More than 40 human diseases are associated with fibrillar deposits of specific peptides or proteins in tissue. Amyloid fibrils, or their precursors, can be highly toxic to cells, suggesting their key role in disease pathogenesis. Proteins not associated with any disease are able to form oligomers and amyloid assemblies in vitro displaying structures and cytotoxicity comparable with those of aggregates of diseaserelated polypeptides. In isolated cells, such toxicity has been shown to result from increased membrane permeability with disruption of ion homeostasis and oxidative stress. Here we microinjected into the nucleus basalis magnocellularis of rat brains aggregates of an Src homology 3 domain and the N-terminal domain of the prokaryotic HypF, neither of which is associated with amyloid disease. Prefibrillar aggregates of both proteins, but not their mature fibrils or soluble monomers, impaired cholinergic neuron viability in a dose-dependent manner similar to that seen in cell cultures. Contrary to the situation with cultured cells, however, under our experimental conditions, cell stress in tissue is not followed by a comparable level of cell death, a result that is very likely to reflect the presence of protective mechanisms reducing aggregate toxicity. These findings support the hypothesis that neurodegenerative disorders result primarily from a generic cell dysfunction caused by early misfolded species in the aggregation process.

Metabolic pathologies mainly originate from adipose tissue (AT) dysfunctions. AT differences are associated with fat-depot anatomic distribution in subcutaneous (SAT) and visceral omental (VAT) pads. We address the question whether the functional differences between the two compartments may be present early in the adipose stem cell (ASC) instead of being restricted to the mature adipocytes. Using a specific human ASC model, we evaluated proliferation/differentiation of ASC from abdominal SAT-(S-ASC) and VAT-(V-ASC) paired biopsies in parallel as well as the electrophysiological properties and functional activity of ASC and their in vitro-derived adipocytes. A dramatic difference in proliferation and adipogenic potential was observed between the two ASC populations, S-ASC having a growth rate and adipogenic potential significantly higher than V-ASC and giving rise to more functional and better organized adipocytes. To our knowledge, this is the first comprehensive electrophysiological analysis of ASC and derived-adipocytes, showing electrophysiological properties, such as membrane potential, capacitance and K+-current parameters which confirm the better functionality of S-ASC and their derived adipocytes. We document the greater ability of S-ASC-derived adipocytes to secrete adiponectin and their reduced susceptibility to lipolysis. These features may account for the metabolic differences observed between the SAT and VAT. Our findings suggest that VAT and SAT functional differences originate at the level of the adult ASC which maintains a memory of its fat pad of origin. Such stem cell differences may account for differential adipose depot susceptibility to the development of metabolic dysfunction and may represent a suitable target for specific therapeutic approaches.

Adipose tissue is a dynamic endocrine organ with a central role in metabolism regulation. Functional differences in adipose tissue seem associated with the regional distribution of fat depots, in particular in subcutaneous and visceral omental pads. Here, we report for the first time the isolation of human adipose-derived adult stem cells from visceral omental and subcutaneous fat (V-ASCs and S-ASCs, respectively) from the same subject. Immunophenotyping shows that plastic culturing selects homogeneous cell populations of V-ASCs and S-ASCs from the corresponding stromal vascular fractions (SVFs), sharing typical markers of mesenchymal stem cells. Electron microscopy and electrophysiological and real-time RT-PCR analyses confirm the mesenchymal stem nature of both V-ASCs and S-ASCs, while no significant differences in a limited pattern of cytokine/chemokine expression can be detected. Similar to S-ASCs, V-ASCs can differentiate in vitro toward adipogenic, osteogenic, chondrogenic, muscular, and neuronal lineages, as demonstrated by histochemical, immunofluorescence, real-time RT-PCR, and electrophysiological analyses, suggesting the multipotency of such adult stem cells. Our data demonstrate that both visceral and subcutaneous adipose tissues are a source of pluripotent stem cells with multigermline potential. However, the visceral rather than the subcutaneous ASC could represent a more appropriate in vitro cell model for investigating the molecular mechanisms implicated in the pathophysiology of metabolic disorders such as obesity.

It has been reported that different tissue or cultured cell types are variously affected by the exposure to toxic protein aggregates, however a substantial lack of information exists about the biochemical basis of cell resistance or susceptibility to the aggregates. We investigated the extent of the cytotoxic effects elicited by supplementing the media of a panel of cultured cell lines with aggregates of HypF-N, a prokaryotic domain not associated with any amyloid disease. The cell types exposed to early, pre-fibrillar aggregates (not mature fibrils) displayed variable susceptibility to damage and to apoptotic death with a significant inverse relation to membrane content in cholesterol. Susceptibility to damage by the aggregates was also found to be significantly related to the ability of cells to counteract early modifications of the intracellular free Ca2+ and redox status. Accordingly, cell resistance appeared related to the efficiency of the biochemical equipment leading any cell line to sustain the activity of Ca2+ pumps while maintaining under control the oxidative stress associated with the increased metabolic rate. Our data depict membrane destabilization and the subsequent early derangement of ion balance and intracellular redox status as key events in targeting exposed cells to apoptotic death.