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Mitochondrial malfunction appears to be intimately associated with age and age-related complex disorders but the precise pathological relevance of such malfunction remains unclear. Mitochondrial, and more specifically bioenergetic, malfunction is commonly encountered in cancer, degenerative disorders and aging. The identification of a mitochondrial-nuclear retrograde signaling pathway in yeast has facilitated the study of the corresponding retrograde signaling mechanisms induced in response to mitochondrial malfunction in mammals including human. Mitochondrial-nuclear crosstalk is critical for the maintenance of cellular homeostasis, and some mitochondrial DNA mutations may perturb crosstalk signaling. However, ascertaining whether mitochondrial malfunction is a cause or a consequence of disease development will be key to determining whether or not impaired crosstalk signaling is of direct pathological and hence therapeutic relevance. Here, we review what is known about the nuclear adaptive compensatory mechanisms induced in response to mitochondrial malfunction. We discuss the role of mitochondrial DNA variants in modulating the penetrance of human inherited disease caused by mutations in the nuclear genome and explore the underlying mechanisms by which they influence the retrograde response. We conclude that mitochondrial DNA variants have the potential to induce molecular signals through the mitochondrial-nuclear crosstalk mechanism, thereby promoting nuclear compensation in response to mitochondrial malfunction. The implications for the development of genetic or pharmaceutical interventions for the treatment of mitochondrial malfunction in complex disease are also explored.

There is accumulating evidence that mitochondrial respiratory malfunction is associated with aging-associated complex diseases. However, progress in our understanding of these diseases has been hampered by the sensitivity and throughput of systems employed to quantify dysfunction and inherent limitations of the biological systems studied. In this review, we describe and contrast two methodologies that have been developed for measuring mitochondrial function to address the need for improved sensitivity and increased throughput. We then consider the utility of each methodology in studying three biological systems: isolated mitochondria, cultured cells, and cell fibers and tissues. Finally, we discuss the application of each methodology in the study of mitochondrial dysfunction in Alzheimer's disease, type 2 diabetes mellitus, and aging-associated autophagy impairment and mitochondrial malfunction. We conclude that the methodologies are complementary, and researchers may need to examine multiple biological systems to unravel complex diseases of aging.

There is a strong association between aging, diet, and immunity. The effects of macronutrients and energy intake on splanchnic and hepatic lymphocytes were studied in 15 month old mice. The mice were ad-libitum fed 1 of 25 diets varying in the ratios and amounts of protein, carbohydrate, and fat over their lifetime. Lymphocytes in liver, spleen, Peyers patches, mesenteric lymph nodes, and inguinal lymph nodes were evaluated using flow cytometry. Low protein intake reversed aging changes in splenic CD4 and CD8 T cells, CD4:CD8 T cell ratio, memory/effector CD4 T cells and naïve CD4 T cells. A similar influence of total caloric intake in these ad-libitum fed mice was not apparent. Protein intake also influenced hepatic NK cells and B cells, while protein to carbohydrate ratio influenced hepatic NKT cells. Hepatosteatosis was associated with increased energy and fat intake and changes in hepatic Tregs, effector/memory T, and NK cells. Hepatic NK cells were also associated with body fat, glucose tolerance, and leptin levels while hepatic Tregs were associated with hydrogen peroxide production by hepatic mitochondria. Dietary macronutrients, particularly protein, influence splanchnic lymphocytes in old age, with downstream associations with mitochondrial function, liver pathology, and obesity-related phenotype. [ABSTRACT FROM AUTHOR]