Microautophagy,+Macroautophagy,+and+Organelle-Specific+Autophagy


 * Autophagy:** The process of self-digestion by a cell through the action of enzymes originating within the same cell.


 * Why? **
 * Dysfunctional part of the cell
 * Lack of nutrients in cell



==== Figure 1: Overview of Microautophagy, macroautophagy, organelle-specific autophagy and chaperone-mediated autophagy. From source: "Macroautophagy, microautophagy and chaperone-mediated autophagy are the principal lysosomal degradation pathways in mammalian cells. Black arrows show evolution of structures, while gray double-ended arrows indicate fusion. Lysosomes differ from late endosomes by the absence of mannose phosphate receptors. Autophagosomes form autophagolysosomes by fusion either with late endosomes or lysosomes." ==== (http://cardiovascres.oxfordjournals.org/content/68/3/355/F1.expansion)


 * Microautophagy **
 * particles to be degraded are taken in by the lysosome directly
 * the lysosome degrades the particles and secretes them outside of the cell
 * Nonspecific


 * Macroautophagy **
 * particles to be degraded are surrounded by an elongating membrane
 * when membrane fully encases particles, is known as an autophagosome
 * can fuse with either a late endosome or a lysosome and be degraded and secreted from cell
 * Nonspecific


 * Organelle-specific Autophagy **
 * Can be either micro or macroautophagy in terms of how the particles are degraded
 * Targets specific organelles that are either not functioning correctly or at all

The process of autophagy is extremely important to cell biology due to its role in removing dysfunctional and/or non functioning particles. Autophagy prevents cells from becoming too large, as well as helping cells in a nutrient crisis: when the cell cannot get nutrients from outside sources, it can use autophagy for a short time to fuel its energy requirements.

Alzheimer’s disease: a progressive, degenerative disorder that attacks the brain's nerve cells, or neurons, resulting in loss of memory, thinking and language skills, and behavioral changes. – www.alzfdn.org

Alois Alzheimer, in his report of the first case of Alzheimer disease (AD) in 1907, described the two pathologic lesions that have remained the diagnostic hallmarks of the disease: the neurofibrillary tangle and the senile plaque.

Funderburk et. al. (2010) studied the link between autophagy and Alzheimer’s disease, Parkinson’s disease, and Huntington’s disease. The exact mechanism in the paper was still considered unclear as to how autophagy has a role in each neuropathological condition. However, it is suggested that aggregates in cells that are not taken care of by autophagy could play a part, meaning that a dysfunctional autophagy response was partly to blame. Barnett & Brewer (2011) discuss the idea that aging and alzheimer’s disease could be linked to either overactive or underactive autophagy. Nixon (2007) gave an overview of how Alzheimer’s disease works, how autophagy works, and how they could be connected. The conclusion of the paper states there is evidence neuronal autophagy is induced in Alzheimer’s disease, but is also impaired at late steps in the pathway, resulting in aggregates, which could also lead to plaque formation.

**References:** Barnett, A. & Brewer, G.J. (2011). Autophagy in aging and Alzheimer’s disease: pathologic or protective? //Journal of Alzheimer’s Disease//, **25 (3)**: 385-394. Funderburk, S.F., Marcellino, B.K., & Yue, Z. (2010). Cell “Self-Eating” (Autophagy) Mechanism in Alzheimer’s Disease. //Mount Sinai Journal of Medicine//, **77 (1)**: 59-68. Li WW, Li J, Bao JK. (2012). Microautophagy: lesser-known self-eating. Cell Mol Life Sci. ** 69(7) ** :1125-36. Nixon, R. (2007). Autophagy, amyloidogenesis and Alzheimer disease. //Journal of Cell Science,// **120**, 4081-4091