The Role of the Mitochondria in the Evolution of Stem Cells, Including MUSE Stem Cells and Their Biology

On the potential origin and characteristics of cancer stem cells

The 'cancer stem cell' hypothesis has pointed to a specific target for new cancer therapies. The hypothesis is based on the observation that only the 'cancer stem cell' among the other heterogeneous cancer cells can sustain the growth of the cancer. The goal is to identify biomarkers of 'cancer stem cells' to distinguish them from the 'cancer non-stem cells' and normal adult tissue-specific stem cells. This analyst posits a hypothesis that, although all cancers originated from a single cell, there exist two types of 'cancer stem cells' either by the 'Stem Cell hypothesis' or from the 'De-differentiation hypothesis'. It is proposed that there exist two different 'cancer stem cells'. Some 'cancer stem cells' (a) lack the expression of connexins or gap junction genes and lack any form of gap junctional intercellular communication (GJIC) or (b) they have the expressed connexin-coded proteins for functional GJIC but are dysfunctional by some expressed oncogene. This is consistent with the Loewenstein hypothesis that a universal characteristic of cancer cells is they do not have growth control, nor terminally differentiate. This review speculates the normal organ-specific adult stem cell, that is 'initiated', is the origin of the 'cancer stem cells' with expressed Oct4A gene and no expressed connexin genes; whereas the other cancer stem cell has no expressed Oct4A genes but expressed connexin gene, whose coded protein is dysfunctional. Hence. both types of 'cancer stem cells' lack GJIC, for two different reasons, the selective therapies have to be different for these different cell types.

Output Regulation and Function Optimization of Mitochondria in Eukaryotes

The emergence of endosymbiosis between aerobic alpha-proteobacterium and anaerobic eukaryotic cell precursors opened the chapter of eukaryotic evolution. Multiple functions of mitochondria originated from the ancient precursors of mitochondria and underwent remodeling in eukaryotic cells. Due to the dependence on mitochondrial functions, eukaryotic cells need to constantly adjust mitochondrial output based on energy demand and cellular stress. Meanwhile, eukaryotes conduct the metabolic cooperation between different cells through the involvement of mitochondria. Under some conditions, mitochondria might also be transferred to nearby cells to provide a protective mechanism. However, the endosymbiont relationship determines the existence of various types of mitochondrial injury, such as proteotoxic stress, mutational meltdown, oxidative injure, and immune activation caused by released mitochondrial contents. Eukaryotes have a repertoire of mitochondrial optimization processes, including various mitochondrial quality-control proteins, regulation of mitochondrial dynamics and activation of mitochondrial autophagy. When these quality-control processes fail, eukaryotic cells can activate apoptosis to intercept uncontrolled cell death, thereby minimizing the damage to extracellular tissue. In this review, we describe the intracellular and extracellular context-based regulation of mitochondrial output in eukaryotic cells, and introduce new findings on multifaceted quality-control processes to deal with mitochondrial defects.

Effects of Diesel Exhaust Particles on Mouse Gastric Stem Cells

Stem cells have attracted many scientists because of their unique properties and therapeutic applications. However, very little is known on the environmental toxins that could affect their biological features. This study focuses on the consequences of the exposure of a cell line representative of the mouse gastric stem/progenitor (mGS) cells to diesel exhaust particles (DEPs). These immortal cells were cultured using routine protocols. The DEPs were added to the culture media at 1, 10, and 100 µg/mL for 1 to 72 h. The cells were assayed for their viability, migration, oxidative stress, and the expression of genes specific for cell proliferation, pluripotency, and death. DEPs induced a reduction in the metabolic activity of mGS cells, only at a high concentration of 100 µg/mL. However, no significant effects were detected on cell migration, oxidative stress markers (glutathione and thiobarbituric acid reactive substances), and cell death related proteins/genes. Interestingly, these findings were associated with down-regulation of Notch 2 and 3 and Bmi-1 proteins and activation of STAT3 involved in the regulation of the fate of stem cells. In conclusion, this study demonstrates that mGS cells have some resistance to oxidative stress and apoptosis when exposed to DEPs at the expense of their stemness.