Summary: The Escherichia coli ompA mRNA, encoding a highly abundant outer membrane protein, has served as a model for regulated mRNA decay in bacteria. The half‐life of this transcript correlates inversely with the bacterial growth rate and is growth stage‐dependent. The stability of the messenger is determined by the 5′‐untranslated region which possesses cleavage sites for RNase E. Hfq binds to this region, is essential for controlling the stability and has been suggested to directly regulate ompA mRNA decay. Here we report that the 78 nucleotide SraD RNA, which is highly conserved among Enterobacteriaceae, acts in destabilizing the ompA transcript when rapidly grown cells enter the stationary phase of growth. During this growth‐stage the expression of SraD RNA becomes strongly increased. The SraD‐mediated decay of ompA mRNA depends on Hfq and in vitro studies revealed that Hfq facilitates binding of the regulatory RNA to the translational initiation region of the messenger. Deletion of sraD, however, does not significantly affect the stability of the ompA mRNA in slowly growing cells. Our results indicate that distinct regulatory circuits are responsible for growth phase‐ and growth rate‐dependent control of the ompA mRNA stability.

Two new globin proteins have recently been discovered in vertebrates, neuroglobin in neurons and cytoglobin in all tissues, both showing heme hexacoordination by the distal His(E7) in the absence of gaseous ligands. In analogy to hemoglobin and myoglobin, neuroglobin and cytoglobin are supposedly involved in O₂ storage and delivery, although their physiological role remains to be solved. Here we report O₂ equilibria of recombinant human neuroglobin (NGB) and cytoglobin (CYGB) measured under close to physiological conditions and at varying temperature and pH ranges. NGB shows both alkaline and acid Bohr effects (pH-dependent O₂ affinity) and temperature-dependent enthalpy of oxygenation. O₂ and CO binding equilibrium studies on neuroglobin mutants strongly suggest that the bound O₂ is stabilized by interactions with His(E7) and that this residue functions as a major Bohr group in the presence of Lys(E10). As shown by the titration of free thiols with 4,4′-dithiodipyridine and by mass spectrometry, this mechanism of modulating O₂ affinity is independent of formation of an internal disulfide bond under the experimental conditions used, which stabilize thiols in the reduced form. In CYGB, O₂ binding is cooperative, consistent with its proposed dimeric structure. Similar to myoglobin but in contrast to NGB, O₂ binding to CYGB is pH-independent and exothermic throughout the temperature range investigated. Our data support the hypothesis that CYGB may be involved in O₂-requiring metabolic processes. In contrast, the lower O₂ affinity in NGB does not appear compatible with a physiological role involving mitochondrial O₂ supply at the low O₂ tensions found within neurons.

The field of cell therapy and regenerative medicine can hold the promise of restoring normal tissues structure and function. Additionally, the main targets of stem cell-based therapies are chronic diseases and lifelong disabilities without definite cures such as osteoporosis. Osteoporosis as one of the important causes of morbidity in older men and post-menopausal women is characterized by reduced bone quantity or skeletal tissue atrophy that leads to an increased risk of osteoporotic fractures. The common therapeutic methods for osteoporosis only can prevent the loss of bone mass and recover the bone partially. Nevertheless, stem cell-based therapy is considered as a new approach to regenerate the bone tissue. Herein, mesenchymal stem cells as pivotal candidates for regenerative medicine purposes especially bone regeneration are the most common type of cells with anti-inflammatory, immune-privileged potential, and less ethical concerns than other types of stem cells which are investigated in osteoporosis. Based on several findings, the mesenchymal stem cells effectiveness near to a great extent depends on their secretory function. Indeed, they can be involved in the establishment of normal bone remodeling via initiation of specific molecular signaling pathways. Accordingly, the aim herein was to review the effects of stem cell-based therapies in osteoporosis.

The presence of DPPII (dipeptidyl peptidase II; E.C. 3.4.14.2) has been demonstrated in various mammalian tissues. However, a profound molecular and catalytic characterization, including substrate selectivity, kinetics and pH-dependence, has not been conducted. In the present study, DPPII was purified from human seminal plasma to apparent homogeneity with a high yield (40%) purification scheme, including an inhibitor-based affinity chromatographic step. The inhibitor lysyl-piperidide (Ki~0.9 μM at pH 5.5) was chosen, as it provided a favourable affinity/recovery ratio. The human enzyme appeared as a 120 kDa homodimer. Mass spectrometric analysis after tryptic digestion together with a kinetic comparison indicate strongly its identity with QPP (quiescent cell proline dipeptidase), also called dipeptidyl peptidase 7. pH profiles of both kcat and kcat/Km clearly demonstrated that DPPII/QPP possesses an acidic and not a neutral optimum as was reported for QPP. Kinetic parameters of the human natural DPPII for dipeptide-derived chromogenic [pNA (p-nitroanilide)] and fluorogenic [4Me2NA (4-methoxy-2-naphthylamide)] substrates were determined under different assay conditions. DPPII preferred the chromogenic pNA-derived substrates over the fluorogenic 4Me2NA-derived substrates. Natural human DPPII showed high efficiency towards synthetic substrates containing proline at the P1 position and lysine at P2. The importance of the P1′ group for P2 and P1 selectivity was revealed, explaining many discrepancies in the literature. Furthermore, substrate preferences of human DPPII and dipeptidyl peptidase IV were compared based on their selectivity constants (kcat/Km). Lys-Pro-pNA (kcat/Km 4.1×106 s−1·M−1) and Ala-Pro-pNA (kcat/Km 2.6×106 s−1· M−1) were found to be the most sensitive chromogenic substrates for human DPPII, but were less selective than Lys-Ala-pNA (kcat/Km 0.4×106 s−1·M−1).