSCs in livestock. Like other cells, SSCs are also sensitive to cryoinjury; hence composition of the cryomedia and freezing protocols need to be optimized. The present study aims to optimize the best freezing rates by minimising the ice crystallization and dehydration effect in order to maximize the post-thaw SSCs survivability and stemness characteristics. Three different freezing protocols with varied cooling profiles, cooling profile 1 (isopropanol based freezing): 1 °C/min from 0 °C to -10 °C, 0.5 °C/min up to -40 °C, further reduced to 0.25 °C/min up to -50 °C and 0.1 °C/min to -60 °C; cooling profile 2 (using programmable freezer): 1 °C/min up to 4 °C, 0.3 °C/min up to -8 °C, and cooled at 0.5 °C/min to -50 °C, further decrease to -90 °C (8 °C/min) and cooling profile 3 (uncontrolled rapid freezing): 3.3 °C/min from 0 °C to -10 °C, 5 °C/min up to -40 °C, 2 °C/min to -50 °C and 1.2 °C/min up to -60 °C, were compared for cryopreservation efficiency. The overall viability (91.41 ± 2.00 % Vs 74.59 ± 2.34 %), stemness activity (1.34 ± 0.095 OD units Vs 0.356 ± 0.026 OD units), and proliferation rate (0.849 ± 0.019 OD units Vs 0.749 ± 0.015 OD units) of post-thaw SSC culture irrespective of the freezing regimes were significantly decreased when compared to pre-freeze SSC culture characteristics. The post-thaw viability was significantly greater in cooling profile 1 (79.64 ± 4.1 %) when compared to cooling profile 2 (69.72 ± 2.4 %) and cooling profile 3 (75.43 ± 4.8 %). Also, cooling profile 1 yielded greater (p < 0.05) post-thaw stemness activity (0.456 ± 0.044 OD units) when compared to other methods. The study suggests that the cooling profile 1 using isopropanol based freezing can be recommended for preservation of viability and stemness characteristics of SSCs.

The Role of Promyelocytic Leukemia Zinc Finger (PLZF) and Glial-Derived Neurotrophic Factor Family Receptor Alpha 1 (GFRα1) in the Cryopreservation of Spermatogonia Stem Cells

The cryopreservation of spermatogonia stem cells (SSCs) has been widely used as an alternative treatment for infertility. However, cryopreservation itself induces cryoinjury due to oxidative and osmotic stress, leading to reduction in the survival rate and functionality of SSCs. Glial-derived neurotrophic factor family receptor alpha 1 (GFRα1) and promyelocytic leukemia zinc finger (PLZF) are expressed during the self-renewal and differentiation of SSCs, making them key tools for identifying the functionality of SSCs. To the best of our knowledge, the involvement of GFRα1 and PLZF in determining the functionality of SSCs after cryopreservation with therapeutic intervention is limited. Therefore, the purpose of this review is to determine the role of GFRα1 and PLZF as biomarkers for evaluating the functionality of SSCs in cryopreservation with therapeutic intervention. Therapeutic intervention, such as the use of antioxidants, and enhancement in cryopreservation protocols, such as cell encapsulation, cryoprotectant agents (CPA), and equilibrium of time and temperature increase the expression of GFRα1 and PLZF, resulting in maintaining the functionality of SSCs. In conclusion, GFRα1 and PLZF have the potential as biomarkers in cryopreservation with therapeutic intervention of SSCs to ensure the functionality of the stem cells.

Macromolecular cryoprotectants for the preservation of mammalian cell culture: lessons from crowding, overview and perspectives

Cryopreservation is a process used for the storage of mammalian cells at a very low temperature, in a state of 'suspended animation.' Highly effective and safe macromolecular cryoprotectants (CPAs) have gained significant attention as they obviate the toxicity of conventional CPAs like dimethyl sulfoxide (DMSO) and reduce the risks involved in the storage of cultures at liquid nitrogen temperatures. These agents provide cryoprotection through multiple mechanisms, involving extracellular and intracellular macromolecular crowding, thereby impacting the biophysical and biochemical dynamics of the freezing medium and the cryopreserved cells. These CPAs vary in their structures and physicochemical properties, which influence their cryoprotective activities. Moreover, the introduction of polymeric crowders in the cryopreservation media enables serum-free storage at low-DMSO concentrations and high-temperature vitrification of frozen cultures (-80 °C). This review highlights the need for macromolecular CPAs and describes their mechanisms of cryopreservation, by elucidating the role of crowding effects. It also classifies the macromolecules based on their chemistry and their structure-activity relationships. Furthermore, this article provides perspectives on the factors that may influence the outcomes of the cell freezing process or may help in designing and evaluating prospective macromolecules. This manuscript also includes case studies about cellular investigations that have been conducted to demonstrate the cryoprotective potential of macromolecular CPAs. Ultimately, this review provides essential directives that will further improve the cell cryopreservation process and may encourage the use of macromolecular CPAs to fortify basic, applied, and translational research.

Current scenario and challenges ahead in application of spermatogonial stem cell technology in livestock

PURPOSE

Spermatogonial stem cells (SSCs) are the source for the mature male gamete. SSC technology in humans is mainly focusing on preserving fertility in cancer patients. Whereas in livestock, it is used for mining the factors associated with male fertility. The review discusses the present status of SSC biology, methodologies developed for in vitro culture, and challenges ahead in establishing SSC technology for the propagation of superior germplasm with special reference to livestock.

METHOD

Published literatures from PubMed and Google Scholar on topics of SSCs isolation, purification, characterization, short and long-term culture of SSCs, stemness maintenance, epigenetic modifications of SSCs, growth factors, and SSC cryopreservation and transplantation were used for the study.

RESULT

The fine-tuning of SSC isolation and culture conditions with special reference to feeder cells, growth factors, and additives need to be refined for livestock. An insight into the molecular mechanisms involved in maintaining stemness and proliferation of SSCs could facilitate the dissemination of superior germplasm through transplantation and transgenesis. The epigenetic influence on the composition and expression of the biomolecules during in vitro differentiation of cultured cells is essential for sustaining fertility. The development of surrogate males through gene-editing will be historic achievement for the foothold of the SSCs technology.

CONCLUSION

Detailed studies on the species-specific factors regulating the stemness and differentiation of the SSCs are required for the development of a long-term culture system and in vitro spermatogenesis in livestock. Epigenetic changes in the SSCs during in vitro culture have to be elucidated for the successful application of SSCs for improving the productivity of the animals.