An information theoretic approach to insulin sensing by human kidney podocytes.

Podocytes are key components of the glomerular filtration barrier (GFB). They are insulin-responsive but can become insulin-resistant, causing features of the leading global cause of kidney failure, diabetic nephropathy. Insulin acts via insulin receptors to control activities fundamental to GFB integrity, but the amount of information transferred is unknown.

Autophagy facilitates organelle clearance during differentiation of human erythroblasts: evidence for a role for ATG4 paralogs during autophagosome maturation.

Wholesale depletion of membrane organelles and extrusion of the nucleus are hallmarks of mammalian erythropoiesis. Using quantitative EM and fluorescence imaging we have investigated how autophagy contributes to organelle removal in an ex vivo model of human erythroid differentiation. We found that autophagy is induced at the polychromatic erythroid stage, and that autophagosomes remain abundant until enucleation.

The ins and outs of human reticulocyte maturation: autophagy and the endosome/exosome pathway.

The maturation of reticulocytes into functional erythrocytes is a complex process requiring extensive cytoplasmic and plasma membrane remodeling, cytoskeletal rearrangements and changes to cellular architecture. Autophagy is implicated in the sequential removal of erythroid organelles during erythropoiesis, although how this is regulated during late stages of erythroid differentiation, and the potential contribution of autophagy during reticulocyte maturation, remain unclear. Using an optimized ex vivo differentiation system for human erythropoiesis, we have observed that maturing reticulocytes are characterized by the presence of one or few large vacuolar compartments.

Maturing reticulocytes internalize plasma membrane in glycophorin A-containing vesicles that fuse with autophagosomes before exocytosis.

The erythrocyte is one of the best characterized human cells. However, studies of the process whereby human reticulocytes mature to erythrocytes have been hampered by the difficulty of obtaining sufficient numbers of cells for analysis. In the present study, we describe an in vitro culture system producing milliliter quantities of functional mature human adult reticulocytes from peripheral blood CD34(+) cells.

A cryptic mitochondrial targeting motif in Atg4D links caspase cleavage with mitochondrial import and oxidative stress.

The Atg4 cysteine proteases play crucial roles in the processing of Atg8 proteins during autophagy, but their regulation during cellular stress and differentiation remains poorly understood. We have found that two Atg4 family members--Atg4C and Atg4D--contain cryptic mitochondrial targeting sequences immediately downstream of their canonical (DEVD) caspase cleavage sites. Consequently, caspase-cleaved Atg4D (ΔN63 Atg4D) localizes to the mitochondrial matrix when expressed in mammalian cells, where it undergoes further processing to a ~42 kDa mitochondrial form.

Atg4D at the interface between autophagy and apoptosis.

The Atg4 family of endopeptidases regulates autophagosome biogenesis by priming newly synthesized Atg8 to enable covalent attachment of phosphatidylethanolamine, and by delipidating Atg8 at the lysosomal fusion step. Control of Atg4 activity is therefore crucial, although little is known about how these molecules are regulated in living cells. We have found that one human Atg4 family member (Atg4D) is cleaved at DEVD(63)K by caspase-3 during apoptosis.

Caspase cleavage of Atg4D stimulates GABARAP-L1 processing and triggers mitochondrial targeting and apoptosis.

Autophagy is an important catabolic process with roles in cell survival and cell death. It sequesters cytosol and organelles within double-membrane autophagosomes that deliver their contents to lysosomes for degradation. Autophagosome biogenesis is coordinated by the autophagy-related protein 4 (Atg4) family of C54 endopeptidases (Atg4A-Atg4D).

A novel role for microtubules in apoptotic chromatin dynamics and cellular fragmentation.

Dramatic changes in cellular dynamics characterise the apoptotic execution phase, culminating in fragmentation into membrane-bound apoptotic bodies. Previous evidence suggests that actin-myosin plays a dominant role in apoptotic cellular remodelling, whereas all other cytoskeletal elements dismantle. We have used fixed cells and live-cell imaging to confirm that interphase microtubules rapidly depolymerise at the start of the execution phase.

Is puberty an accelerator of type 1 diabetes in IL6-174CC females?

The pubertal peak in onset of type 1 diabetes occurs earlier in girls than boys. We postulated that this sex difference might be mediated in part by estrogen or by genes regulated by estrogen, such as the interleukin-6 (IL6) gene. Previous studies concerning the role of an estrogen-sensitive single nucleotide polymorphism (SNP) in the IL6 promoter in type 1 diabetes have proved contradictory.