Oxygen-sensitive accumulation and degradation, two opposite but intrinsically linked events, of heme proteins in mitochondria affect mitochondrial functions, including bioenergetics and oxygen-sensing processes. Cystathionine β-synthase (CBS) contains a prosthetic heme group and catalyzes the production of hydrogen sulfide in mammalian cells. Here we show that CBS proteins were present in liver mitochondria at a low level under normoxia conditions. Ischemia/hypoxia increased the accumulation of CBS proteins in mitochondria. The normalization of oxygen partial pressure accelerated the degradation of CBS proteins. Lon protease, a major degradation enzyme in mitochondrial matrix, recognized and degraded mitochondrial CBS by specifically targeting at the oxygenated heme group of CBS proteins. The accumulation of CBS in mitochondria increased hydrogen sulfide production, which prevented Ca 2+ -mediated cytochrome c release from mitochondria and decreased reactive oxygen species generation. Mitochondrial accumulation of heme oxygenase-1, another heme protein, was also regulated by oxygen level and Lon protease in the same mechanism as for CBS. Our findings provide a fundamental and general mechanism for oxygen-sensitive regulation of mitochondrial functions by linking oxygenation level to the accumulation/ degradation of mitochondrial heme proteins.gasotransmitter | hepatocytes | mitochondrial swelling | signaling | transfection M itochondrial protein quality control system maintains homeostasis of mitochondria via regulated mitochondrial biogenesis and protein degradation (1, 2). Lon protease is a major protease in mitochondrial matrix in mammalian cells, being engaged in the degradation of proteins to prevent protein aggregation (2, 3). In doing so, Lon protease regulates many oxygen/ATP-dependent mitochondrial processes under physiological and pathophysiological conditions, such as DNA binding, chaperone activity, the assembly of respiratory complexes, and cellular aging and degeneration.Mitochondrial heme-containing proteins are indispensable for normal mitochondrial function such as oxidative phosphorylation and biogenesis. The mechanisms by which Lon protease recognizes and regulates the degradation of mitochondrial heme proteins are unknown to date. Cystathionine β-synthase (CBS) is a nuclear encoding heme protein, playing a key role in homocysteine and cysteine metabolism and endogenous H 2 S production (4-6). Deficiency of CBS as seen in autosomal recessively genetic disease causes homocystinuria, leading to dislocated optic lenses, skeletal disorders, mental retardation, and vascular disorders (4-6). As a gasotransmitter, H 2 S regulates a wide variety of physiological events from vasorelaxation to glucose metabolism (4,7,8). We hypothesize that the presence and accumulation of CBS in mammalian mitochondria are regulated by an interaction of the heme group and oxygen molecule and this interaction is under the control of Lon protease. A better understanding of whether and how CBS in mammalian mitochondria is ...

The Polycomb group (PcG) proteins have an important role in controlling the expression of key genes implicated in embryonic development, differentiation, and decision of cell fates. Emerging evidence suggests that Polycomb repressive complexes 1 (PRC1) is defined by the six Polycomb group RING finger protein (Pcgf) paralogs, and Pcgf proteins can assemble into noncanonical PRC1 complexes. However, little is known about the precise mechanisms of differently composed noncanonical PRC1 in the maintenance of the pluripotent cell state. Here we disrupt the Pcgf genes in mouse embryonic stem cells by CRISPR-Cas9 and find Pcgf6 null embryonic stem cells display severe defects in self-renewal and differentiation. Furthermore, Pcgf6 regulates genes mostly involved in differentiation and spermatogenesis by assembling a noncanonical PRC1 complex PRC1.6. Notably, Pcgf6 deletion causes a dramatic decrease in PRC1.6 binding to target genes and no loss of H2AK119ub1. Thus, Pcgf6 is essential for recruitment of PRC1.6 to chromatin. Our results reveal a previously uncharacterized, H2AK119ub1-independent chromatin assembly associated with PRC1.6 complex.

Three-dimensional (3D) printing is a rapidly emerging technology that promises to transform tissue engineering into a commercially successful biomedical industry. However, the use of robotic bioprinters alone is not sufficient for disease treatment. This study aimed to report the combined application of 3D scanning and 3D printing for treating bone and cartilage defects. Three different kinds of defect models were created to mimic three orthopedic diseases: large segmental defects of long bones, free-form fracture of femoral condyle, and International Cartilage Repair Society grade IV chondral lesion. Feasibility of in situ 3D bioprinting for these diseases was explored. The 3D digital models of samples with defects and corresponding healthy parts were obtained using high-resolution 3D scanning. The Boolean operation was used to achieve the shape of the defects, and then the target geometries were imported in a 3D bioprinter. Two kinds of photopolymerized hydrogels were synthesized as bioinks. Finally, the defects of bone and cartilage were restored perfectly in situ using 3D bioprinting. The results of this study suggested that 3D scanning and 3D bioprinting could provide another strategy for tissue engineering and regenerative medicine.