Tissue homeostasis

Dihydroxyvitamin (283) is the endogenous ligand for the vitamin receptor (VDR). It modulates genomic function in a tissue and developmentaHy specific manner and affects ceU proliferation, differentiation, and mineral homeostasis (74). Vitamin mobilizes calcium from the bone to maintain plasma Ca " levels. Vitamin and VDR are present in the CNS where they may play a role in regulating Ca " homeostasis. Vitamin D has potent immunomodulatory activity in vivo. 

Glial cells are cells within the central or peripheral nervous system which are not immediately involved in information processing. Glial cells play an mportant role in the metabolic homeostasis of brain tissue and in nervous system development. 

Melanocortins. Figure 3 Melanocortins have the potential to restore homeostasis to tissue. 

Melanocortin peptides are potent anti-inflammatory agents displaying beneficial effects in diseases ranging from cardiovascular to arthritis to obesity to name a few. Within an inflammatory context, they have the ability to switch off early production of cytokines and at later stages they increase levels of anti-inflammatory proteins that lead to the resolution of the host inflammatory response potentially restoring homeostasis to the tissue. They could eventually be viewed as an alternative to glucocorticoids, as their mode of action often resembles that seen... 

As mentioned above, many transcription factors are not always active. Rather the activity of transcription factors is often achieved by induced reversible modification. Most frequently is the addition of phosphate groups (phosphorylation) to Ser, Thr, or Tyr residues. For the AP-1 component c-Jun the phosphorylation at Ser63 and Ser73 enhances activity when cells are subjected to stress, e.g. radiation. Phosphorylation is, however, dispensable for c-Jun-dqDendent tissue homeostasis in the liver, indicating that certain activities do not require the regulatory enhancement. Jun-N-teiminal kinase and a kinase called RSK or p38 catalyze the phosphorylation of AP-1. 

Wallimann, T., Wyss. M., Brdicza, D., Nicolay, K.. Eppenberger, H.M. (1992). Intracellular compartmentation. structure and function of creatine kinase isoenzymes in tissues with high and fluctuating energy demands The phosphocreatine circuit for cellular energy homeostasis. Biochem. J. 281,21-40. 

Because of their strategic localization, astrocytes play a crucial role in maintaining the extracellular ionic homeostasis, provide energetic metabolites to neurons and remove excess of neurotransmitter in schedule with synaptic activity. In addition, the strategic location of astrocytes allows them to carefully monitor and control the level of synaptic activity. Indeed, number of papers during the last 15 years have shown that cultured astrocytes can respond to a variety of neurotransmitters with a variety of different patterns of intracellular calcium increases (Verkhratsky et al. 1998). Later on, studies performed in intact tissue preparations (acute brain slices) further established that the plasma membrane receptors can sense external inputs (such as the spillover of neurotransmitters during intense synaptic activity) and transduce them as intracellular calcium elevations, mostly via release of calcium from internal stores (Dani et al. 1992 Murphy et al. 1993 Porter and McCarthy... 

Cook DN, Prosser DM, Forster R, et al. CCR6 mediates dendritic cell localization, lymphocyte homeostasis, and immune responses in mucosal tissue. Immunity 2000 12(5) 495-503. 

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