Monomeric α-synuclein activates the plasma membrane calcium pump

Alpha-synuclein (aSN) is a membrane-associated and intrinsically disordered protein, well known for pathological aggregation in neurodegeneration. However, the physiological function of aSN is disputed. Pull-down experiments have pointed to plasma membrane Ca2+ -ATPase (PMCA) as a potential interaction partner. From proximity ligation assays, we find that aSN and PMCA colocalize at neuronal synapses, and we show that calcium expulsion is activated by aSN and PMCA. We further show that soluble, monomeric aSN activates PMCA at par with calmodulin, but independent of the autoinhibitory domain of PMCA, and highly dependent on acidic phospholipids and membrane-anchoring properties of aSN. On PMCA, the key site is mapped to the acidic lipid-binding site, located within a disordered PMCA-specific loop connecting the cytosolic A domain and transmembrane segment 3. Our studies point toward a novel physiological role of monomeric aSN as a stimulator of calcium clearance in neurons through activation of PMCA.

JNK signaling pathway regulates sorbitol-induced Tau proteolysis and apoptosis in SH-SY5Y cells by targeting caspase-3

Growing evidence suggests that Diabetes Mellitus increases the risk of developing Alzheimer's disease. It is well known that hyperglycemia, a key feature of Diabetes Mellitus, may induce plasma osmolarity disturbances. Both hyperglycemia and hyperosmolarity promote the altered post-translational regulation of microtubule-associated protein Tau. Interestingly, abnormal hyperphosphorylation and cleavage of Tau have been proven to lead to the genesis of filamentous structures referred to as neurofibrillary tangles, the main pathological hallmark of Alzheimer's disease. We have previously described that hyperosmotic stress induced by sorbitol promotes Tau proteolysis and apoptosis in SH-SY5Y cells via caspase-3 activation. In order to gain insights into the regulatory mechanisms of such processes, in this work we explored the intracellular signaling pathways that regulate these events. We found that sorbitol treatment significantly enhanced the activation of conventional families of MAPK in SH-SY5Y cells. Tau proteolysis was completely prevented by JNK inhibition but not affected by either ERK1/2 or p38 MAPK blockade. Moreover, inhibition of JNK, but not ERK1/2 or p38 MAPK, efficiently prevented sorbitol-induced apoptosis and caspase-3 activation. In summary, we provide evidence that JNK signaling pathway is an upstream regulator of hyperosmotic stress-induced Tau cleavage and apoptosis in SH-SY5Y through the control of caspase-3 activation.

[Incidence and clinical features of splenic abscesses, with special reference to tuberculous etiology in a general hospital]

BACKGROUND

The aim of this revision is to know the incidence of splenic abscess (SA) in our hospital, its etiology, with special reference to tuberculosis, and clinical characteristics.

PATIENTS AND METHODS

Abdominal CT-scan performed during the period 1987-1997, with the diagnosis of splenic abscess were reviewed. Etiologic diagnosis standed on blood or sputum cultures, PAAF and/or histologic study of lymph nodes.

RESULTS

Seventeen cases of SA were obtained, 12 males and 5 females. Limits of age: 13 and 77 years. The causal microorganisms were: M. tuberculosis (7), Mycobacterium aviumintracellulare (1), S. aureus (2), S. anginosus (1), S. milleri (1), E. coli (1), C. albicans (1), T. biguelle (1) and polymicrobian flora (1). One case was of unknown etiology. Underlying illnesses were: AIDS (7), malignant neoplasms (3), diabetes (2), endocarditis (2), Sjögren syndrome (1) and complications of abdominal surgery (2). Clinical presentation in nontuberculous splenic abscess was fever and upper-left abdominal pain. Predominant symptoms in tuberculous splenic abscess were fever and weight loss. Blood cultures were positive in 80% of non tuberculous splenic abscess. Specific treatment for tuberculosis improved all patients with tuberculous splenic abscess, without needing surgery or corticosteroids.

CONCLUSIONS

From the total of splenic abscess, 41.1% were tuberculous, six with AIDS and one with Sjögren syndrome. Diabetes and malignant neoplasms were the commonest underlying illnesses in the non-tuberculous. In these, clinical presentation consisted in fever and upper-left abdominal pain. In patients with tuberculous splenic abscess, the main complaint was weight loss. A prompt treatment is generally succesful.