PSEN1ΔE9, APPswe, and APOE4 Confer Disparate Phenotypes in Human iPSC-Derived Microglia.

Here we elucidate the effect of Alzheimer disease (AD)-predisposing genetic backgrounds, APOE4, PSEN1ΔE9, and APPswe, on functionality of human microglia-like cells (iMGLs). We present a physiologically relevant high-yield protocol for producing iMGLs from induced pluripotent stem cells. Differentiation is directed with small molecules through primitive erythromyeloid progenitors to re-create microglial ontogeny from yolk sac. The iMGLs express microglial signature genes and respond to ADP with intracellular Ca2+ release distinguishing them from macrophages. Using 16 iPSC lines from healthy donors, AD patients and isogenic controls, we reveal that the APOE4 genotype has a profound impact on several aspects of microglial functionality, whereas PSEN1ΔE9 and APPswe mutations trigger minor alterations. The APOE4 genotype impairs phagocytosis, migration, and metabolic activity of iMGLs but exacerbates their cytokine secretion. This indicates that APOE4 iMGLs are fundamentally unable to mount normal microglial functionality in AD.

The Ubiquitin Proteasome System Is a Key Regulator of Pluripotent Stem Cell Survival and Motor Neuron Differentiation.

The ubiquitin proteasome system (UPS) plays an important role in regulating numerous cellular processes, and a dysfunctional UPS is thought to contribute to motor neuron disease. Consequently, we sought to map the changing ubiquitome in human iPSCs during their pluripotent stage and following differentiation to motor neurons. Ubiquitinomics analysis identified that spliceosomal and ribosomal proteins were more ubiquitylated in pluripotent stem cells, whilst proteins involved in fatty acid metabolism and the cytoskeleton were specifically ubiquitylated in the motor neurons. The UPS regulator, ubiquitin-like modifier activating enzyme 1 (UBA1), was increased 36-fold in the ubiquitome of motor neurons compared to pluripotent stem cells. Thus, we further investigated the functional consequences of inhibiting the UPS and UBA1 on motor neurons. The proteasome inhibitor MG132, or the UBA1-specific inhibitor PYR41, significantly decreased the viability of motor neurons. Consistent with a role of the UPS in maintaining the cytoskeleton and regulating motor neuron differentiation, UBA1 inhibition also reduced neurite length. Pluripotent stem cells were extremely sensitive to MG132, showing toxicity at nanomolar concentrations. The motor neurons were more resilient to MG132 than pluripotent stem cells but demonstrated higher sensitivity than fibroblasts. Together, this data highlights the important regulatory role of the UPS in pluripotent stem cell survival and motor neuron differentiation.

Müller glia factors induce survival and neuritogenesis of peripheral and central neurons.

We have examined the trophic effects of conditioned media obtained from purified murine Müller glia cells on chick purified sympathetic or dorsal root ganglia (DRG) neurons and on Retinal Ganglion Cells (RGC) from postnatal mice. Purified murine Müller glia cultures stained positively for vimentin, GFAP or S-100, but were negative for neuronal markers. Murine Müller glial conditioned medium (MMG) was concentrated and at 1:1 dilution supported 100% survival of chick or rat sympathetic neurons after 48 h compared to <5% in controls. Partial purification of the MMG using centriprep concentrators showed that trophic activity is from molecules above 10 kDa. MMG stimulated AKT, ERK and pStat3 in sympathetic neurons. Sympathetic or DRG neuronal survival induced by MMG was blocked by anti-human NGF, but not by anti-human CNTF (sympathetic) or by anti-BDNF (DRGs) neutralizing antibodies. MMG also induced neurite outgrowth in P4 mice retinal explants and on isolated RGC. RGCs plated on top of Müller glia cells had a much better survival rate (>80%, 96 h) compared to laminin+poly-L-lysine substrates. In conclusion, we show that purified mice Müller glia cultures secrete NGF that support peripheral neuronal survival and other unidentified trophic molecules that induce RGC survival and neuritogenesis.