Microtubule-associated protein tau in murine kidney: role in podocyte architecture

Abstract

Tau is a cytoskeletal protein that is expressed mainly in neurons and is involved in several cellular processes, such as microtubule stabilization, axonal maintenance, and transport. Altered tau metabolism is related to different tauopathies being the most important Alzheimer’s disease where aberrant hyperphosphorylated and aggregated tau is found in the central nervous system. Here, we have analyzed that function in kidney by using tau knockout mice generated by integrating GFP-encoding cDNA into exon 1 of MAPT (here referred to as TauGFP/GFP). IVIS Lumina from PerkinElmer demonstrated GFP expression in the kidney. We then demonstrated by qPCR that the main tau isoform in the kidney is Tau4R. The GFP reporter allowed us to demonstrate that tau is found in the glomeruli of the renal cortex, and specifically in podocytes. This was further confirmed by immunohistochemistry. TauGFP/GFP mice present a podocyte cytoskeleton more dynamic as they contain higher levels of detyrosinated tubulin than wild-type mice. In addition, transmission electron microscopy studies demonstrated glomerular damage with a decrease in urinary creatinine. Our results prove that tau has an important role in kidney metabolism under normal physiological conditions.

Mouse and Human Tau Expression in Different Brain Areas

“…Mouse brain tissue preserved at –80°C was homogenized to obtain the extracts in RIPA buffer as described before [ 9 ]. Next, the protein concentration of each homogenate was determined by the Bradford method [ 12 ], using the BCA test (Thermo Fisher).…”

“…Next, the protein concentration of each homogenate was determined by the Bradford method [ 12 ], using the BCA test (Thermo Fisher). Finally, the SDS-PAGE buffer used in [ 9 ] was added to the protein extracts obtained. The extracts were boiled in a thermoblock at 100°C for 5 min.…”

“…These mice allowed us to study Mapt gene expression precisely as a function of age, brain region, and cellular component. Furthermore, these mice allowed us to study the expression of tau without post-translational modifications in murine brain, because we have analyzed it by quantifying expression of green fluorescent protein (GFP) under the endogenous tau promoter [ 9 ]. We have measured GFP levels in three brain areas: cortex, hippocampus, and cerebellum.…”

Identification and characterization of a MAPT-targeting locked nucleic acid antisense oligonucleotide therapeutic for tauopathies

“…Upon systemic dosing, class-related adverse effects have been reported due to accumulation of ASO in the kidney tubule. 45 Due to tau expression in glomeruli and regulation of kidney metabolism, 51 further evaluation of accumulation of ASO-001933 in kidney may be warranted; however, the risk of peripheral side effects is expected to be low when ASO is delivered directly and infrequently into the CNS. Accumulation at the site of administration in the spinal cord may also require further evaluation in nonclinical species.…”

“…Characterization of Tau KO mice has revealed metabolic, cognitive, and motor dysfunction in mice homozygous for the MAPT gene deletion, depending on the age and strain of the mice. 46 , 47 , 48 , 49 , 50 , 51 , 52 Few, if any, studies report adverse phenotypes in mice heterozygous for the MAPT deletion, indicating that 50% loss of wild-type transcript is anticipated to be safe in humans. One caveat to interpreting such studies is the use of a constitutive deletion of MAPT from birth, which differs from the intended therapeutic approach.…”