What is the difference between (Aβ1-40) and (Aβ1-42)?

In mammals, the APP gene is located on chromosome 21 and has a total of 8 subtypes, whose subtypes generally contain 365~770 amino acid residues. The most common are APP695, APP751, and APP770, of which APP695 is highly expressed in the central nervous system. APP is a type I transmembrane glycoprotein with a molecular weight of about 110~130 kDa, with a large extracellular (amino terminal) domain and a small cytoplasmic tail region (intracellular carboxyl terminal). APP is metabolized mainly through two pathways: amyloid (β) pathway and non-amyloid (α) pathway. The amyloid pathway is that APP is cleaved by β-secretase into sAPPβ and a C-terminal fragment containing 99 amino acids. The latter is further cleaved by γ-secreting enzymes into Aβ and ACID, and the Aβ generated by this pathway accounts for 90% to 95% of the total Aβ, including two types of Aβ1-40 and Aβ1-42, of which the content of Aβ1-40 is higher, but Aβ1-42 has A strong hydrophobic effect, its toxicity is greater, and it is easy to polymerization. These Aβ fragments accumulate in mitochondria, lysosomes, and the endoplasmic reticulum, causing these suborganelles to malfunction. In the non-starchy source pathway based on alpha secretase, the alpha secretase cuts APP into sAPP and a C-terminal fragment containing 83 amino acids, which is then cut by gamma secretase to produce P3 and ACID, but these small fragments are cleared by neurons. The mutation of APP gene can cause abnormal protein expression or hydrolysis change, thus affecting the content and composition of Aβ in cells. Aβ mainly exists in the brain in the form of Aβ40 and Aβ42, and the content of Aβ42 is low (< 10%), but easy to aggregate, and then fibrosis and deposition, thus forming a diffuse senile plaque, which is also one of the main pathological characteristics of AD. Moreover, Aβ produced by APP after cleavage by β- and γ-secretory enzymes on the cell membrane can cause oxidative stress, calcium ion inflow, and then damage mitochondria, leading to nerve cell disorders, activation of apoptosis-related proteins and factors, and finally start the apoptosis process of cells. In addition, Aβ can also indirectly cause neuronal apoptosis by causing inflammation in the brain and neurofibrillary tangles, which is an important reason for the formation and development of AD.