Reversal of a hallmark of brain ageing: lipofuscin accumulation.

The prospect of removing cellular deposits of lipofuscin is of considerable interest because they may contribute to age related functional decline and disease. Here, we use a decapod crustacean model to circumvent a number of problems inherent in previous studies on lipofuscin loss. We employ (a) validated lipofuscin quantification methods, (b) an in vivo context, (c) essentially natural environmental conditions and (d) a situation without accelerated production of residual material or (e) application of pharmacological compounds. We use a novel CNS biopsy technique that produces both an anti-ageing effect and also permits longitudinal sampling of individuals, thus (f) avoiding conventional purely cross-sectional population data that may suffer from selective mortality biases. We quantitatively demonstrate that lipofuscin, accrued through normal ageing, can be lost from neural tissue. The mechanism of loss probably involves exocytosis and possibly blood transport. If non-disruptive ways to accelerate lipofuscin removal can be found, our results suggest that therapeutic reversal of this most universal manifestation of cellular ageing may be possible.

A flow-cytometric method for quantification of neurolipofuscin and comparison with existing histological and biochemical approaches.

The ability to measure lipofuscin accumulation accurately is essential for understanding its role in physiological ageing and human disease, and for its recent use as an ecological tool for age determination. Existing quantification methods are problematic. In situ histological measurement by microscopy can be very precise but is labour intensive. Spectrofluorimetric measurement of whole lipid extracts is rapid but not sufficiently specific. A recent HPLC assay for the retinal pigment epithelium lipofuscin fluorophore, A2-E, is potentially both precise and rapid but not applicable to lipofuscin in other tissues, or from fixed samples. In this study, I explore the use of flow cytometry or fluorescence activated cell sorting (FACS) for specific quantification of lipofuscin granules in formalin-fixed CNS homogenates from lobsters (Homarus gammarus). Free neurolipofuscin granules were discriminated in FACS samples by their size distribution (forward scatter), distinctive orange autofluorescence (FL3) and refractive internal structure (side scatter). A quantitative neurolipofuscin index was developed, which was highly correlated with the microscopically measured neurolipofuscin concentration in the same tissue. Sample-processing rate was at least an order of magnitude greater for FACS than for quantitative microscopy but the latter yielded a much more precise estimate of neurolipofuscin concentration. While the FACS approach may be ideal where rapid handling and only semiquantitative results are required, loss of precision will preclude use in many ecological studies where the highest available resolution is needed. Further refinements to the FACS approach are possible but advanced histological methods for neurolipofuscin quantification remain the most reliable at this time.

Role of environmental temperature in aging and longevity: insights from neurolipofuscin.

The available evidence for thermal modulation of neurolipofuscin deposition in poikilotherms is reviewed here and additional data are contributed. Mainly decapod crustacean models are employed and neurolipofuscin is treated as an index of physiological aging. In all cases, neurolipofuscin accumulation rate is positively correlated with environmental temperature but there appears to be lowered sensitivity in the thermal mid-range, an 'optimum' temperature for neurolipofuscin accumulation and possibly age-associated variation. The geographical position of the population within the species' thermal range may determine sensitivity of the response. There is seasonal oscillation of neurolipofuscin accumulation rate, providing preliminary evidence for neurolipofuscin turnover with net loss in winter. Spatial and temporal thermal variations of similar magnitude appear to have comparable effects on neurolipofuscin accumulation rate. Such effects may be extreme, suggesting important implications for physiological aging even in homeotherms. Inter-specific comparisons indicate that species-specific neurolipofuscin accumulation rates are positively correlated with habitat temperature and inversely correlated with maximum lifespan and age at maturity. These findings help explain some well-known bioclimatic trends in maturation- and maximum body size, such as Bergmann's rule. They also highlight the fact that global warming is likely to cause significant changes in life history parameters, population dynamics and responses to exploitation for many species.