Zehr, Cynthia

Frontotemporal lobar degeneration with ubiquitin immunoreactive inclusions (FTLD‐U) is the most common cause of frontal lobe dementia. Recently, the TAR DNA binding protein (TDP‐43) has been described as a marker for FTLD‐U. TDP‐43 has been reported to be specific for neuronal inclusions in FTLD‐U and not other degenerative disorders such as Alzheimer's disease (AD). The reported specificity of TDP‐43 makes it possible to detect FTLD‐U in the setting of other neurodegenerative diseases. On this assumption, we determined the frequency of FTLD‐U in AD. Additionally, since FTLD‐U is often associated with hippocampal sclerosis (HpScl), a process characterized by neuronal loss in Sommer's sector of the hippocampus, we also determined the frequency of FTLD‐U in HpScl. A series of 74 AD and 20 HpScl cases were screened with TDP‐43 immunohistochemistry. Immunoreactivity for TDP‐43 was detected in 13 of 20 (65%) HpScl cases and 42 of 74 (57%) AD cases, including 33 of 44 (75%) cases of AD with HpScl and 9 of 30 (30%) cases of AD without HpScl. The specificity of TDP‐43 was assessed by double immunolabeling for tau at the light and electron microscopic level. The frequency of tau and TDP‐43 co‐localization was 13%. At the EM level TDP‐43 immunoreactivity was present in cytosolic granular material, but some tau‐positive filaments were also labeled. The results suggest that FTLD‐U occurs frequently in HpScl and AD.

Progranulin is a mediator of development, tumorigenesis and wound repair. Mutations in the gene for progranulin cause frontotemporal dementia. Little is known about the role of progranulin in the nervous system. The cleavage products of progranulin, granulins, were first isolated from granule‐enriched fractions of human and equine neutrophils and from rat bone marrow. Immunohistochemistry of granulin has been reported in macrophages or monocytes. Here we use a post‐embedding immunogold labeling method to ultrastructurally localize progranulin in mouse and human tissue. Bone marrow from mouse femoral bone was fixed in 4% paraformaldehyde. Human choroid plexus and a brain abscess were obtained from autopsy brains fixed in formalin. Tissues were dehydrated in ethanols, infiltrated and embedded in LR White resin. Thin sections were collected on Formvar‐coated nickel grids and incubated with antibodies to mouse or human progranulin, followed by gold‐conjugated secondary antibodies. In all tissues progranulin was localized to secretory granules and vesicles in neutrophils and macrophages. Labeled granules had morphological features of secretory granules. They were membrane‐bound vesicles with pale to optically dense contents and ranged from 200 to 500 microns in diameter. This is the first report of the ultrastructural localization of progranulin to mouse and human neutrophils and macrophages in normal and inflammatory conditions, including neuroinflammatory disorders.

An orally bioavailable and blood–brain barrier penetrating analog of the kinase inhibitor K252a was able to prevent the typical motor deficits in the tau (P301L) transgenic mouse model (JNPL3) and markedly reduce soluble aggregated hyperphosphorylated tau. However, neurofibrillary tangle counts were not reduced in the successfully treated cohort, suggesting that the main cytotoxic effects of tau are not exerted by neurofibrillary tangles but by lower molecular mass aggregates of tau. Our findings strongly suggest that abnormal tau hyperphosphorylation plays a critical role in the development of tauopathy and suggest a previously undescribed treatment strategy for neurodegenerative diseases involving tau pathology.