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Patho-physiology of hepatic AQP9 in non-alcoholic liver disease (NAFLD), a common feature of metabolic syndrome
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Permeability transition pore, aquaporin-8 and mitochondrial water transport: news and views
No full textHepatic uptake of glycerol and Aquaporin-9 are altered in Non-Alcoholic Fatty Liver Disease
No full textNon-Alcoholic Fatty Liver Disease (NAFLD), a pathology caused by excessive accumulation of triglycerides (TG) within hepatocytes, is recognized as the leading cause of chronic liver disease in adults and children worldwide. NAFLD is often associated with obesity and diabetes and mostly closely linked to insulin resistance. Investigation into NAFLD pathogenesis has increased exponentially in the last years. Main pathways include increased visceral adipose tissue and insulin resistance, altered hepatic fatty acid export, oxidation, and desaturation within the liver, and the initiation and subsequent effects of lipotoxicity. Altered uptake of glycerol by hepatocytes is also a major intersecting component, however, the underlying mechanism has begun to be understood only recently after Aquaporin-9 (AQP9), an aquaglyceroporin regulated by insulin and leptin, was found to mediate liver glycerol permeability. AQP9 is dysregulated in the liver of morbidly obese patients with NAFLD associated with insulin resistance and diabetes and in animal models of NAFLD. The reduction in AQP9 expression and consequent decrease of glycerol influx into steatotic hepatocytes is hypothesized to be a compensatory mechanism to avoid further infiltration of TGs in liver parenchyma. Besides being a new important player in metabolic homeostasis AQP9 may prove a novel target to treat therapeutically NAFLD, a common feature of metabolic syndrome
The Escherichia coli Aquaporin-Z water channel
No full textThe membrane pathway of the rapid fluxes of water
by which microorganisms adapt promptly to abrupt
changes in environmental osmolality have begun to
be understood since the discovery of the Escherichia
coli aquaporin-Z water channel, AqpZ. As in animals
and plants, aquaporins are variously represented
among microorganisms, in which 31 homologous
genes have already been identified in eubacteria,
Archaea, fungi and protozoa. The AqpZ channel is
selectively permeable to water, although other functions
are not excluded. Consistent with a conservation
over the course of evolution, AqpZ and AQP1, a
human counterpart, share similar structures. The aqpZ
gene is growth phase and osmotically regulated.
AqpZ has a role in both the short- and the long-term
osmoregulatory response and is required by rapidly
growing cells. AqpZ-like proteins seem to be necessary
for the virulence expressed by some pathogenic
bacteria. Microbial aquaporins are also likely to be
involved in spore formation and/or germination. Additional
roles may still be unknown. The use of AqpZ as
a model system will continue to provide insight into
the understanding of the importance of aquaporins
Understanding microbial MIP channels
No full textThe microbial members of the MIP
family of transmembrane channel
proteins are attracting considerable
interest, and a topical review of their
structural and biological features was
provided recently by Hohmann et al.1
MIP proteins are widely distributed
throughout nature. Already, 220
MIP family members, including 74 of
microbial origin, have been identified
and partially characterized; many
more will be identified as a result of
genome sequencing. In spite of their
2.5–3 billion years of evolutionary
history, microbial MIP proteins
are structurally similar to their
invertebrate and vertebrate
counterparts2. However, unlike MIP
proteins from higher organisms, the
linear sequences of which permit us
to distinguish homologues highly
selective for water (aquaporins, AQP)
and homologues permeable to
glycerol and other small neutral
solutes in addition to water
(aquaglyceroporins3), the correlation
between sequence and functional
properties of microbial MIPs has
not yet been fully assessed
The microbial Escherichia coli Aquaporin-Z water channel. Structural, functional and physiological properties
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