Hsp70 and Hsp40 inhibit an inter-domain interaction necessary for transcriptional activity in the androgen receptor.

Molecular chaperones such as Hsp40 and Hsp70 hold the androgen receptor (AR) in an inactive conformation. They are released in the presence of androgens, enabling transactivation and causing the receptor to become aggregation-prone. Here we show that these molecular chaperones recognize a region of the AR N-terminal domain (NTD), including a FQNLF motif, that interacts with the AR ligand-binding domain (LBD) upon activation. This suggests that competition between molecular chaperones and the LBD for the FQNLF motif regulates AR activation. We also show that, while the free NTD oligomerizes, binding to Hsp70 increases its solubility. Stabilizing the NTD-Hsp70 interaction with small molecules reduces AR aggregation and promotes its degradation in cellular and mouse models of the neuromuscular disorder spinal bulbar muscular atrophy. These results help resolve the mechanisms by which molecular chaperones regulate the balance between AR aggregation, activation and quality control

Diaphragm Muscle Weakness in an Experimental Porcine Intensive Care Unit Model

In critically ill patients, mechanisms underlying diaphragm muscle remodeling and resultant dysfunction contributing to weaning failure remain unclear. Ventilator-induced modifications as well as sepsis and administration of pharmacological agents such as corticosteroids and neuromuscular blocking agents may be involved. Thus, the objective of the present study was to examine how sepsis, systemic corticosteroid treatment (CS) and neuromuscular blocking agent administration (NMBA) aggravate ventilator-related diaphragm cell and molecular dysfunction in the intensive care unit. Piglets were exposed to different combinations of mechanical ventilation and sedation, endotoxin-induced sepsis, CS and NMBA for five days and compared with sham-operated control animals. On day 5, diaphragm muscle fibre structure (myosin heavy chain isoform proportion, cross-sectional area and contractile protein content) did not differ from controls in any of the mechanically ventilated animals. However, a decrease in single fibre maximal force normalized to cross-sectional area (specific force) was observed in all experimental piglets. Therefore, exposure to mechanical ventilation and sedation for five days has a key negative impact on diaphragm contractile function despite a preservation of muscle structure. Post-translational modifications of contractile proteins are forwarded as one probable underlying mechanism. Unexpectedly, sepsis, CS or NMBA have no significant additive effects, suggesting that mechanical ventilation and sedation are the triggering factors leading to diaphragm weakness in the intensive care unit

Fibre structure and function.

<p>[A] Number of fibres tested. [B] Cross-sectional area (CSA). [C] Maximal force production normalized to CSA (P₀/CSA). [D] Stiffness (E₀). [E] Fraction of strongly attached cross-bridges (α_fs). [F] Apparent rate constant of force redevelopment (k_tr). Values from CTL (white), MV (red bars), NMBA (green), CS (yellow), sepsis (blue) and ALL groups (black) appear. Data are presented as means.</p

Protein and gene expressions.

<p>[A] MyHC isoform composition. [B] Contractile protein content. [C] Total protein over fibre volume. [D] mRNA levels of contractile proteins. Values from sham-operated control piglets (CTL group, white bars) and animals that were mechanically ventilated (MV group, red bars), mechanically ventilated with a neuromuscular blocking agent administration (NMBA group, green bars), mechanically ventilated with corticosteroid administration (CS group, yellow bars), mechanically ventilated with an injection of a endotoxin-induced sepsis (sepsis group, blue bars) and mechanically ventilated with a combination of endotoxin-induced sepsis, CS and NMBA (ALL group, black bars) for five days. Data are presented as means ± SEMs. Asterisk denotes a statistically significant difference compared with CTL (p<0.05).</p

Contractile protein reactive carbonyl derivatives.

<p>[A] CTL (white bars), MV (red bars), NMBA (green bars), CS (yellow bars), sepsis (blue bars) and ALL groups (black bars). [B] Typical western blot showing reactive carbonyl derivates for various piglets. Data are presented as means ± SEMs. Asterisk denotes a statistically significant difference compared with CTL (p<0.05).</p