Changes in murine tissue concentrations of dolichol and dolichol derivatives associated with age

Glycoconjugate journal special issue on: the glycobiology of Parkinson's disease

Parkinson's disease (PD) is a neurodegenerative disorder that affects over 10 million aging people worldwide. This condition is characterized by the degeneration of dopaminergic neurons in the pars compacta region of the substantia nigra (SNpc) and by aggregation of proteins, commonly α-synuclein (SNCA). The formation of Lewy bodies that encapsulate aggregated proteins in lipid vesicles is a hallmark of PD. Glycosylation of proteins and neuroinflammation are involved in the pathogenesis. SNCA has many posttranslational modifications and interacts with components of membranes that affect aggregation. The large membrane lipid dolichol accumulates in the brain upon age and has a significant effect on membrane structure. The replacement of dopamine and dopaminergic neurons are at the forefront of therapeutic development. This review examines the role of membrane lipids, glycolipids, glycoproteins and dopamine in the aggregation of SNCA and development of PD. We discuss the SNCA-dopamine-neuromelanin-dolichol axis and the role of membranes in neuronal stem cells that could be a regenerative therapy for PD patients.

Identification of functional lipid metabolism biomarkers of brown adipose tissue aging

OBJECTIVE

Aging is accompanied by loss of brown adipocytes and a decline in their thermogenic potential, which may exacerbate the development of adiposity and other metabolic disorders. Presently, only limited evidence exists describing the molecular alterations leading to impaired brown adipogenesis with aging and the contribution of these processes to changes of systemic energy metabolism.

METHODS

Samples of young and aged murine brown and white adipose tissue were used to compare age-related changes of brown adipogenic gene expression and thermogenesis-related lipid mobilization. To identify potential markers of brown adipose tissue aging, non-targeted proteomic and metabolomic as well as targeted lipid analyses were conducted on young and aged tissue samples. Subsequently, the effects of several candidate lipid classes on brown adipocyte function were examined.

RESULTS

Corroborating previous reports of reduced expression of uncoupling protein-1, we observe impaired signaling required for lipid mobilization in aged brown fat after adrenergic stimulation. Omics analyses additionally confirm the age-related impairment of lipid homeostasis and reveal the accumulation of specific lipid classes, including certain sphingolipids, ceramides, and dolichols in aged brown fat. While ceramides as well as enzymes of dolichol metabolism inhibit brown adipogenesis, inhibition of sphingosine 1-phosphate receptor 2 induces brown adipocyte differentiation.

CONCLUSIONS

Our functional analyses show that changes in specific lipid species, as observed during aging, may contribute to reduced thermogenic potential. They thus uncover potential biomarkers of aging as well as molecular mechanisms that could contribute to the degradation of brown adipocytes, thereby providing potential treatment strategies of age-related metabolic conditions.

A Convenient Method for the Synthesis of (S)-Dolichol and (S)-Nordolichol

A procedure for the preparation of (S)-dolichol and (S)-nor-dolichol starting from the polyprenyl fraction extracted from Gingko Biloba integer or extracted leaves is described. Two chiral isoprenoid compounds in good yields and high degree of enantiomeric excess were obtained. The (S)-nordolichol appears to be a good chiral precursor for the preparation of 14C-labeled (S)-dolichol which is to be used in investigations aimed at gaining further information with respect to the role of dolichol in the function of living cells.

Dolichol: A Component of the Cellular Antioxidant Machinery

Dolichol, an end product of the mevalonate pathway, has been proposed as a biomarker of aging, but its biological role, not to mention its catabolism, has not been fully understood. UV-B radiation was used to induce oxidative stress in isolated rat hepatocytes by the collagenase method. Effects on dolichol, phospholipid-bound polyunsaturated fatty acids (PL-PUFA) and known lipid soluble antioxidants [coenzyme Q (CoQ) and α-tocopherol] were studied. The increase in oxidative stress was detected by a probe sensitive to reactive oxygen species (ROS). Peroxidation of lipids was assessed by measuring the release of thiobarbituric acid reactive substances (TBARS). Dolichol, CoQ, and α-tocopherol were assessed by high-pressure liquid chromatography (HPLC), PL-PUFA by gas-liquid chromatography (GC). UV-B radiation caused an immediate increase in ROS as well as lipid peroxidation and a simultaneous decrease in the levels of dolichol and lipid soluble antioxidants. Decrease in dolichol paralleled changes in CoQ levels and was smaller to that in α-tocopherol. The addition of mevinolin, a competitive inhibitor of the enzyme 3-hydroxy-3-methylglutaryl CoA reductase (HMG-CoAR), magnified the loss of dolichol and was associated with an increase in TBARS production. Changes in PL-PUFA were minor. These findings highlight that oxidative stress has very early and similar effects on dolichol and lipid soluble antioxidants. Lower levels of dolichol are associated with enhanced peroxidation of lipids, which suggest that dolichol may have a protective role in the antioxidant machinery of cell membranes and perhaps be a key to understanding some adverse effects of statin therapy.

Accumulation of Dolichol in Older Tissues Satisfies the Proposed Criteria To Be Qualified a Biomarker of Aging

Criteria for defining biomarkers have been suggested. Accumulation of dolichol in tissues of older animals meets the following criteria: (a) levels of dolichol exhibit a quantitative correlation with age in all tissues and are not altered by several age-dependent diseases in the same direction as that of aging; (b) accumulation is not secondary to metabolic changes of aging and is altered appropriately by factors that modulate the aging rate like caloric restriction and physical exercise; (c) biomarker is applicable to different tissues across mammalian species, including humans, and to trisomy 21 and its hypothalamic digoxin-mediated model. Reliable changes in tissue dolichol levels are seen in relatively short intervals of time compared to over a life span, and levels can be tested on a small amount of tissue without causing death of the animal. In this article, we show applications to the study of host-graft interaction and detection of gender-related differences in biological age, and we discuss mechanism(s) of accumulation.

Dolichol levels in younger and older rat hearts heterotopically transplanted in younger recipients

Dolichol (D) levels increase dramatically in older tissue. An understanding of the exchangeability of D between tissues may be essential in order to understand the mechanism of the abnormal accumulation associated with aging. The question was investigated by the use of organ transplantation. D-poor hearts donated by 3-mon-old and D-rich by 22-mon-old male Lewis rats were transplanted heterotopically in 3-mon-old syngenic recipients, whose peripheral tissues and liver were poor in D. Native and transplanted hearts were taken 7 and 21 d after surgery. Native hearts of 3-mon- and 22-mon-old male Lewis rats served as control. D concentration and quantity were higher in older than in younger native hearts as expected. In the transplanted hearts, the quantity of D was unchanged, irrespective of the age of the donor and of the time of transplantation, whereas D concentration increased because of the remarkable disuse atrophy. No changes in D were observed in recipients' tissues. It is concluded that dolichol is not redistributed via circulation from the transplanted heart to the tissues and liver of the younger recipient.

Effects of ageing and increased haemolysis on the levels of dolichol in rat spleen

Dolichol is a long-chain polyisoprenoid. No enzyme pathway for dolichol degradation was discovered. Dolichol accumulates in human and rodent tissues during ageing. Red blood cells contain a larger amount of dolichol and red blood cell life span is shorter in older rats. The effects of age and of the load of dolichol from red blood cell degradation on the ageing-associated accumulation of dolichol in spleen were studied in 2, 6, 12, 18 and 24 month-old male Sprague Dawley rats fed ad libitum (AL) or on an anti-ageing dietary regimen (EOD). Tissue dolichol was extracted and assayed by HPLC [J. Gerontol. 53A (1998) B87]. Levels of dolichol increased in spleen, liver, kidney and muscle in parallel fashion from the age of 2 to 12 months. Unexpectedly, spleen dolichol decreased in older rats whereas liver, kidney and muscle dolichol increased significantly. The effects of haemolysis on spleen dolichol were tested by the administration of phenylhydrazine. Results show that haemolysis does not increase, but rather decreases the levels of dolichol in erythroclastic organs. It is concluded that the levels of spleen dolichol may decrease in the absence of any known enzymatic degradative pathway if the spleen and its resident phagocytes are forced to cope with a higher number of red blood cells to be cleared. Free-radical mediated decomposition of dolichol by phagocytic cells during erythrophagocytosis might be involved in the process.

Novel dolichyl derivatives in rat spleen

Novel dolichyl derivatives were found in rat spleen. The compounds were eluted from reverse phase HPLC after eluting dolichyl fatty acid ester. The elution profiles of the unsaponified forms of the unknown compounds were coincident with that of dolichol from spleen on reverse phase HPLC. The compounds were not dolichyl dolichoate, which are present in bovine thyroid. The compounds were not found in young rats (4 months of age) but were found in old rats (above 12 months of age), and they were not detected in other tissues under our conditions.

Dolichol-mediated enhanced protein N-glycosylation in experimental diabetes--a possible additional deleterious effect of hyperglycemia

In liver cells from diabetic rats, an increased incorporation of labeled glucosamine into cellular and secretory proteins was found, when related to the incorporation of labeled leucine. This increased N-glycosylation was present in the face of decreased synthesis of hepatic cellular and secretory proteins evident from reduced leucine incorporation and diminished glycosyltransferase activity. To elucidate the mechanisms involved we incubated isolated hepatocytes with two N-glycosylation inhibitors: tunicamycin and 2-deoxyglucose. Tunicamycin exerted a marked inhibitory effect on the incorporation rate of labeled glucosamine into proteins in liver cells from diabetic rats, while 2-deoxyglucose had a negligible effect on this process in these cells. These diverse effects might be explained by the fact that tunicamycin acts through strong association with the enzyme catalyzing the first step in glycoprotein synthesis, namely, the transfer of UDP-GlcNAc to dolichol-P (indicating noncompetitive inhibition). This enzyme is reduced in liver cells from diabetic animals. On the other hand, 2-deoxyglucose exerts its effect by being attached to dolichol-P, preventing further elongation of oligosaccharide chain on the protein backbone. This latter effect might be eliminated by excess dolichol-P (indicating competitive inhibition). The dolichol content in liver extract from diabetic rats was about 2.5-fold higher compared with nondiabetic rats (51.6 micrograms/g versus 20.6 micrograms/g wet liver weight). These two lines of evidence confirm the notion that the enhanced enzymatic glycosylation in liver from diabetic animals is maintained by an increased hepatic dolichol concentration, which is most probably related to the hyperglycemia. Thus, the dolichol-N-glycosylation pathway may represent another detrimental aspect of hyperglycemia and may operate by dolichol mass action rather than through glycosylating enzyme activity.

Effects of aging and diet on the accumulation of dolichol in rat tissues

A diet containing 15% (w/w) fat and 20% (w/w) of either casein or soy protein was fed to rats between 1 and 18 months of age. The effects of these dietary proteins on the accumulation of cholesterol and dolichols in kidney, spleen, brain, and heart were studied. The amount of cholesterol in these tissues was not influenced by the diet. In kidney and spleen, the amount of dolichols in rats fed the experimental diets was 50-70% higher than those in rats fed the lab chow diet. The contents of spleen dolichols in rats fed the soy protein diet tended to be higher than those in rats fed the casein diet. The amount of dolichols in heart and brain was not influenced by the diet. The proportion of spleen dolichyl fatty ester in rats fed the experimental diets was higher than that in rats fed the lab chow. The distribution of the dolichol isoprenologues was not influenced by the diet. There was a shift in the dolichol isoprenologues in kidney and spleen toward ones of lower chain length until 2 months of age, and after that there was no change. However, in heart and brain they shifted toward ones of lower chain length with aging. Our results suggested that dolichol metabolism may be influenced by fat content in the diets and differed among rat tissues.