Engineering 3D micro-compartments for highly efficient and scale-independent expansion of human pluripotent stem cells in bioreactors.

Human pluripotent stem cells (hPSCs) have emerged as the most promising cellular source for cell therapies. To overcome the scale-up limitations of classical 2D culture systems, suspension cultures have been developed to meet the need for large-scale culture in regenerative medicine. Despite constant improvements, current protocols that use microcarriers or generate cell aggregates only achieve moderate amplification performance. Here, guided by reports showing that hPSCs can self-organize in vitro into cysts reminiscent of the epiblast stage in embryo development, we developed a physio-mimetic approach for hPSC culture. We engineered stem cell niche microenvironments inside microfluidics-assisted core-shell microcapsules. We demonstrate that lumenized three-dimensional colonies significantly improve viability and expansion rates while maintaining pluripotency compared to standard hPSC culture platforms such as 2D cultures, microcarriers, and aggregates. By further tuning capsule size and culture conditions, we scale up this method to industrial-scale stirred tank bioreactors and achieve an unprecedented hPSC amplification rate of 277-fold in 6.5 days. In brief, our findings indicate that our 3D culture system offers a suitable strategy both for basic stem cell biology experiments and for clinical applications.

Purification of Synaptosome Populations Using Fluorescence-Activated Synaptosome Sorting.

For several decades, neurobiologists have used subcellular fractionation methods to analyze the molecular structure and some functional features of the cells in the central nervous system. Indeed, brain tissue contains a complex intermingled network of neuronal, glial, and vascular cells. To reduce this complexity biochemists have optimized fractionation protocols that enrich in specific compartments such as synapses (called "synaptosomes") and synaptic vesicles, for example. However, recently, these approaches suffered from a lack of specificity and purity. In a recent effort, we extended the conventional synaptosome preparation to purify fluorescent synaptosomes on a cell sorter. We could prove that our method allows for the steep enrichment in fluorescent excitatory VGLUT1venus synaptosomes containing the presynaptic element and the tip of the post-synaptic element and a strong depletion in neuronal and glial contaminants. Here, we propose a detailed procedure for the implementation of Fluorescence Activated Synaptosome Sorting.

Proteomic screening of glutamatergic mouse brain synaptosomes isolated by fluorescence activated sorting.

For decades, neuroscientists have used enriched preparations of synaptic particles called synaptosomes to study synapse function. However, the interpretation of corresponding data is problematic as synaptosome preparations contain multiple types of synapses and non-synaptic neuronal and glial contaminants. We established a novel Fluorescence Activated Synaptosome Sorting (FASS) method that substantially improves conventional synaptosome enrichment protocols and enables high-resolution biochemical analyses of specific synapse subpopulations. Employing knock-in mice with fluorescent glutamatergic synapses, we show that FASS isolates intact ultrapure synaptosomes composed of a resealed presynaptic terminal and a postsynaptic density as assessed by light and electron microscopy. FASS synaptosomes contain bona fide glutamatergic synapse proteins but are almost devoid of other synapse types and extrasynaptic or glial contaminants. We identified 163 enriched proteins in FASS samples, of which FXYD6 and Tpd52 were validated as new synaptic proteins. FASS purification thus enables high-resolution biochemical analyses of specific synapse subpopulations in health and disease.