Eosinophilic neuronal inclusions in the thalamus of ageing B6C3F1 mice

Inorganic phosphate exporter heterozygosity in mice leads to brain vascular calcification, microangiopathy, and microgliosis

Calcification of the cerebral microvessels in the basal ganglia in the absence of systemic calcium and phosphate imbalance is a hallmark of primary familial brain calcification (PFBC), a rare neurodegenerative disorder. Mutation in genes encoding for sodium-dependent phosphate transporter 2 (SLC20A2), xenotropic and polytropic retrovirus receptor 1 (XPR1), platelet-derived growth factor B (PDGFB), platelet-derived growth factor receptor beta (PDGFRB), myogenesis regulating glycosidase (MYORG), and junctional adhesion molecule 2 (JAM2) are known to cause PFBC. Loss-of-function mutations in XPR1, the only known inorganic phosphate exporter in metazoans, causing dominantly inherited PFBC was first reported in 2015 but until now no studies in the brain have addressed whether loss of one functional allele leads to pathological alterations in mice, a commonly used organism to model human diseases. Here we show that mice heterozygous for Xpr1 (Xpr1WT/lacZ ) present with reduced inorganic phosphate levels in the cerebrospinal fluid and age- and sex-dependent growth of vascular calcifications in the thalamus. Vascular calcifications are surrounded by vascular basement membrane and are located at arterioles in the smooth muscle layer. Similar to previously characterized PFBC mouse models, vascular calcifications in Xpr1WT/lacZ mice contain bone matrix proteins and are surrounded by reactive astrocytes and microglia. However, microglial activation is not confined to calcified vessels but shows a widespread presence. In addition to vascular calcifications, we observed vessel tortuosity and transmission electron microscopy analysis revealed microangiopathy-endothelial swelling, phenotypic alterations in vascular smooth muscle cells, and thickening of the basement membrane.

Ageing-associated phenotypes in mice

Ageing is a continuous process in life featuring progressive damage accumulation that leads to physiological decline, functional deterioration and ultimately death of an organism. Based on the relatively close anatomical and physiological similarity to humans, the mouse has been proven as a valuable model organism in ageing research over the last decades. In this review, we survey methods and tools currently in use to assess ageing phenotypes in mice. We summarize a range of ageing-associated alterations detectable at two major levels of analysis: (1) physiology and pathophysiology and (2) molecular biomarkers. Age-sensitive phenotypes provided in this article may serve to inform future studies targeting various aspects of organismal ageing in mice. In addition, we discuss conceptual and technical challenges faced by previous ageing studies in mice and, where possible, provide recommendations on how to resolve some of these issues.

Brain and spinal cord lesions in 28 inbred strains of aging mice

Brain and spinal cord histopathology findings in male and female 20-month-old mice in a large-scale aging study of 28 inbred Jackson Laboratory mouse strains from 7 genetic families are described. Brain sections from selected strains at 12 and 24 months of age or older were also reviewed. Common lesions include axonal dystrophy in the gracile and/or cuneate nucleus in the sensory tract of the dorsal medulla and in the spinal cord in all strains. Hirano-like bodies were seen in 24/28 strains, and mineralization was observed in the thalamus of 9/28 strains. Less common lesions were also seen in the cerebellum, cerebral cortex, and other brain areas. No brain or spinal cord tumors were found. Evidence of an impairment of the ubiquitin-proteasome system (UPS) and/or suspected autophagy was manifested as medullary axonal dystrophy with intra-axonal granular eosinophilic bodies and LC3B immunohistochemistry in most strains. RIIIS/J, the most severely affected strain, showed moderate axonal dystrophy at 12 months, which progressed to severe lesions at 20 months. Comparative pathology in various species is discussed.

Neuronal inclusions resembling Negri bodies in the thalamus of a red kangaroo (Macropus rufus)

Eosinophilic intracytoplasmic neuronal inclusions resembling Negri bodies, but not associated with lyssaviral infection, were detected in the ventrolateral thalamus of a young-adult, male red kangaroo (Macropus rufus). Similar neuronal inclusions, also with a regional distribution in the brain, have been reported as an incidental, possibly age-related finding in other animal species.

Spontaneous Incidental Brain Lesions in C57BL/6J Mice

Genetically engineered mouse lines on a C57BL/6J background are widely employed as preclinical models to study neurodegenerative human disorders and brain tumors. However, because of the lack of comprehensive data on the spontaneous background neuropathology of the C57BL/6J strain, discriminating between naturally occurring changes and lesions caused by experimental mutations can be challenging. In this context, this study aims at defining the spectrum and frequency of spontaneous brain changes in a large cohort of C57BL/6J mice and their association with specific biological variables, including age and sex. Brains from 203 experimentally naive and clinically unremarkable C57BL/6J mice were collected and analyzed by means of histopathology and immunohistochemistry. Mice ranged in age from 3 to 110 weeks with 89 females, 111 males, and 3 unknowns. Sixteen different spontaneous lesion categories were described in this cohort. Age-related neurodegenerative and/or neuroinflammatory findings represented the most common pathologic changes and included (1) Hirano-like inclusions in the thalamic neurons, (2) neuroaxonal dystrophy in the medulla oblongata, (3) periodic acid-Schiff-positive granular deposits in the neuropil of the hippocampus, and (4) progressive neuroinflammation characterized by microgliosis and astrogliosis. Neoplastic conditions, developmental abnormalities, and circulatory disorders were rarely observed incidental findings. In conclusion, this study describes spontaneous age-related brain lesions of the C57BL/6J mouse and provides a reference for evaluating and interpreting the neuropathological phenotype in genetically engineered mouse models developed and maintained on this congenic background.

Every-other-day feeding extends lifespan but fails to delay many symptoms of aging in mice

Dietary restriction regimes extend lifespan in various animal models. Here we show that longevity in male C57BL/6J mice subjected to every-other-day feeding is associated with a delayed onset of neoplastic disease that naturally limits lifespan in these animals. We compare more than 200 phenotypes in over 20 tissues in aged animals fed with a lifelong every-other-day feeding or ad libitum access to food diet to determine whether molecular, cellular, physiological and histopathological aging features develop more slowly in every-other-day feeding mice than in controls. We also analyze the effects of every-other-day feeding on young mice on shorter-term every-other-day feeding or ad libitum to account for possible aging-independent restriction effects. Our large-scale analysis reveals overall only limited evidence for a retardation of the aging rate in every-other-day feeding mice. The data indicate that every-other-day feeding-induced longevity is sufficiently explained by delays in life-limiting neoplastic disorders and is not associated with a more general slowing of the aging process in mice.

Dietary restriction can extend the life of various model organisms. Here, Xie et al. show that intermittent periods of fasting achieved through every-other-day feeding protect mice against neoplastic disease but do not broadly delay organismal aging in animals.

Thalamic calcification in vitamin D receptor knockout mice

Vitamin D is a steroid hormone with many important functions in the brain, mediated through the nuclear vitamin D receptor. Here, we report that aging nuclear vitamin D receptor knockout mice demonstrate a symmetric thalamic calcification with numerous Ca/P-containing laminated bodies. These results are consistent with clinical findings showing brain calcification in patients with vitamin D deficiency. Our results suggest that nuclear vitamin D receptor deficiency leads to brain mineralization in vitamin D receptor knockout mice, which may represent an experimental model of intracranial calcification.

Accumulation of Ym1/2 protein in the mouse olfactory epithelium during regeneration and aging

A unique feature of the olfactory system is its efficiency to produce new neurons in the adult. Thus, destruction of the olfactory receptor neurons (ORNs) using chemical (intranasal perfusion with ZnSO4) or surgical (axotomy or bulbectomy) methods, leads to an enhanced rate of proliferation of their progenitors and to complete ORNs regeneration. The aim of our study was to identify new factors implied in this regenerative process. Using an electrophoretic method, we observed the accumulation of a 42 kDa protein after axotomy in the olfactory mucosa, but not in the olfactory bulb. Its expression started after a few days following injury and increased massively during the phase of ORN regeneration. The purification and the sequence characterization revealed that this protein was Ym1/2, recently identified in activated macrophages present in various tissues during inflammation. Western blotting analysis of Ym1/2 confirmed the accumulation of this protein in the regenerating olfactory mucosa consecutively to olfactory axotomy or bulbectomy but also after ZnSO4 irrigation of the nasal cavity. In the olfactory mucosa of control mice, Ym1/2 was hardly detectable in young animals and became more and more abundant with increasing age. In injured and aged mice, Ym1/2 mainly accumulates in the cytoplasm of supporting cells as well as in other cells located throughout the olfactory epithelium. Our results suggest that Ym1/2 is involved in olfactory epithelium remodeling following several kinds of lesions of the adult olfactory mucosa and support the view of a critical role of inflammatory cues in neurodegeneration and aging.

Structural brain aging in inbred mice: potential for genetic linkage

To identify genetic factors involved in brain aging, we have initiated studies assessing behavioral and structural changes with aging among inbred mouse strains. Cognitive performance of C57BL/6J mice is largely maintained with aging, and stereological analysis revealed no significant age-related change in neuron number, synaptic bouton number or glial number in the hippocampus. Moreover, no change in cortical neuron number and cholinergic basal forebrain neuron number has been found in this strain. 129Sv/J mice have more pronounced age-related cognitive deficits, although hippocampal and basal cholinergic forebrain neuron number also appear unchanged with aging. Differences in neurogenesis and neuron vulnerability in the adult CNS of C57BL/6, 129/Sv and other inbred strains have been reported, which in turn may have important consequences for brain aging. Age-related lesions, such as thalamic eosinophilic inclusions and hippocampal clusters of polyglucosan bodies also vary greatly among inbred strains although the functional significance of these lesions is not clear. The continued assessment of such age-related structural and behavioral changes among inbred mouse strains offers the potential to identify genes that control age-related changes in brain structure and function.