Supplementary Material for: Catecholamine Metabolism Induces Mitochondrial DNA Deletions and Leads to Severe Adrenal Degeneration during Aging

<p><b><i>Background:</i></b> Aging is a multifactorial process characterized by organ loss of function and degeneration, but the mechanisms involved remain elusive. We have shown recently that catecholamine metabolism drives the accumulation of mitochondrial DNA (mtDNA) deletions in dopaminergic cells, which likely contribute to their degeneration during aging. Here we investigated whether the well-documented degeneration and altered function of adrenals during aging is linked to catecholamine production in the medulla followed by accumulation of mtDNA deletions. <b><i>Material and Methods:</i></b> We analyzed adrenal medullary and cortical samples of both murine and human origin covering a wide range of ages for mtDNA deletion content, mtDNA copy number, mitochondrial and cellular integrity as well as aging-related tissue changes such as fibrosis. <b><i>Results:</i></b> Indeed, we demonstrate in mice and humans that the adrenal medulla accumulates a strikingly high amount of mtDNA deletions with age, causing mitochondrial dysfunction in the adrenal medulla, but also in the cortex, accompanied by apoptosis and, more importantly, by severe inflammation and remarkable fibrosis. Additionally, a concomitant and dramatic loss of medullary and cortical cells is observed in old animals. <b><i>Conclusion:</i></b> Our results show that accumulation of mtDNA deletions, and the ensuing mitochondrial dysfunction, is a hallmark of adrenal aging, further strengthening the hypothesis that catecholamine metabolism is detrimental to mtDNA integrity, mitochondrial function and cell survival. Moreover, the cell loss potentially induced by mitochondrial dysfunction could explain the decline in adrenal hormonal and steroidal secretion during aging.</p

Mitochondrial function in murine skin epithelium is crucial for hair follicle morphogenesis and epithelial-mesenchymal interactions

NoHere, we studied how epithelial energy metabolism impacts overall skin development by selectively deleting intraepithelial mtDNA in mice by ablating a key maintenance factor (TfamEKO), which induces loss of function of the electron transport chain (ETC). Quantitative (immuno)histomorphometry demonstrated that TfamEKO mice showed significantly reduced hair follicle (HF) density and morphogenesis, fewer intrafollicular keratin15+ epithelial progenitor cells, increased apoptosis, and reduced proliferation. TfamEKO mice also displayed premature entry into (aborted) HF cycling by apoptosis-driven HF regression (catagen). Ultrastructurally, TfamEKO mice exhibited severe HF dystrophy, pigmentary abnormalities, and telogen-like condensed dermal papillae. Epithelial HF progenitor cell differentiation (Plet1, Lrig1 Lef1, and β-catenin), sebaceous gland development (adipophilin, Scd1, and oil red), and key mediators/markers of epithelial–mesenchymal interactions during skin morphogenesis (NCAM, versican, and alkaline phosphatase) were all severely altered in TfamEKO mice. Moreover, the number of mast cells, major histocompatibility complex class II+, or CD11b+ immunocytes in the skin mesenchyme was increased, and essentially no subcutis developed. Therefore, in contrast to their epidermal counterparts, pilosebaceous unit stem cells depend on a functional ETC. Most importantly, our findings point toward a frontier in skin biology: the coupling of HF keratinocyte mitochondrial function with the epithelial–mesenchymal interactions that drive overall development of the skin and its appendages

The Mitochondrial Electron Transport Chain Is Dispensable for Proliferation and Differentiation of Epidermal Progenitor Cells.

noTissue stem cells and germ line or embryonic stem cells were shown to have reduced oxidative metabolism, which was proposed to be an adaptive mechanism to reduce damage accumulation caused by reactive oxygen species. However, an alternate explanation is that stem cells are less dependent on specialized cytoplasmic functions compared with differentiated cells, therefore, having a high nuclear-to-cytoplasmic volume ratio and consequently a low mitochondrial content. To determine whether stem cells rely or not on mitochondrial respiration, we selectively ablated the electron transport chain in the basal layer of the epidermis, which includes the epidermal progenitor/stem cells (EPSCs). This was achieved using a loxP-flanked mitochondrial transcription factor A (Tfam) allele in conjunction with a keratin 14 Cre transgene. The epidermis of these animals (TfamEKO) showed a profound depletion of mitochondrial DNA and complete absence of respiratory chain complexes. However, despite a short lifespan due to malnutrition, epidermal development and skin barrier function were not impaired. Differentiation of epidermal layers was normal and no proliferation defect or major increase of apoptosis could be observed. In contrast, mice with an epidermal ablation of prohibitin-2, a scaffold protein in the inner mitochondrial membrane, displayed a dramatic phenotype observable already in utero, with severely impaired skin architecture and barrier function, ultimately causing death from dehydration shortly after birth. In conclusion, we here provide unequivocal evidence that EPSCs, and probably tissue stem cells in general, are independent of the mitochondrial respiratory chain, but still require a functional dynamic mitochondrial compartment