Jingsheng Xia

CATSPER Channel-Mediated Ca2+ Entry into Mouse Sperm Triggers a Tail-to-Head Propagation

Abstract Many Ca2+ channel proteins have been detected in mammalian sperm, but only the four CATSPER channels have been clearly shown to be required for male fertility. Ca2+ entry through the principal piece-localized CATSPER channels has been implicated in the activation of hyperactivated motility. In the present study, we show that the Ca2+ entry also triggers a tail-to-head Ca2+ propagation in the mouse sperm. When activated with 8-Br-cAMP, 8-Br-cGMP, or alkaline depolarization, a CATSPER-dependent increase in intracellular Ca2+ concentration starts in the principal piece, propagates through the midpiece, and reaches the head in a few seconds. The Ca2+ propagation through the midpiece leads to a Ca2+-dependent increase in NADH fluorescence. In addition, CatSper1-mutant sperm have lower intracellular ATP levels than wild-type sperm. Thus, a Ca2+ influx in the principal piece through CATSPER channels can not only initiate hyperactivated motility, but can also trigger a tail-to-head Ca2+ propagation that leads to an increase in [NADH] and may regulate ATP homeostasis.

CATSPERβ : A NOVEL TRANSMEMBRANE PROTEIN IN THE CATSPER CHANNEL COMPLEX *

Four CatSper ion channel subunit genes (CatSpers 1-4) are required for sperm cell hyperactivation and male fertility. The four proteins assemble (presumably as a tetramer) to form a sperm-specific, alkalinization-activated Ca2+-selective channel. We set out to identify proteins associating with CatSper that might help explain its unique role in spermatozoa. Using a transgenic approach, a CatSper1 complex was purified from mouse testis that contained heat shock protein 70-2, a testis-specific chaperone, and CatSperβ, a novel protein with two putative transmembrane-spanning domains. Like the CatSper ion channel subunits, CatSperβ was restricted to testis and localized to the principal piece of the sperm tail. CatSperβ protein is absent in CatSper1-/- sperm, suggesting that it is required for trafficking or formation of a stable channel complex. CatSperβ is the first identified auxiliary protein to the CatSper channel.

Neurons respond directly to mechanical deformation with pannexin-mediated ATP release and autostimulation of P2X7 receptors.

•  Neurons can be damaged when tissues are stretched or swollen; while astrocytes can contribute to this process, the mechanosensitive response from neurons is unclear. •  We show here that isolated retinal ganglion cell neurons respond to mechanical strain with a rapid, sustained release of the neurotransmitter ATP. •  The conduit for ATP release was through pannexin hemichannels, with probenicid, carbenoxelone and 10panx inhibiting release. •  Once released, this ATP acts back on the neurons to autostimulate lethal P2X7 receptors, as A438079, AZ 10606120 and zinc reduced currents in whole cell patch clamp recordings. •  Blocking release of ATP through pannexin channels, or activation of P2X7 receptors, might be neuroprotective for stretched or swollen neurons. •  Stretch‐dependent release of ATP through neuronal pannexins, combined with the autostimulation of the P2X7 receptors, provides a new pathway by which neuronal activity and health can be altered by mechanical strain independently of glial activity.

Calcium Signaling Through CatSper Channels in Mammalian Fertilization

The molecular mechanisms underlying Ca(2+) entry into sperm are now much more well defined thanks to direct recordings of mature sperm cells. This article reviews the function of a sperm-specific ion channel, CatSper. CatSpers have a clearly defined function in sperms hyperactivated motility and are essential for male fertility. We propose that physiological stimuli such as zona pellucida and cyclic nucleotides induce Ca(2+) entry through CatSper channels instead of acting on Ca(V) and CNG channels as previously thought.

Mechanosensitive release of adenosine 5′-triphosphate through pannexin channels and mechanosensitive upregulation of pannexin channels in optic nerve head astrocytes: A mechanism for purinergic involvement in chronic strain

As adenosine 5′‐triphosphate (ATP) released from astrocytes can modulate many neural signaling systems, the triggers and pathways for this ATP release are important. Here, the ability of mechanical strain to trigger ATP release through pannexin channels and the effects of sustained strain on pannexin expression were examined in rat optic nerve head astrocytes. Astrocytes released ATP when subjected to 5% of equibiaxial strain or to hypotonic swelling. Although astrocytes expressed mRNA for pannexins 1–3, connexin 43, and VNUT, pharmacological analysis suggested a predominant role for pannexins in mechanosensitive ATP release, with Rho kinase contribution. Astrocytes from panx1−/− mice had reduced baseline and stimulated levels of extracellular ATP, confirming the role for pannexins. Swelling astrocytes triggered a regulatory volume decrease that was inhibited by apyrase or probenecid. The swelling‐induced rise in calcium was inhibited by P2X7 receptor antagonists A438079 and AZ10606120, in addition to apyrase and carbenoxolone. Extended stretch of astrocytes in vitro upregulated expression of panx1 and panx2 mRNA. A similar upregulation was observed in vivo in optic nerve head tissue from the Tg‐MYOCY437H mouse model of chronic glaucoma; genes for panx1, panx2, and panx3 were increased, whereas immunohistochemistry confirmed increased expression of pannexin 1 protein. In summary, astrocytes released ATP in response to mechanical strain, with pannexin 1 the predominant efflux pathway. Sustained strain upregulated pannexins in vitro and in vivo. Together, these findings provide a mechanism by which extracellular ATP remains elevated under chronic mechanical strain, as found in the optic nerve head of patients with glaucoma. GLIA 2014;62:1486–1501

Egg coat proteins activate calcium entry into mouse sperm via CATSPER channels.

Abstract During mammalian fertilization, the contact between sperm and egg triggers increases in intracellular Ca2+ concentration ([Ca2++]i) in sperm. Voltage-gated Ca2+ channels (CaVs) are believed to mediate the initial phase of [Ca2+]i increases in sperm induced by egg coat (zona pellucida [ZP]) glycoproteins, while store depletion-activated Ca2+ entry is thought to mediate the sustained phase. Using patch-clamp recording and Ca2+ imaging, we show herein that CaV channel currents, while found in spermatogenic cells, are not detectable in epididymal sperm and are not essential for the ZP-induced [Ca2+]i changes. Instead, CATSPER channels localized in the distal portion of sperm (the principal piece) are required for the ZP-induced [Ca2+]i increases. Furthermore, the ZP-induced [Ca2+]i increase starts from the sperm tail and propagates toward the head.