Ca2+ administration prevents α-synuclein proteotoxicity by stimulating calcineurin-dependent lysosomal proteolysis.

The capacity of a cell to maintain proteostasis progressively declines during aging. Virtually all age-associated neurodegenerative disorders associated with aggregation of neurotoxic proteins are linked to defects in the cellular proteostasis network, including insufficient lysosomal hydrolysis. Here, we report that proteotoxicity in yeast and Drosophila models for Parkinson's disease can be prevented by increasing the bioavailability of Ca2+, which adjusts intracellular Ca2+ handling and boosts lysosomal proteolysis. Heterologous expression of human α-synuclein (αSyn), a protein critically linked to Parkinson's disease, selectively increases total cellular Ca2+ content, while the levels of manganese and iron remain unchanged. Disrupted Ca2+ homeostasis results in inhibition of the lysosomal protease cathepsin D and triggers premature cellular and organismal death. External administration of Ca2+ reduces αSyn oligomerization, stimulates cathepsin D activity and in consequence restores survival, which critically depends on the Ca2+/calmodulin-dependent phosphatase calcineurin. In flies, increasing the availability of Ca2+ discloses a neuroprotective role of αSyn upon manganese overload. In sum, we establish a molecular interplay between cathepsin D and calcineurin that can be activated by Ca2+ administration to counteract αSyn proteotoxicity.

Organoids to Study Intestinal Nutrient Transport, Drug Uptake and Metabolism - Update to the Human Model and Expansion of Applications.

Intestinal transport and sensing processes and their interconnection to metabolism are relevant to pathologies such as malabsorption syndromes, inflammatory diseases, obesity and type 2 diabetes. Constituting a highly selective barrier, intestinal epithelial cells absorb, metabolize, and release nutrients into the circulation, hence serving as gatekeeper of nutrient availability and metabolic health for the whole organism. Next to nutrient transport and sensing functions, intestinal transporters including peptide transporter 1 (PEPT1) are involved in the absorption of drugs and prodrugs, including certain inhibitors of angiotensin-converting enzyme, protease inhibitors, antivirals, and peptidomimetics like ß-lactam antibiotics. Here, we verify the applicability of 3D organoids for in vitro investigation of intestinal biochemical processes related to transport and metabolism of nutrients and drugs. Establishing a variety of methodologies including illustration of transporter-mediated nutrient and drug uptake and metabolomics approaches, we highlight intestinal organoids as robust and reliable tool in this field of research. Currently used in vitro models to study intestinal nutrient absorption, drug transport and enterocyte metabolism, such as Caco-2 cells or rodent explant models are of limited value due to their cancer and non-human origin, respectively. Particularly species differences result in poorly correlative data and findings obtained in these models cannot be extrapolated reliably to humans, as indicated by high failure rates in drug development pipelines. In contrast, human intestinal organoids represent a superior model of the intestinal epithelium and might help to implement the 3Rs (Reduction, Refinement and Replacement) principle in basic science as well as the preclinical and regulatory setup.

Mitochondrial Metabolism in the Intestinal Stem Cell Niche-Sensing and Signaling in Health and Disease.

Mitochondrial metabolism, dynamics, and stress responses in the intestinal stem cell niche play a pivotal role in regulating intestinal epithelial cell homeostasis, including self-renewal and differentiation. In addition, mitochondria are increasingly recognized for their involvement in sensing the metabolic environment and their capability of integrating host and microbial-derived signals. Gastrointestinal diseases such as inflammatory bowel diseases and colorectal cancer are characterized by alterations of intestinal stemness, the microbial milieu, and mitochondrial metabolism. Thus, mitochondrial function emerges at the interface of determining health and disease, and failure to adapt mitochondrial function to environmental cues potentially results in aberrant tissue responses. A mechanistic understanding of the underlying role of mitochondrial fitness in intestinal pathologies is still in its infancy, and therapies targeting mitochondrial (dys)function are currently lacking. This review discusses mitochondrial signaling and metabolism in intestinal stem cells and Paneth cells as critical junction translating host- and microbe-derived signals into epithelial responses. Consequently, we propose mitochondrial fitness as a hallmark for intestinal epithelial cell plasticity, determining the regenerative capacity of the epithelium.