Why the impact of mechanical stimuli on stem cells remains a challenge

Mechanical stimulation affects growth and differentiation of stem cells. This may be used to guide lineage-specific cell fate decisions and therefore opens fascinating opportunities for stem cell biology and regenerative medicine. Several studies demonstrated functional and molecular effects of mechanical stimulation but on first sight these results often appear to be inconsistent. Comparison of such studies is hampered by a multitude of relevant parameters that act in concert. There are notorious differences between species, cell types, and culture conditions. Furthermore, the utilized culture substrates have complex features, such as surface chemistry, elasticity, and topography. Cell culture substrates can vary from simple, flat materials to complex 3D scaffolds. Last but not least, mechanical forces can be applied with different frequency, amplitude, and strength. It is therefore a prerequisite to take all these parameters into consideration when ascribing their specific functional relevance—and to only modulate one parameter at the time if the relevance of this parameter is addressed. Such research questions can only be investigated by interdisciplinary cooperation. In this review, we focus particularly on mesenchymal stem cells and pluripotent stem cells to discuss relevant parameters that contribute to the kaleidoscope of mechanical stimulation of stem cells.     

Tom22 is a multifunctional organizer of the mitochondrial preprotein translocase.

Mitochondrial preproteins are imported by a multisubunit translocase of the outer membrane (TOM), including receptor proteins and a general import pore. The central receptor Tom22 binds preproteins through both its cytosolic domain and its intermembrane space domain and is stably associated with the channel protein Tom40 (refs 11-13). Here we report the unexpected observation that a yeast strain can survive without Tom22, although it is strongly reduced in growth and the import of mitochondrial proteins. Tom22 is a multifunctional protein that is required for the higher-level organization of the TOM machinery. In the absence of Tom22, the translocase dissociates into core complexes, representing the basic import units, but lacks a tight control of channel gating. The single membrane anchor of Tom22 is required for a stable interaction between the core complexes, whereas its cytosolic domain serves as docking point for the peripheral receptors Tom20 and Tom70. Thus a preprotein translocase can combine receptor functions with distinct organizing roles in a multidomain protein.     

Effects of temperature on the responses to noradrenaline, isoprenaline and histamine on isolated rabbit mesenteric artery.

On the rabbit mesenteric artery, the elevation of temperature from 25 degrees up to 42 degrees diminished the affinity of histamine, whereas that of noradrenaline to the alpha-adrenoceptors remained unchanged. The presence of beta-adrenoceptors could not be demonstrated.     

Catecholamines in adult iron deficiency patients.

Patients with iron deficiency whether uncomplicated or associated with other types of anemias, had plasma catecholamine levels which were significantly increased above normal controls. Patients with a variety of other anemias had no significant increase in catecholamine levels. Plasma catecholamine levels in uncomplicated iron deficient patients approached normal values as early as 3 h following oral FeSO4.     

Die Cholesterin-7α-Hydroxylase-Aktivität der Rattenleber nach Hypophysektomie und nach Substitution mit Hypophysenhormonen

Summary In order to elucidate the role of the hypophysis in the regulation of cholesterol 7-hydroxylase activity, male and female rats hypophysectomized on day 50 of life were treated with different hypophyseal hormones and tested on day 85 of life. Only a crude extract from human hypophysis and ovine prolactin was able to enhance the enzyme activity, thereby restoring the level of intact controls.

---

---

Diese Arbeit wurde im Rahmen des Sonderforschungsbereiches Endokrinologie (SFB 87) von der Deutschen Forschungsgemeinschaft gefördert.     

Effects on prostaglandins F2α, I2, and indomethacin on isolated coronary arteries from healthy and alloxandiabetic dogs

Summary Contractile responses of isolated coronary arteries from healthy and alloxan-diabetic dogs to prostaglandin F₂ were enhanced by indomethacin and inhibited by prostaglandin I₂. The potentiation by indomethacin was more prominent in diabetic vessels than in normal arteries.