In vivo imaging of cell-cell interactions in the healthy and diseased brain:
Recent discoveries that we continue to explore
1. Discoveries related to the dynamics of Alzheimer’s pathology and a novel neuroprotective barrier mechanism of microglia in Alzheimer’s disease:
We discovered a previously unknown neuroprotective function of microglia in Alzheimer's disease. Microglia act as a barrier that modulates the degree of amyloid plaque compaction and accumulation of neurotoxic protofibrillar amyloid hotspots around plaques. Microglia envelopment of plaques insulates surrounding neurites from neurotoxic amyloid reducing formation of dystrophic neurites. The importance of this cellular mechanism was recently highlighted by the finding of TREM2 loss of function mutations in humans which lead to reduced microglia coverage of plaques and worse cognitive outcome. In addition, we have been at the forefront of developing methods for cellular imaging of the progression of amyloid pathology in vivo (see below in vivo two photon amyloid imaging and a novel fixed tissue time-stamp method for extracting dynamic information of plaque accumulation in postmortem tissue by serial labeling with multicolor amyloid binding dyes followed by high-throughput histological analysis.
- TREM2 Haplodeficiency in Mice and Humans Impairs the Microglia Barrier Function Leading to Decreased Amyloid Compaction and Severe Axonal Dystrophy.Yuan P, Condello C, Keene CD, Wang Y, Bird TD, Paul SM, Luo W, Colonna M, Baddeley D, Grutzendler J. Neuron. 2016 May 18. PMID: 27196974.
- Attenuation of β-Amyloid Deposition and Neurotoxicity by Chemogenetic Modulation of Neural Activity.Yuan P, Grutzendler J. J Neurosci. 2016 Jan 13. PMID: 26758850.
- Microglia constitute a barrier that prevents neurotoxic protofibrillar Aβ42 hotspots around plaques.Condello C, Yuan P, Schain A, Grutzendler J. Nat Commun. 2015 Jan 29; 2015 Jan 29. PMID: 25630253.
2. Discovery of an innate mechanism of microvascular recanalization alternative to the fibrinolytic system:
The fibrinolytic system has been recognized as the principal mechanism in charge of clearing the vasculature from occluding thromboemboli. Our data challenges the existing paradigm by describing an additional innate mechanism of microvascular recanalization capable of clearing emboli composed of a variety of substances including those not susceptible to fibrinolysis. This novel mechanism which we termed ”Angiophagy”, involves rapid remodeling of the endothelium, engulfment of the occluding embolus and its translocation through the arteriolar vascular wall. This discovery promises to greatly impact our understanding and treatment of thromboembolic disorders and the ischemia no-reflow phenomenon.
- Angiophagy prevents early embolus washout but recanalizes microvessels through embolus extravasation.Grutzendler J, Murikinati S, Hiner B, Ji L, Lam CK, Yoo T, Gupta S, Hafler BP, Adelman RA, Yuan P, Rodriguez G. Sci Transl Med. 2014 Mar 5. PMID: 24598589.
- Embolus extravasation is an alternative mechanism for cerebral microvascular recanalization.Lam CK, Yoo T, Hiner B, Liu Z, Grutzendler J. Nature. 2010 May 27. PMID: 20505729.
3. Development of a label-free technique for high-resolution imaging of myelinated axons in vivo:
Developed a label-free technique (Spectral Confocal Reflection Microscopy-SCoRe) to image myelinated axons in vivo. This technique allowed for the first time high-resolution in vivo imaging of brain myelin development and pathology in mice and is being explored for potential in vivo diagnostic applications in peripheral nerve human disorders. This method is now complemented by our discovery that a dye called sulforhodamine 101 can label oligodendrocytes in vivo and reveal gap junction transfer between astrocytes and oligodendrocytes. Together these methods open an entirely new capability to study myelin development and pathology and functional interactions with astrocytes in living mice and other animals.
- In vivo imaging of oligodendrocytes with sulforhodamine 101.Hill RA, Grutzendler J. Nat Methods. 2014 Nov. PMID: 25357236.
- Label-free in vivo imaging of myelinated axons in health and disease with spectral confocal reflectance microscopy.Schain AJ, Hill RA, Grutzendler J. Nat Med. 2014 Apr; 2014 Mar 30. PMID: 24681598.
4. Discoveries related to microvascular plasticity and regulation of cerebral blood flow:
First longitudinal in vivo imaging study of the postnatal cerebral microvasculature demonstrating that the final microvascular patterning occurs by a strategy of refinement involving sprouting and pruning. Discovered the existence of a critical period for postnatal cerebral microvascular remodeling during which disruption of neural activity leads to permanent reductions in microvascular density. This finding has important implications potentially linking perinatal homeostatic disruptions with adult life reduction in microvascular reserve which could have implications in brain susceptibility to insults and age related cognitive decline. Characterization of microvascular mural cell involvement in neurovascular coupling demonstrating that contrary to previous literature, pericytes do not play a direct contractile role but likely play cell-to-cell signaling roles that could be involved in neurovascular coupling.
- Regional Blood Flow in the Normal and Ischemic Brain Is Controlled by Arteriolar Smooth Muscle Cell Contractility and Not by Capillary Pericytes.Hill RA, Tong L, Yuan P, Murikinati S, Gupta S, Grutzendler J. Neuron. 2015 Jul 1; 2015 Jun 25. PMID: 26119027.
- Perturbed neural activity disrupts cerebral angiogenesis during a postnatal critical period.Whiteus C, Freitas C, Grutzendler J. Nature. 2014 Jan 16; 2013 Dec 4. PMID: 24305053.
- In vivo imaging of cerebral microvascular plasticity from birth to death.Harb R, Whiteus C, Freitas C, Grutzendler J. J Cereb Blood Flow Metab. 2013 Jan; 2012 Oct 24. PMID: 23093067.