Critical Role Of Neuronal Vps35 In Blood Vessel Branching And Maturation In Developing Mouse Brain

Neurodegenerative diseases are characterized by progressive dysfunction of neurons and loss of neurons in the central nervous system(CNS).It is the major cause of cognitive and motor dysfunction.Recent research also show that neurodegenerative diseases are accompanied by dysfunction of blood vessels(BV).Thus,it would be valuable to explore the impact of vascular system on the pathology of neurodegenerative diseases.Multiple risk factors contribute to the development of neurodegeneration,including genetic mutations,aging,and environmental factors.Among these risk factors,genetic mutations are believed to be the primary causal factor.Vacuolar protein sorting 35(Vps35),a key component of retromer,plays a crucial role in selective retrieval of transmembrane proteins from endosomes to Trans-Golgi networks.Mutations in Vps35 have been reported in patients with Alzheimer’s disease(AD)and Parkinson’s disease(PD),suggesting that Vps35 dysfunction may be a causal risk factor for neurodegenerative disorders.Vps35 is highly expressed in developing pyramidal neurons of mouse neocortex and hippocampus,which is a critical period for neuronal development and angiogenesis.However,it remains largely unclear the exact physiological function of Vps35 in the developing neurons,and whether knock out of Vps35 affect the development and function of blood vessels remains to be studied.Here,we provide evidence that selectively knocking out Vps35 gene in embryonic cortical pyramidal neurons results in several developmental defects,including cortical atrophy,neuronal terminal differentiation deficits,neuron degeneration and apoptosis.These neuronal deficits are also accompanied with reactivation of glial cells and accumulation of autophagosome protein P62/sequestosome 1(SQSTM1)and neurodegeneration associated protein TAR DNA-Binding Protein 43(Tdp43).These changes resemble the pathological features of frontotemporal dementia(FTD).In addition,we also provide evidence that the function of embryonic neuronal Vps35 is critical for blood vessel branching and maturation.Vps35-KO in mouse embryonic pyramidal neurons result in reductions of blood vessel branching and density,arteriole diameter,and BV-associated pericytes and microglia,but an increase in BV-associated reactive astrocytes.However,selectively deletion of Vps35 gene in postnatal pyramidal neurons didn’t display such phenotypes.These results suggest that the critical period of Vps35 mediated angiogenesis is at early developmental stage.We next used pexidartinib(PLX3397),which could block microglial proliferation and survival,to treat the mice and found that the blood vessel deficits in mutant mice were strengthened.And the BVassociated astrocytes reactivation exhibited more drastic enhancement,suggesting the vascular defects may be related to the reactivation of microglia and astrocytes.Finally,we find that knocking down Vps35 results in decreased secretion of certain extracellular matrix(ECM)proteins,resulting in defects of integrin signaling pathway.These results implicated that the changes of ECM components of neurons may further trigger the glial activation and deficit in blood vessel branching and maturation.Taken together,Vps35-KO in mouse embryonic pyramidal neurons resulted in neurodegenerative disease phenotypes,which was accompanied by changes in ECM components,reductions of blood vessel branching and density,and increase of BV-associated astrocytes reactivation.Our results demonstrate neuronal Vps35 functions in neurovascular unit(NVU)in developing mouse brain,suggesting that Vps35 may contribute to the pathogenesis of neurodegenerative disorders by regulating BV branching and maturation.